Finish rework of bt_deletekey, w/bug fixes

[btree] / threads2h.c

// btree version threads2h pthread rw lock version
//      with reworked bt_deletekey code
// 12 FEB 2014

// author: karl malbrain, malbrain@cal.berkeley.edu

/*
This work, including the source code, documentation
and related data, is placed into the public domain.

The orginal author is Karl Malbrain.

THIS SOFTWARE IS PROVIDED AS-IS WITHOUT WARRANTY
OF ANY KIND, NOT EVEN THE IMPLIED WARRANTY OF
MERCHANTABILITY. THE AUTHOR OF THIS SOFTWARE,
ASSUMES _NO_ RESPONSIBILITY FOR ANY CONSEQUENCE
RESULTING FROM THE USE, MODIFICATION, OR
REDISTRIBUTION OF THIS SOFTWARE.
*/

// Please see the project home page for documentation
// code.google.com/p/high-concurrency-btree

#define _FILE_OFFSET_BITS 64
#define _LARGEFILE64_SOURCE

#ifdef linux
#define _GNU_SOURCE
#endif

#ifdef unix
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <errno.h>
#include <pthread.h>
#else
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <fcntl.h>
#include <process.h>
#include <intrin.h>
#endif

#include <memory.h>
#include <string.h>
#include <stddef.h>

typedef unsigned long long      uid;

#ifndef unix
typedef unsigned long long      off64_t;
typedef unsigned short          ushort;
typedef unsigned int            uint;
#endif

#define BT_latchtable   128                                     // number of latch manager slots

#define BT_ro 0x6f72    // ro
#define BT_rw 0x7772    // rw

#define BT_maxbits              24                                      // maximum page size in bits
#define BT_minbits              9                                       // minimum page size in bits
#define BT_minpage              (1 << BT_minbits)       // minimum page size
#define BT_maxpage              (1 << BT_maxbits)       // maximum page size

/*
There are five lock types for each node in three independent sets: 
1. (set 1) AccessIntent: Sharable. Going to Read the node. Incompatible with NodeDelete. 
2. (set 1) NodeDelete: Exclusive. About to release the node. Incompatible with AccessIntent. 
3. (set 2) ReadLock: Sharable. Read the node. Incompatible with WriteLock. 
4. (set 2) WriteLock: Exclusive. Modify the node. Incompatible with ReadLock and other WriteLocks. 
5. (set 3) ParentModification: Exclusive. Change the node's parent keys. Incompatible with another ParentModification. 
*/

typedef enum{
        BtLockAccess,
        BtLockDelete,
        BtLockRead,
        BtLockWrite,
        BtLockParent
} BtLock;

//      mode & definition for latch implementation

enum {
        Mutex = 1,
        Write = 2,
        Pending = 4,
        Share = 8
} LockMode;

// exclusive is set for write access
// share is count of read accessors
// grant write lock when share == 0

typedef struct {
        volatile ushort mutex:1;
        volatile ushort exclusive:1;
        volatile ushort pending:1;
        volatile ushort share:13;
} BtSpinLatch;

//  hash table entries

typedef struct {
        BtSpinLatch latch[1];
        volatile ushort slot;           // Latch table entry at head of chain
} BtHashEntry;

//      latch manager table structure

typedef struct {
#ifdef unix
        pthread_rwlock_t lock[1];
#else
        SRWLOCK srw[1];
#endif
} BtLatch;

typedef struct {
        BtLatch readwr[1];                      // read/write page lock
        BtLatch access[1];                      // Access Intent/Page delete
        BtLatch parent[1];                      // Posting of fence key in parent
        BtSpinLatch busy[1];            // slot is being moved between chains
        volatile ushort next;           // next entry in hash table chain
        volatile ushort prev;           // prev entry in hash table chain
        volatile ushort pin;            // number of outstanding locks
        volatile ushort hash;           // hash slot entry is under
        volatile uid page_no;           // latch set page number
} BtLatchSet;

//      Define the length of the page and key pointers

#define BtId 6

//      Page key slot definition.

//      If BT_maxbits is 15 or less, you can save 4 bytes
//      for each key stored by making the first two uints
//      into ushorts.  You can also save 4 bytes by removing
//      the tod field from the key.

//      Keys are marked dead, but remain on the page until
//      it cleanup is called. The fence key (highest key) for
//      the page is always present, even after cleanup.

typedef struct {
        uint off:BT_maxbits;            // page offset for key start
        uint dead:1;                            // set for deleted key
        uint tod;                                       // time-stamp for key
        unsigned char id[BtId];         // id associated with key
} BtSlot;

//      The key structure occupies space at the upper end of
//      each page.  It's a length byte followed by the value
//      bytes.

typedef struct {
        unsigned char len;
        unsigned char key[1];
} *BtKey;

//      The first part of an index page.
//      It is immediately followed
//      by the BtSlot array of keys.

typedef struct BtPage_ {
        uint cnt;                                       // count of keys in page
        uint act;                                       // count of active keys
        uint min;                                       // next key offset
        unsigned char bits:7;           // page size in bits
        unsigned char free:1;           // page is on free list
        unsigned char lvl:4;            // level of page
        unsigned char kill:1;           // page is being killed
        unsigned char dirty:1;          // page has deleted keys
        unsigned char posted:1;         // page fence is posted
        unsigned char goright:1;        // page is being killed, continue to right
        unsigned char right[BtId];      // page number to right
        unsigned char fence[256];       // page fence key
} *BtPage;

//      The memory mapping pool table buffer manager entry

typedef struct {
        unsigned long long int lru;     // number of times accessed
        uid  basepage;                          // mapped base page number
        char *map;                                      // mapped memory pointer
        ushort slot;                            // slot index in this array
        ushort pin;                                     // mapped page pin counter
        void *hashprev;                         // previous pool entry for the same hash idx
        void *hashnext;                         // next pool entry for the same hash idx
#ifndef unix
        HANDLE hmap;                            // Windows memory mapping handle
#endif
} BtPool;

//  The loadpage interface object

typedef struct {
        uid page_no;            // current page number
        BtPage page;            // current page pointer
        BtPool *pool;           // current page pool
        BtLatchSet *latch;      // current page latch set
} BtPageSet;

//      structure for latch manager on ALLOC_page

typedef struct {
        struct BtPage_ alloc[2];        // next & free page_nos in right ptr
        BtSpinLatch lock[1];            // allocation area lite latch
        ushort latchdeployed;           // highest number of latch entries deployed
        ushort nlatchpage;                      // number of latch pages at BT_latch
        ushort latchtotal;                      // number of page latch entries
        ushort latchhash;                       // number of latch hash table slots
        ushort latchvictim;                     // next latch entry to examine
        BtHashEntry table[0];           // the hash table
} BtLatchMgr;

//      The object structure for Btree access

typedef struct {
        uint page_size;                         // page size    
        uint page_bits;                         // page size in bits    
        uint seg_bits;                          // seg size in pages in bits
        uint mode;                                      // read-write mode
#ifdef unix
        int idx;
#else
        HANDLE idx;
#endif
        ushort poolcnt;                         // highest page pool node in use
        ushort poolmax;                         // highest page pool node allocated
        ushort poolmask;                        // total number of pages in mmap segment - 1
        ushort hashsize;                        // size of Hash Table for pool entries
        volatile uint evicted;          // last evicted hash table slot
        ushort *hash;                           // pool index for hash entries
        BtSpinLatch *latch;                     // latches for hash table slots
        BtLatchMgr *latchmgr;           // mapped latch page from allocation page
        BtLatchSet *latchsets;          // mapped latch set from latch pages
        BtPool *pool;                           // memory pool page segments
#ifndef unix
        HANDLE halloc;                          // allocation and latch table handle
#endif
} BtMgr;

typedef struct {
        BtMgr *mgr;                     // buffer manager for thread
        BtPage cursor;          // cached frame for start/next (never mapped)
        BtPage frame;           // spare frame for the page split (never mapped)
        BtPage zero;            // page frame for zeroes at end of file
        uid cursor_page;        // current cursor page number   
        unsigned char *mem;     // frame, cursor, page memory buffer
        int found;                      // last delete or insert was found
        int err;                        // last error
} BtDb;

typedef enum {
        BTERR_ok = 0,
        BTERR_struct,
        BTERR_ovflw,
        BTERR_lock,
        BTERR_map,
        BTERR_wrt,
        BTERR_hash
} BTERR;

// B-Tree functions
extern void bt_close (BtDb *bt);
extern BtDb *bt_open (BtMgr *mgr);
extern BTERR bt_insertkey (BtDb *bt, unsigned char *key, uint len, uid id, uint tod, uint lvl);
extern BTERR  bt_deletekey (BtDb *bt, unsigned char *key, uint len);
extern uid bt_findkey    (BtDb *bt, unsigned char *key, uint len);
extern uint bt_startkey  (BtDb *bt, unsigned char *key, uint len);
extern uint bt_nextkey   (BtDb *bt, uint slot);

//      internal functions
BTERR bt_removepage (BtDb *bt, BtPageSet *set, uint lvl, unsigned char *pagefence);

//      manager functions
extern BtMgr *bt_mgr (char *name, uint mode, uint bits, uint poolsize, uint segsize, uint hashsize);
void bt_mgrclose (BtMgr *mgr);

//  Helper functions to return slot values

extern BtKey bt_key (BtDb *bt, uint slot);
extern uid bt_uid (BtDb *bt, uint slot);
extern uint bt_tod (BtDb *bt, uint slot);

//  BTree page number constants
#define ALLOC_page              0       // allocation & lock manager hash table
#define ROOT_page               1       // root of the btree
#define LEAF_page               2       // first page of leaves
#define LATCH_page              3       // pages for lock manager

//      Number of levels to create in a new BTree

#define MIN_lvl                 2

//  The page is allocated from low and hi ends.
//  The key offsets and row-id's are allocated
//  from the bottom, while the text of the key
//  is allocated from the top.  When the two
//  areas meet, the page is split into two.

//  A key consists of a length byte, two bytes of
//  index number (0 - 65534), and up to 253 bytes
//  of key value.  Duplicate keys are discarded.
//  Associated with each key is a 48 bit row-id.

//  The b-tree root is always located at page 1.
//      The first leaf page of level zero is always
//      located on page 2.

//      The b-tree pages are linked with next
//      pointers to facilitate enumerators,
//      and provide for concurrency.

//      When to root page fills, it is split in two and
//      the tree height is raised by a new root at page
//      one with two keys.

//      Deleted keys are marked with a dead bit until
//      page cleanup The fence key for a node is
//      present in a special array.

//  Groups of pages called segments from the btree are optionally
//  cached with a memory mapped pool. A hash table is used to keep
//  track of the cached segments.  This behaviour is controlled
//  by the cache block size parameter to bt_open.

//  To achieve maximum concurrency one page is locked at a time
//  as the tree is traversed to find leaf key in question. The right
//  page numbers are used in cases where the page is being split,
//      or consolidated.

//  Page 0 is dedicated to lock for new page extensions,
//      and chains empty pages together for reuse.

//      The ParentModification lock on a node is obtained to serialize posting
//      or changing the fence key for a node.

//      Empty pages are chained together through the ALLOC page and reused.

//      Access macros to address slot and key values from the page.
//      Page slots use 1 based indexing.

#define slotptr(page, slot) (((BtSlot *)(page+1)) + (slot-1))
#define keyptr(page, slot) ((BtKey)((unsigned char*)(page) + slotptr(page, slot)->off))

void bt_putid(unsigned char *dest, uid id)
{
int i = BtId;

        while( i-- )
                dest[i] = (unsigned char)id, id >>= 8;
}

uid bt_getid(unsigned char *src)
{
uid id = 0;
int i;

        for( i = 0; i < BtId; i++ )
                id <<= 8, id |= *src++; 

        return id;
}

//      Latch Manager

//      wait until write lock mode is clear
//      and add 1 to the share count

void bt_spinreadlock(BtSpinLatch *latch)
{
ushort prev;

  do {
        //      obtain latch mutex
#ifdef unix
        if( __sync_fetch_and_or((ushort *)latch, Mutex) & Mutex )
                continue;
#else
        if( prev = _InterlockedOr16((ushort *)latch, Mutex) & Mutex )
                continue;
#endif
        //  see if exclusive request is granted or pending

        if( prev = !(latch->exclusive | latch->pending) )
#ifdef unix
                __sync_fetch_and_add((ushort *)latch, Share);
#else
                _InterlockedExchangeAdd16 ((ushort *)latch, Share);
#endif

#ifdef unix
        __sync_fetch_and_and ((ushort *)latch, ~Mutex);
#else
        _InterlockedAnd16((ushort *)latch, ~Mutex);
#endif

        if( prev )
                return;
#ifdef  unix
  } while( sched_yield(), 1 );
#else
  } while( SwitchToThread(), 1 );
#endif
}

//      wait for other read and write latches to relinquish

void bt_spinwritelock(BtSpinLatch *latch)
{
  do {
#ifdef  unix
        if( __sync_fetch_and_or((ushort *)latch, Mutex | Pending) & Mutex )
                continue;
#else
        if( _InterlockedOr16((ushort *)latch, Mutex | Pending) & Mutex )
                continue;
#endif
        if( !(latch->share | latch->exclusive) ) {
#ifdef unix
                __sync_fetch_and_or((ushort *)latch, Write);
                __sync_fetch_and_and ((ushort *)latch, ~(Mutex | Pending));
#else
                _InterlockedOr16((ushort *)latch, Write);
                _InterlockedAnd16((ushort *)latch, ~(Mutex | Pending));
#endif
                return;
        }

#ifdef unix
        __sync_fetch_and_and ((ushort *)latch, ~Mutex);
#else
        _InterlockedAnd16((ushort *)latch, ~Mutex);
#endif

#ifdef  unix
  } while( sched_yield(), 1 );
#else
  } while( SwitchToThread(), 1 );
#endif
}

//      try to obtain write lock

//      return 1 if obtained,
//              0 otherwise

int bt_spinwritetry(BtSpinLatch *latch)
{
ushort prev;

#ifdef unix
        if( prev = __sync_fetch_and_or((ushort *)latch, Mutex), prev & Mutex )
                return 0;
#else
        if( prev = _InterlockedOr16((ushort *)latch, Mutex), prev & Mutex )
                return 0;
#endif
        //      take write access if all bits are clear

        if( !prev )
#ifdef unix
                __sync_fetch_and_or ((ushort *)latch, Write);
#else
                _InterlockedOr16((ushort *)latch, Write);
#endif

#ifdef unix
        __sync_fetch_and_and ((ushort *)latch, ~Mutex);
#else
        _InterlockedAnd16((ushort *)latch, ~Mutex);
#endif
        return !prev;
}

//      clear write mode

void bt_spinreleasewrite(BtSpinLatch *latch)
{
#ifdef unix
        __sync_fetch_and_and ((ushort *)latch, ~Write);
#else
        _InterlockedAnd16((ushort *)latch, ~Write);
#endif
}

//      decrement reader count

void bt_spinreleaseread(BtSpinLatch *latch)
{
#ifdef unix
        __sync_fetch_and_add((ushort *)latch, -Share);
#else
        _InterlockedExchangeAdd16 ((ushort *)latch, -Share);
#endif
}

void bt_readlock(BtLatch *latch)
{
#ifdef unix
        pthread_rwlock_rdlock (latch->lock);
#else
        AcquireSRWLockShared (latch->srw);
#endif
}

//      wait for other read and write latches to relinquish

void bt_writelock(BtLatch *latch)
{
#ifdef unix
        pthread_rwlock_wrlock (latch->lock);
#else
        AcquireSRWLockExclusive (latch->srw);
#endif
}

//      try to obtain write lock

//      return 1 if obtained,
//              0 if already write or read locked

int bt_writetry(BtLatch *latch)
{
int result = 0;

#ifdef unix
        result = !pthread_rwlock_trywrlock (latch->lock);
#else
        result = TryAcquireSRWLockExclusive (latch->srw);
#endif
        return result;
}

//      clear write mode

void bt_releasewrite(BtLatch *latch)
{
#ifdef unix
        pthread_rwlock_unlock (latch->lock);
#else
        ReleaseSRWLockExclusive (latch->srw);
#endif
}

//      decrement reader count

void bt_releaseread(BtLatch *latch)
{
#ifdef unix
        pthread_rwlock_unlock (latch->lock);
#else
        ReleaseSRWLockShared (latch->srw);
#endif
}

void bt_initlockset (BtLatchSet *set)
{
#ifdef unix
pthread_rwlockattr_t rwattr[1];

        pthread_rwlockattr_init (rwattr);
        pthread_rwlockattr_setpshared (rwattr, PTHREAD_PROCESS_SHARED);

        pthread_rwlock_init (set->readwr->lock, rwattr);
        pthread_rwlock_init (set->access->lock, rwattr);
        pthread_rwlock_init (set->parent->lock, rwattr);
        pthread_rwlockattr_destroy (rwattr);
#else
        InitializeSRWLock (set->readwr->srw);
        InitializeSRWLock (set->access->srw);
        InitializeSRWLock (set->parent->srw);
#endif
}

//      link latch table entry into latch hash table

void bt_latchlink (BtDb *bt, ushort hashidx, ushort victim, uid page_no)
{
BtLatchSet *set = bt->mgr->latchsets + victim;

        if( set->next = bt->mgr->latchmgr->table[hashidx].slot )
                bt->mgr->latchsets[set->next].prev = victim;

        bt->mgr->latchmgr->table[hashidx].slot = victim;
        set->page_no = page_no;
        set->hash = hashidx;
        set->prev = 0;
}

//      release latch pin

void bt_unpinlatch (BtLatchSet *set)
{
#ifdef unix
        __sync_fetch_and_add(&set->pin, -1);
#else
        _InterlockedDecrement16 (&set->pin);
#endif
}

//      find existing latchset or inspire new one
//      return with latchset pinned

BtLatchSet *bt_pinlatch (BtDb *bt, uid page_no)
{
ushort hashidx = page_no % bt->mgr->latchmgr->latchhash;
ushort slot, avail = 0, victim, idx;
BtLatchSet *set;

        //  obtain read lock on hash table entry

        bt_spinreadlock(bt->mgr->latchmgr->table[hashidx].latch);

        if( slot = bt->mgr->latchmgr->table[hashidx].slot ) do
        {
                set = bt->mgr->latchsets + slot;
                if( page_no == set->page_no )
                        break;
        } while( slot = set->next );

        if( slot ) {
#ifdef unix
                __sync_fetch_and_add(&set->pin, 1);
#else
                _InterlockedIncrement16 (&set->pin);
#endif
        }

    bt_spinreleaseread (bt->mgr->latchmgr->table[hashidx].latch);

        if( slot )
                return set;

  //  try again, this time with write lock

  bt_spinwritelock(bt->mgr->latchmgr->table[hashidx].latch);

  if( slot = bt->mgr->latchmgr->table[hashidx].slot ) do
  {
        set = bt->mgr->latchsets + slot;
        if( page_no == set->page_no )
                break;
        if( !set->pin && !avail )
                avail = slot;
  } while( slot = set->next );

  //  found our entry, or take over an unpinned one

  if( slot || (slot = avail) ) {
        set = bt->mgr->latchsets + slot;
#ifdef unix
        __sync_fetch_and_add(&set->pin, 1);
#else
        _InterlockedIncrement16 (&set->pin);
#endif
        set->page_no = page_no;
        bt_spinreleasewrite(bt->mgr->latchmgr->table[hashidx].latch);
        return set;
  }

        //  see if there are any unused entries
#ifdef unix
        victim = __sync_fetch_and_add (&bt->mgr->latchmgr->latchdeployed, 1) + 1;
#else
        victim = _InterlockedIncrement16 (&bt->mgr->latchmgr->latchdeployed);
#endif

        if( victim < bt->mgr->latchmgr->latchtotal ) {
                set = bt->mgr->latchsets + victim;
#ifdef unix
                __sync_fetch_and_add(&set->pin, 1);
#else
                _InterlockedIncrement16 (&set->pin);
#endif
                bt_initlockset (set);
                bt_latchlink (bt, hashidx, victim, page_no);
                bt_spinreleasewrite (bt->mgr->latchmgr->table[hashidx].latch);
                return set;
        }

#ifdef unix
        victim = __sync_fetch_and_add (&bt->mgr->latchmgr->latchdeployed, -1);
#else
        victim = _InterlockedDecrement16 (&bt->mgr->latchmgr->latchdeployed);
#endif
  //  find and reuse previous lock entry

  while( 1 ) {
#ifdef unix
        victim = __sync_fetch_and_add(&bt->mgr->latchmgr->latchvictim, 1);
#else
        victim = _InterlockedIncrement16 (&bt->mgr->latchmgr->latchvictim) - 1;
#endif
        //      we don't use slot zero

        if( victim %= bt->mgr->latchmgr->latchtotal )
                set = bt->mgr->latchsets + victim;
        else
                continue;

        //      take control of our slot
        //      from other threads

        if( set->pin || !bt_spinwritetry (set->busy) )
                continue;

        idx = set->hash;

        // try to get write lock on hash chain
        //      skip entry if not obtained
        //      or has outstanding locks

        if( !bt_spinwritetry (bt->mgr->latchmgr->table[idx].latch) ) {
                bt_spinreleasewrite (set->busy);
                continue;
        }

        if( set->pin ) {
                bt_spinreleasewrite (set->busy);
                bt_spinreleasewrite (bt->mgr->latchmgr->table[idx].latch);
                continue;
        }

        //  unlink our available victim from its hash chain

        if( set->prev )
                bt->mgr->latchsets[set->prev].next = set->next;
        else
                bt->mgr->latchmgr->table[idx].slot = set->next;

        if( set->next )
                bt->mgr->latchsets[set->next].prev = set->prev;

        bt_spinreleasewrite (bt->mgr->latchmgr->table[idx].latch);
#ifdef unix
        __sync_fetch_and_add(&set->pin, 1);
#else
        _InterlockedIncrement16 (&set->pin);
#endif
        bt_latchlink (bt, hashidx, victim, page_no);
        bt_spinreleasewrite (bt->mgr->latchmgr->table[hashidx].latch);
        bt_spinreleasewrite (set->busy);
        return set;
  }
}

void bt_mgrclose (BtMgr *mgr)
{
BtPool *pool;
uint slot;

        // release mapped pages
        //      note that slot zero is never used

        for( slot = 1; slot < mgr->poolmax; slot++ ) {
                pool = mgr->pool + slot;
                if( pool->slot )
#ifdef unix
                        munmap (pool->map, (mgr->poolmask+1) << mgr->page_bits);
#else
                {
                        FlushViewOfFile(pool->map, 0);
                        UnmapViewOfFile(pool->map);
                        CloseHandle(pool->hmap);
                }
#endif
        }

#ifdef unix
        munmap (mgr->latchsets, mgr->latchmgr->nlatchpage * mgr->page_size);
        munmap (mgr->latchmgr, mgr->page_size);
#else
        FlushViewOfFile(mgr->latchmgr, 0);
        UnmapViewOfFile(mgr->latchmgr);
        CloseHandle(mgr->halloc);
#endif
#ifdef unix
        close (mgr->idx);
        free (mgr->pool);
        free (mgr->hash);
        free (mgr->latch);
        free (mgr);
#else
        FlushFileBuffers(mgr->idx);
        CloseHandle(mgr->idx);
        GlobalFree (mgr->pool);
        GlobalFree (mgr->hash);
        GlobalFree (mgr->latch);
        GlobalFree (mgr);
#endif
}

//      close and release memory

void bt_close (BtDb *bt)
{
#ifdef unix
        if ( bt->mem )
                free (bt->mem);
#else
        if ( bt->mem)
                VirtualFree (bt->mem, 0, MEM_RELEASE);
#endif
        free (bt);
}

//  open/create new btree buffer manager

//      call with file_name, BT_openmode, bits in page size (e.g. 16),
//              size of mapped page pool (e.g. 8192)

BtMgr *bt_mgr (char *name, uint mode, uint bits, uint poolmax, uint segsize, uint hashsize)
{
uint lvl, attr, cacheblk, last, slot, idx;
uint nlatchpage, latchhash;
BtLatchMgr *latchmgr;
off64_t size;
uint amt[1];
BtMgr* mgr;
int flag;

#ifndef unix
SYSTEM_INFO sysinfo[1];
#endif

        // determine sanity of page size and buffer pool

        if( bits > BT_maxbits )
                bits = BT_maxbits;
        else if( bits < BT_minbits )
                bits = BT_minbits;

        if( !poolmax )
                return NULL;    // must have buffer pool

#ifdef unix
        mgr = calloc (1, sizeof(BtMgr));

        mgr->idx = open ((char*)name, O_RDWR | O_CREAT, 0666);

        if( mgr->idx == -1 )
                return free(mgr), NULL;
        
        cacheblk = 4096;        // minimum mmap segment size for unix

#else
        mgr = GlobalAlloc (GMEM_FIXED|GMEM_ZEROINIT, sizeof(BtMgr));
        attr = FILE_ATTRIBUTE_NORMAL;
        mgr->idx = CreateFile(name, GENERIC_READ| GENERIC_WRITE, FILE_SHARE_READ|FILE_SHARE_WRITE, NULL, OPEN_ALWAYS, attr, NULL);

        if( mgr->idx == INVALID_HANDLE_VALUE )
                return GlobalFree(mgr), NULL;

        // normalize cacheblk to multiple of sysinfo->dwAllocationGranularity
        GetSystemInfo(sysinfo);
        cacheblk = sysinfo->dwAllocationGranularity;
#endif

#ifdef unix
        latchmgr = malloc (BT_maxpage);
        *amt = 0;

        // read minimum page size to get root info

        if( size = lseek (mgr->idx, 0L, 2) ) {
                if( pread(mgr->idx, latchmgr, BT_minpage, 0) == BT_minpage )
                        bits = latchmgr->alloc->bits;
                else
                        return free(mgr), free(latchmgr), NULL;
        } else if( mode == BT_ro )
                return free(latchmgr), bt_mgrclose (mgr), NULL;
#else
        latchmgr = VirtualAlloc(NULL, BT_maxpage, MEM_COMMIT, PAGE_READWRITE);
        size = GetFileSize(mgr->idx, amt);

        if( size || *amt ) {
                if( !ReadFile(mgr->idx, (char *)latchmgr, BT_minpage, amt, NULL) )
                        return bt_mgrclose (mgr), NULL;
                bits = latchmgr->alloc->bits;
        } else if( mode == BT_ro )
                return bt_mgrclose (mgr), NULL;
#endif

        mgr->page_size = 1 << bits;
        mgr->page_bits = bits;

        mgr->poolmax = poolmax;
        mgr->mode = mode;

        if( cacheblk < mgr->page_size )
                cacheblk = mgr->page_size;

        //  mask for partial memmaps

        mgr->poolmask = (cacheblk >> bits) - 1;

        //      see if requested size of pages per memmap is greater

        if( (1 << segsize) > mgr->poolmask )
                mgr->poolmask = (1 << segsize) - 1;

        mgr->seg_bits = 0;

        while( (1 << mgr->seg_bits) <= mgr->poolmask )
                mgr->seg_bits++;

        mgr->hashsize = hashsize;

#ifdef unix
        mgr->pool = calloc (poolmax, sizeof(BtPool));
        mgr->hash = calloc (hashsize, sizeof(ushort));
        mgr->latch = calloc (hashsize, sizeof(BtSpinLatch));
#else
        mgr->pool = GlobalAlloc (GMEM_FIXED|GMEM_ZEROINIT, poolmax * sizeof(BtPool));
        mgr->hash = GlobalAlloc (GMEM_FIXED|GMEM_ZEROINIT, hashsize * sizeof(ushort));
        mgr->latch = GlobalAlloc (GMEM_FIXED|GMEM_ZEROINIT, hashsize * sizeof(BtSpinLatch));
#endif

        if( size || *amt )
                goto mgrlatch;

        // initialize an empty b-tree with latch page, root page, page of leaves
        // and page(s) of latches

        memset (latchmgr, 0, 1 << bits);
        nlatchpage = BT_latchtable / (mgr->page_size / sizeof(BtLatchSet)) + 1; 
        bt_putid(latchmgr->alloc->right, MIN_lvl+1+nlatchpage);
        latchmgr->alloc->bits = mgr->page_bits;

        latchmgr->nlatchpage = nlatchpage;
        latchmgr->latchtotal = nlatchpage * (mgr->page_size / sizeof(BtLatchSet));

        //  initialize latch manager

        latchhash = (mgr->page_size - sizeof(BtLatchMgr)) / sizeof(BtHashEntry);

        //      size of hash table = total number of latchsets

        if( latchhash > latchmgr->latchtotal )
                latchhash = latchmgr->latchtotal;

        latchmgr->latchhash = latchhash;

#ifdef unix
        if( write (mgr->idx, latchmgr, mgr->page_size) < mgr->page_size )
                return bt_mgrclose (mgr), NULL;
#else
        if( !WriteFile (mgr->idx, (char *)latchmgr, mgr->page_size, amt, NULL) )
                return bt_mgrclose (mgr), NULL;

        if( *amt < mgr->page_size )
                return bt_mgrclose (mgr), NULL;
#endif

        memset (latchmgr, 0, 1 << bits);
        latchmgr->alloc->bits = mgr->page_bits;

        for( lvl=MIN_lvl; lvl--; ) {
                slotptr(latchmgr->alloc, 1)->off = offsetof(struct BtPage_, fence);
                bt_putid(slotptr(latchmgr->alloc, 1)->id, lvl ? MIN_lvl - lvl + 1 : 0);         // next(lower) page number
                latchmgr->alloc->fence[0] = 2;
                latchmgr->alloc->fence[1] = 0xff;
                latchmgr->alloc->fence[2] = 0xff;
                latchmgr->alloc->min = mgr->page_size;
                latchmgr->alloc->lvl = lvl;
                latchmgr->alloc->cnt = 1;
                latchmgr->alloc->act = 1;
#ifdef unix
                if( write (mgr->idx, latchmgr, mgr->page_size) < mgr->page_size )
                        return bt_mgrclose (mgr), NULL;
#else
                if( !WriteFile (mgr->idx, (char *)latchmgr, mgr->page_size, amt, NULL) )
                        return bt_mgrclose (mgr), NULL;

                if( *amt < mgr->page_size )
                        return bt_mgrclose (mgr), NULL;
#endif
        }

        // clear out latch manager locks
        //      and rest of pages to round out segment

        memset(latchmgr, 0, mgr->page_size);
        last = MIN_lvl + 1;

        while( last <= ((MIN_lvl + 1 + nlatchpage) | mgr->poolmask) ) {
#ifdef unix
                pwrite(mgr->idx, latchmgr, mgr->page_size, last << mgr->page_bits);
#else
                SetFilePointer (mgr->idx, last << mgr->page_bits, NULL, FILE_BEGIN);
                if( !WriteFile (mgr->idx, (char *)latchmgr, mgr->page_size, amt, NULL) )
                        return bt_mgrclose (mgr), NULL;
                if( *amt < mgr->page_size )
                        return bt_mgrclose (mgr), NULL;
#endif
                last++;
        }

mgrlatch:
#ifdef unix
        flag = PROT_READ | PROT_WRITE;
        mgr->latchmgr = mmap (0, mgr->page_size, flag, MAP_SHARED, mgr->idx, ALLOC_page * mgr->page_size);
        if( mgr->latchmgr == MAP_FAILED )
                return bt_mgrclose (mgr), NULL;
        mgr->latchsets = (BtLatchSet *)mmap (0, mgr->latchmgr->nlatchpage * mgr->page_size, flag, MAP_SHARED, mgr->idx, LATCH_page * mgr->page_size);
        if( mgr->latchsets == MAP_FAILED )
                return bt_mgrclose (mgr), NULL;
#else
        flag = PAGE_READWRITE;
        mgr->halloc = CreateFileMapping(mgr->idx, NULL, flag, 0, (BT_latchtable / (mgr->page_size / sizeof(BtLatchSet)) + 1 + LATCH_page) * mgr->page_size, NULL);
        if( !mgr->halloc )
                return bt_mgrclose (mgr), NULL;

        flag = FILE_MAP_WRITE;
        mgr->latchmgr = MapViewOfFile(mgr->halloc, flag, 0, 0, (BT_latchtable / (mgr->page_size / sizeof(BtLatchSet)) + 1 + LATCH_page) * mgr->page_size);
        if( !mgr->latchmgr )
                return GetLastError(), bt_mgrclose (mgr), NULL;

        mgr->latchsets = (void *)((char *)mgr->latchmgr + LATCH_page * mgr->page_size);
#endif

#ifdef unix
        free (latchmgr);
#else
        VirtualFree (latchmgr, 0, MEM_RELEASE);
#endif
        return mgr;
}

//      open BTree access method
//      based on buffer manager

BtDb *bt_open (BtMgr *mgr)
{
BtDb *bt = malloc (sizeof(*bt));

        memset (bt, 0, sizeof(*bt));
        bt->mgr = mgr;
#ifdef unix
        bt->mem = malloc (3 *mgr->page_size);
#else
        bt->mem = VirtualAlloc(NULL, 3 * mgr->page_size, MEM_COMMIT, PAGE_READWRITE);
#endif
        bt->frame = (BtPage)bt->mem;
        bt->zero = (BtPage)(bt->mem + 1 * mgr->page_size);
        bt->cursor = (BtPage)(bt->mem + 2 * mgr->page_size);

        memset (bt->zero, 0, mgr->page_size);
        return bt;
}

//  compare two keys, returning > 0, = 0, or < 0
//  as the comparison value

int keycmp (BtKey key1, unsigned char *key2, uint len2)
{
uint len1 = key1->len;
int ans;

        if( ans = memcmp (key1->key, key2, len1 > len2 ? len2 : len1) )
                return ans;

        if( len1 > len2 )
                return 1;
        if( len1 < len2 )
                return -1;

        return 0;
}

//      Buffer Pool mgr

// find segment in pool
// must be called with hashslot idx locked
//      return NULL if not there
//      otherwise return node

BtPool *bt_findpool(BtDb *bt, uid page_no, uint idx)
{
BtPool *pool;
uint slot;

        // compute start of hash chain in pool

        if( slot = bt->mgr->hash[idx] ) 
                pool = bt->mgr->pool + slot;
        else
                return NULL;

        page_no &= ~bt->mgr->poolmask;

        while( pool->basepage != page_no )
          if( pool = pool->hashnext )
                continue;
          else
                return NULL;

        return pool;
}

// add segment to hash table

void bt_linkhash(BtDb *bt, BtPool *pool, uid page_no, int idx)
{
BtPool *node;
uint slot;

        pool->hashprev = pool->hashnext = NULL;
        pool->basepage = page_no & ~bt->mgr->poolmask;
        pool->lru = 1;

        if( slot = bt->mgr->hash[idx] ) {
                node = bt->mgr->pool + slot;
                pool->hashnext = node;
                node->hashprev = pool;
        }

        bt->mgr->hash[idx] = pool->slot;
}

//      find best segment to evict from buffer pool

BtPool *bt_findlru (BtDb *bt, uint hashslot)
{
unsigned long long int target = ~0LL;
BtPool *pool = NULL, *node;

        if( !hashslot )
                return NULL;

        node = bt->mgr->pool + hashslot;

        //  scan pool entries under hash table slot

        do {
          if( node->pin )
                continue;
          if( node->lru > target )
                continue;
          target = node->lru;
          pool = node;
        } while( node = node->hashnext );

        return pool;
}

//  map new buffer pool segment to virtual memory

BTERR bt_mapsegment(BtDb *bt, BtPool *pool, uid page_no)
{
off64_t off = (page_no & ~bt->mgr->poolmask) << bt->mgr->page_bits;
off64_t limit = off + ((bt->mgr->poolmask+1) << bt->mgr->page_bits);
int flag;

#ifdef unix
        flag = PROT_READ | ( bt->mgr->mode == BT_ro ? 0 : PROT_WRITE );
        pool->map = mmap (0, (bt->mgr->poolmask+1) << bt->mgr->page_bits, flag, MAP_SHARED | MAP_POPULATE, bt->mgr->idx, off);
        if( pool->map == MAP_FAILED )
                return bt->err = BTERR_map;
#else
        flag = ( bt->mgr->mode == BT_ro ? PAGE_READONLY : PAGE_READWRITE );
        pool->hmap = CreateFileMapping(bt->mgr->idx, NULL, flag, (DWORD)(limit >> 32), (DWORD)limit, NULL);
        if( !pool->hmap )
                return bt->err = BTERR_map;

        flag = ( bt->mgr->mode == BT_ro ? FILE_MAP_READ : FILE_MAP_WRITE );
        pool->map = MapViewOfFile(pool->hmap, flag, (DWORD)(off >> 32), (DWORD)off, (bt->mgr->poolmask+1) << bt->mgr->page_bits);
        if( !pool->map )
                return bt->err = BTERR_map;
#endif
        return bt->err = 0;
}

//      calculate page within pool

BtPage bt_page (BtDb *bt, BtPool *pool, uid page_no)
{
uint subpage = (uint)(page_no & bt->mgr->poolmask); // page within mapping
BtPage page;

        page = (BtPage)(pool->map + (subpage << bt->mgr->page_bits));
        return page;
}

//  release pool pin

void bt_unpinpool (BtPool *pool)
{
#ifdef unix
        __sync_fetch_and_add(&pool->pin, -1);
#else
        _InterlockedDecrement16 (&pool->pin);
#endif
}

//      find or place requested page in segment-pool
//      return pool table entry, incrementing pin

BtPool *bt_pinpool(BtDb *bt, uid page_no)
{
BtPool *pool, *node, *next;
uint slot, idx, victim;

        //      lock hash table chain

        idx = (uint)(page_no >> bt->mgr->seg_bits) % bt->mgr->hashsize;
        bt_spinreadlock (&bt->mgr->latch[idx]);

        //      look up in hash table

        if( pool = bt_findpool(bt, page_no, idx) ) {
#ifdef unix
                __sync_fetch_and_add(&pool->pin, 1);
#else
                _InterlockedIncrement16 (&pool->pin);
#endif
                bt_spinreleaseread (&bt->mgr->latch[idx]);
                pool->lru++;
                return pool;
        }

        //      upgrade to write lock

        bt_spinreleaseread (&bt->mgr->latch[idx]);
        bt_spinwritelock (&bt->mgr->latch[idx]);

        // try to find page in pool with write lock

        if( pool = bt_findpool(bt, page_no, idx) ) {
#ifdef unix
                __sync_fetch_and_add(&pool->pin, 1);
#else
                _InterlockedIncrement16 (&pool->pin);
#endif
                bt_spinreleasewrite (&bt->mgr->latch[idx]);
                pool->lru++;
                return pool;
        }

        // allocate a new pool node
        // and add to hash table

#ifdef unix
        slot = __sync_fetch_and_add(&bt->mgr->poolcnt, 1);
#else
        slot = _InterlockedIncrement16 (&bt->mgr->poolcnt) - 1;
#endif

        if( ++slot < bt->mgr->poolmax ) {
                pool = bt->mgr->pool + slot;
                pool->slot = slot;

                if( bt_mapsegment(bt, pool, page_no) )
                        return NULL;

                bt_linkhash(bt, pool, page_no, idx);
#ifdef unix
                __sync_fetch_and_add(&pool->pin, 1);
#else
                _InterlockedIncrement16 (&pool->pin);
#endif
                bt_spinreleasewrite (&bt->mgr->latch[idx]);
                return pool;
        }

        // pool table is full
        //      find best pool entry to evict

#ifdef unix
        __sync_fetch_and_add(&bt->mgr->poolcnt, -1);
#else
        _InterlockedDecrement16 (&bt->mgr->poolcnt);
#endif

        while( 1 ) {
#ifdef unix
                victim = __sync_fetch_and_add(&bt->mgr->evicted, 1);
#else
                victim = _InterlockedIncrement (&bt->mgr->evicted) - 1;
#endif
                victim %= bt->mgr->hashsize;

                // try to get write lock
                //      skip entry if not obtained

                if( !bt_spinwritetry (&bt->mgr->latch[victim]) )
                        continue;

                //  if pool entry is empty
                //      or any pages are pinned
                //      skip this entry

                if( !(pool = bt_findlru(bt, bt->mgr->hash[victim])) ) {
                        bt_spinreleasewrite (&bt->mgr->latch[victim]);
                        continue;
                }

                // unlink victim pool node from hash table

                if( node = pool->hashprev )
                        node->hashnext = pool->hashnext;
                else if( node = pool->hashnext )
                        bt->mgr->hash[victim] = node->slot;
                else
                        bt->mgr->hash[victim] = 0;

                if( node = pool->hashnext )
                        node->hashprev = pool->hashprev;

                bt_spinreleasewrite (&bt->mgr->latch[victim]);

                //      remove old file mapping
#ifdef unix
                munmap (pool->map, (bt->mgr->poolmask+1) << bt->mgr->page_bits);
#else
                FlushViewOfFile(pool->map, 0);
                UnmapViewOfFile(pool->map);
                CloseHandle(pool->hmap);
#endif
                pool->map = NULL;

                //  create new pool mapping
                //  and link into hash table

                if( bt_mapsegment(bt, pool, page_no) )
                        return NULL;

                bt_linkhash(bt, pool, page_no, idx);
#ifdef unix
                __sync_fetch_and_add(&pool->pin, 1);
#else
                _InterlockedIncrement16 (&pool->pin);
#endif
                bt_spinreleasewrite (&bt->mgr->latch[idx]);
                return pool;
        }
}

// place write, read, or parent lock on requested page_no.

void bt_lockpage(BtLock mode, BtLatchSet *set)
{
        switch( mode ) {
        case BtLockRead:
                bt_readlock (set->readwr);
                break;
        case BtLockWrite:
                bt_writelock (set->readwr);
                break;
        case BtLockAccess:
                bt_readlock (set->access);
                break;
        case BtLockDelete:
                bt_writelock (set->access);
                break;
        case BtLockParent:
                bt_writelock (set->parent);
                break;
        }
}

// remove write, read, or parent lock on requested page

void bt_unlockpage(BtLock mode, BtLatchSet *set)
{
        switch( mode ) {
        case BtLockRead:
                bt_releaseread (set->readwr);
                break;
        case BtLockWrite:
                bt_releasewrite (set->readwr);
                break;
        case BtLockAccess:
                bt_releaseread (set->access);
                break;
        case BtLockDelete:
                bt_releasewrite (set->access);
                break;
        case BtLockParent:
                bt_releasewrite (set->parent);
                break;
        }
}

//      allocate a new page and write page into it

uid bt_newpage(BtDb *bt, BtPage page)
{
BtPageSet set[1];
uid new_page;
int reuse;

        //      lock allocation page

        bt_spinwritelock(bt->mgr->latchmgr->lock);

        // use empty chain first
        // else allocate empty page

        if( new_page = bt_getid(bt->mgr->latchmgr->alloc[1].right) ) {
                if( set->pool = bt_pinpool (bt, new_page) )
                        set->page = bt_page (bt, set->pool, new_page);
                else
                        return 0;

                bt_putid(bt->mgr->latchmgr->alloc[1].right, bt_getid(set->page->right));
                bt_unpinpool (set->pool);
                reuse = 1;
        } else {
                new_page = bt_getid(bt->mgr->latchmgr->alloc->right);
                bt_putid(bt->mgr->latchmgr->alloc->right, new_page+1);
                reuse = 0;
        }
#ifdef unix
        if ( pwrite(bt->mgr->idx, page, bt->mgr->page_size, new_page << bt->mgr->page_bits) < bt->mgr->page_size )
                return bt->err = BTERR_wrt, 0;

        // if writing first page of pool block, zero last page in the block

        if ( !reuse && bt->mgr->poolmask > 0 && (new_page & bt->mgr->poolmask) == 0 )
        {
                // use zero buffer to write zeros
                if ( pwrite(bt->mgr->idx,bt->zero, bt->mgr->page_size, (new_page | bt->mgr->poolmask) << bt->mgr->page_bits) < bt->mgr->page_size )
                        return bt->err = BTERR_wrt, 0;
        }
#else
        //      bring new page into pool and copy page.
        //      this will extend the file into the new pages.

        if( set->pool = bt_pinpool (bt, new_page) )
                set->page = bt_page (bt, set->pool, new_page);
        else
                return 0;

        memcpy(set->page, page, bt->mgr->page_size);
        bt_unpinpool (set->pool);
#endif
        // unlock allocation latch and return new page no

        bt_spinreleasewrite(bt->mgr->latchmgr->lock);
        return new_page;
}

//  find slot in page for given key at a given level

int bt_findslot (BtPageSet *set, unsigned char *key, uint len)
{
uint diff, higher = set->page->cnt, low = 1, slot;

        //        make stopper key an infinite fence value

        if( bt_getid (set->page->right) )
                higher++;

        //      low is the lowest candidate.
        //  loop ends when they meet

        //  higher is already
        //      tested as .ge. the given key.

        while( diff = higher - low ) {
                slot = low + ( diff >> 1 );
                if( keycmp (keyptr(set->page, slot), key, len) < 0 )
                        low = slot + 1;
                else
                        higher = slot;
        }

        if( higher <= set->page->cnt )
                return higher;

        //      if leaf page, compare against fence value

        //      return zero if key is on right link page
        //      or return slot beyond last key

        if( set->page->lvl || keycmp ((BtKey)set->page->fence, key, len) < 0 )
                return 0;

        return higher;
}

//  find and load page at given level for given key
//      leave page rd or wr locked as requested

int bt_loadpage (BtDb *bt, BtPageSet *set, unsigned char *key, uint len, uint lvl, uint lock)
{
uid page_no = ROOT_page, prevpage = 0;
uint drill = 0xff, slot;
BtLatchSet *prevlatch;
uint mode, prevmode;
BtPool *prevpool;

  //  start at root of btree and drill down

  do {
        // determine lock mode of drill level
        mode = (lock == BtLockWrite) && (drill == lvl) ? BtLockWrite : BtLockRead; 

        set->latch = bt_pinlatch (bt, page_no);
        set->page_no = page_no;

        // pin page contents

        if( set->pool = bt_pinpool (bt, page_no) )
                set->page = bt_page (bt, set->pool, page_no);
        else
                return 0;

        // obtain access lock using lock chaining with Access mode

        if( page_no > ROOT_page )
          bt_lockpage(BtLockAccess, set->latch);

        //      release & unpin parent page

        if( prevpage ) {
          bt_unlockpage(prevmode, prevlatch);
          bt_unpinlatch (prevlatch);
          bt_unpinpool (prevpool);
          prevpage = 0;
        }

        // obtain read lock using lock chaining

        bt_lockpage(mode, set->latch);

        if( page_no > ROOT_page )
          bt_unlockpage(BtLockAccess, set->latch);

        // re-read and re-lock root after determining actual level of root

        if( set->page->lvl != drill) {
                if ( set->page_no != ROOT_page )
                        return bt->err = BTERR_struct, 0;
                        
                drill = set->page->lvl;

                if( lock == BtLockWrite && drill == lvl ) {
                  bt_unlockpage(mode, set->latch);
                  bt_unpinlatch (set->latch);
                  bt_unpinpool (set->pool);
                  continue;
                }
        }

        prevpage = set->page_no;
        prevlatch = set->latch;
        prevpool = set->pool;
        prevmode = mode;

        //      if page is being deleted and we should continue right

        if( set->page->kill && set->page->goright ) {
                page_no = bt_getid (set->page->right);
                continue;
        }

        //      otherwise, wait for deleted node to clear

        if( set->page->kill ) {
                bt_unlockpage(mode, set->latch);
                bt_unpinlatch (set->latch);
                bt_unpinpool (set->pool);
                page_no = ROOT_page;
                prevpage = 0;
                drill = 0xff;
#ifdef unix
                sched_yield();
#else
                SwitchToThread();
#endif
                continue;
        }
        
        //  find key on page at this level
        //  and descend to requested level

        if( slot = bt_findslot (set, key, len) ) {
          if( drill == lvl )
                return slot;

          if( slot > set->page->cnt )
                return bt->err = BTERR_struct;

          while( slotptr(set->page, slot)->dead )
                if( slot++ < set->page->cnt )
                        continue;
                else
                        return bt->err = BTERR_struct, 0;

          page_no = bt_getid(slotptr(set->page, slot)->id);
          drill--;
          continue;
        }

        //  or slide right into next page

        page_no = bt_getid(set->page->right);

  } while( page_no );

  // return error on end of right chain

  bt->err = BTERR_struct;
  return 0;     // return error
}

// drill down fixing fence values for left sibling tree

//  call with set write locked
//      return with set unlocked & unpinned.

BTERR bt_fixfences (BtDb *bt, BtPageSet *set, unsigned char *newfence)
{
unsigned char oldfence[256];
BtPageSet next[1];
int chk;

  memcpy (oldfence, set->page->fence, 256);

  while( !set->page->kill && set->page->lvl ) {
        next->page_no = bt_getid(slotptr(set->page, set->page->cnt)->id);
        next->latch = bt_pinlatch (bt, next->page_no);
        bt_lockpage (BtLockParent, next->latch);
        bt_lockpage (BtLockAccess, next->latch);
        bt_lockpage (BtLockWrite, next->latch);
        bt_unlockpage (BtLockAccess, next->latch);

        if( next->pool = bt_pinpool (bt, next->page_no) )
                next->page = bt_page (bt, next->pool, next->page_no);
        else
                return bt->err;

        chk = keycmp ((BtKey)next->page->fence, oldfence + 1, *oldfence);

        if( chk < 0 ) {
          next->page_no = bt_getid (next->page->right);
          bt_unlockpage (BtLockWrite, next->latch);
          bt_unlockpage (BtLockParent, next->latch);
          bt_unpinlatch (next->latch);
          bt_unpinpool (next->pool);
          continue;
        }

        if( chk > 0 )
                return bt->err = BTERR_struct;

        if( bt_fixfences (bt, next, newfence) )
                return bt->err;

        break;
  }

  memcpy (set->page->fence, newfence, 256);

  bt_unlockpage (BtLockWrite, set->latch);
  bt_unlockpage (BtLockParent, set->latch);
  bt_unpinlatch (set->latch);
  bt_unpinpool (set->pool);
  return 0;
}

//      return page to free list
//      page must be delete & write locked

void bt_freepage (BtDb *bt, BtPageSet *set)
{
        //      lock allocation page

        bt_spinwritelock (bt->mgr->latchmgr->lock);

        //      store chain in second right
        bt_putid(set->page->right, bt_getid(bt->mgr->latchmgr->alloc[1].right));
        bt_putid(bt->mgr->latchmgr->alloc[1].right, set->page_no);
        set->page->free = 1;

        // unlock released page

        bt_unlockpage (BtLockDelete, set->latch);
        bt_unlockpage (BtLockWrite, set->latch);
        bt_unpinlatch (set->latch);
        bt_unpinpool (set->pool);

        // unlock allocation page

        bt_spinreleasewrite (bt->mgr->latchmgr->lock);
}

//      remove the root level by promoting its only child
//      call with parent and child pages

BTERR bt_removeroot (BtDb *bt, BtPageSet *root, BtPageSet *child)
{
uid next = 0;

  do {
        if( next ) {
          child->latch = bt_pinlatch (bt, next);
          bt_lockpage (BtLockDelete, child->latch);
          bt_lockpage (BtLockWrite, child->latch);

          if( child->pool = bt_pinpool (bt, next) )
                child->page = bt_page (bt, child->pool, next);
          else
                return bt->err;

          child->page_no = next;
        }

        memcpy (root->page, child->page, bt->mgr->page_size);
        next = bt_getid (slotptr(child->page, child->page->cnt)->id);
        bt_freepage (bt, child);
  } while( root->page->lvl > 1 && root->page->cnt == 1 );

  bt_unlockpage (BtLockWrite, root->latch);
  bt_unpinlatch (root->latch);
  bt_unpinpool (root->pool);
  return 0;
}

//  pull right page over ourselves in simple merge

BTERR bt_mergeright (BtDb *bt, BtPageSet *set, BtPageSet *parent, BtPageSet *right, uint slot, uint idx)
{
        //  install ourselves as child page
        //      and delete ourselves from parent

        bt_putid (slotptr(parent->page, idx)->id, set->page_no);
        slotptr(parent->page, slot)->dead = 1;
        parent->page->act--;

        //      collapse any empty slots

        while( idx = parent->page->cnt - 1 )
          if( slotptr(parent->page, idx)->dead ) {
                *slotptr(parent->page, idx) = *slotptr(parent->page, idx + 1);
                memset (slotptr(parent->page, parent->page->cnt--), 0, sizeof(BtSlot));
          } else
                  break;

        memcpy (set->page, right->page, bt->mgr->page_size);
        bt_unlockpage (BtLockParent, right->latch);

        bt_freepage (bt, right);

        //      do we need to remove a btree level?
        //      (leave the first page of leaves alone)

        if( parent->page_no == ROOT_page && parent->page->cnt == 1 )
          if( set->page->lvl )
                return bt_removeroot (bt, parent, set);

        bt_unlockpage (BtLockWrite, parent->latch);
        bt_unlockpage (BtLockDelete, set->latch);
        bt_unlockpage (BtLockWrite, set->latch);
        bt_unpinlatch (parent->latch);
        bt_unpinpool (parent->pool);
        bt_unpinlatch (set->latch);
        bt_unpinpool (set->pool);
        return 0;
}

//      remove both child and parent from the btree
//      from the fence position in the parent
//      call with both pages locked for writing

BTERR bt_removeparent (BtDb *bt, BtPageSet *child, BtPageSet *parent, BtPageSet *right, BtPageSet *rparent, uint lvl)
{
unsigned char pagefence[256];
uint idx;

        //  pull right sibling over ourselves and unlock

        memcpy (child->page, right->page, bt->mgr->page_size);

        bt_unlockpage (BtLockWrite, child->latch);
        bt_unpinlatch (child->latch);
        bt_unpinpool (child->pool);

        //  install ourselves into right link of old right page

        bt_putid (right->page->right, child->page_no);
        right->page->goright = 1;       // tell bt_loadpage to go right to us
        right->page->kill = 1;

        bt_unlockpage (BtLockWrite, right->latch);

        //      remove our slot from our parent
        //      signal to move right

        parent->page->goright = 1;      // tell bt_loadpage to go right to rparent
        parent->page->kill = 1;
        parent->page->act--;

        //      redirect right page pointer in right parent to us

        for( idx = 0; idx++ < rparent->page->cnt; )
          if( !slotptr(rparent->page, idx)->dead )
                break;

        if( bt_getid (slotptr(rparent->page, idx)->id) != right->page_no )
                return bt->err = BTERR_struct;

        bt_putid (slotptr(rparent->page, idx)->id, child->page_no);
        bt_unlockpage (BtLockWrite, rparent->latch);
        bt_unpinlatch (rparent->latch);
        bt_unpinpool (rparent->pool);

        //      free the right page

        bt_lockpage (BtLockDelete, right->latch);
        bt_lockpage (BtLockWrite, right->latch);
        bt_freepage (bt, right);

        //      save parent page fence value

        memcpy (pagefence, parent->page->fence, 256);
        bt_unlockpage (BtLockWrite, parent->latch);

        return bt_removepage (bt, parent, lvl, pagefence);
}

//      remove page from btree
//      call with page unlocked
//      returns with page on free list

BTERR bt_removepage (BtDb *bt, BtPageSet *set, uint lvl, unsigned char *pagefence)
{
BtPageSet parent[1], sibling[1], rparent[1];
unsigned char newfence[256];
uint slot, idx;
BtKey ptr;

        //      load and lock our parent

retry:
        if( !(slot = bt_loadpage (bt, parent, pagefence+1, *pagefence, lvl+1, BtLockWrite)) )
                return bt->err;

        //      can we do a simple merge entirely
        //      between siblings on the parent page?

        if( slot < parent->page->cnt ) {
                // find our right neighbor
                //      right must exist because the stopper prevents
                //      the rightmost page from deleting

                for( idx = slot; idx++ < parent->page->cnt; )
                  if( !slotptr(parent->page, idx)->dead )
                        break;

                sibling->page_no = bt_getid (slotptr (parent->page, idx)->id);

                bt_lockpage (BtLockDelete, set->latch);
                bt_lockpage (BtLockWrite, set->latch);

                //      merge right if sibling shows up in
                //  our parent and is not being killed

                if( sibling->page_no == bt_getid (set->page->right) ) {
                  sibling->latch = bt_pinlatch (bt, sibling->page_no);
                  bt_lockpage (BtLockParent, sibling->latch);
                  bt_lockpage (BtLockDelete, sibling->latch);
                  bt_lockpage (BtLockWrite, sibling->latch);

                  if( sibling->pool = bt_pinpool (bt, sibling->page_no) )
                        sibling->page = bt_page (bt, sibling->pool, sibling->page_no);
                  else
                        return bt->err;

                  if( !sibling->page->kill )
                        return bt_mergeright(bt, set, parent, sibling, slot, idx);

                  //  try again later

                  bt_unlockpage (BtLockWrite, sibling->latch);
                  bt_unlockpage (BtLockParent, sibling->latch);
                  bt_unlockpage (BtLockDelete, sibling->latch);
                  bt_unpinlatch (sibling->latch);
                  bt_unpinpool (sibling->pool);
                }

                bt_unlockpage (BtLockDelete, set->latch);
                bt_unlockpage (BtLockWrite, set->latch);
                bt_unlockpage (BtLockWrite, parent->latch);
                bt_unpinlatch (parent->latch);
                bt_unpinpool (parent->pool);
#ifdef linux
                sched_yield();
#else
                SwitchToThread();
#endif
                goto retry;
        }

        //  find our left neighbor in our parent page

        for( idx = slot; --idx; )
          if( !slotptr(parent->page, idx)->dead )
                break;

        //      if no left neighbor, delete ourselves and our parent

        if( !idx ) {
                bt_lockpage (BtLockAccess, set->latch);
                bt_lockpage (BtLockWrite, set->latch);
                bt_unlockpage (BtLockAccess, set->latch);

                rparent->page_no = bt_getid (parent->page->right);
                rparent->latch = bt_pinlatch (bt, rparent->page_no);

                bt_lockpage (BtLockAccess, rparent->latch);
                bt_lockpage (BtLockWrite, rparent->latch);
                bt_unlockpage (BtLockAccess, rparent->latch);

                if( rparent->pool = bt_pinpool (bt, rparent->page_no) )
                        rparent->page = bt_page (bt, rparent->pool, rparent->page_no);
                else
                        return bt->err;

                if( !rparent->page->kill ) {
                  sibling->page_no = bt_getid (set->page->right);
                  sibling->latch = bt_pinlatch (bt, sibling->page_no);

                  bt_lockpage (BtLockAccess, sibling->latch);
                  bt_lockpage (BtLockWrite, sibling->latch);
                  bt_unlockpage (BtLockAccess, sibling->latch);

                  if( sibling->pool = bt_pinpool (bt, sibling->page_no) )
                        sibling->page = bt_page (bt, sibling->pool, sibling->page_no);
                  else
                        return bt->err;

                  if( !sibling->page->kill )
                        return bt_removeparent (bt, set, parent, sibling, rparent, lvl+1);

                  //  try again later

                  bt_unlockpage (BtLockWrite, sibling->latch);
                  bt_unpinlatch (sibling->latch);
                  bt_unpinpool (sibling->pool);
                }

                bt_unlockpage (BtLockWrite, set->latch);
                bt_unlockpage (BtLockWrite, rparent->latch);
                bt_unpinlatch (rparent->latch);
                bt_unpinpool (rparent->pool);

                bt_unlockpage (BtLockWrite, parent->latch);
                bt_unpinlatch (parent->latch);
                bt_unpinpool (parent->pool);
#ifdef linux
                sched_yield();
#else
                SwitchToThread();
#endif
                goto retry;
        }

        // redirect parent to our left sibling
        // lock and map our left sibling's page

        sibling->page_no = bt_getid (slotptr(parent->page, idx)->id);
        sibling->latch = bt_pinlatch (bt, sibling->page_no);

        //      wait our turn on fence key maintenance

        bt_lockpage(BtLockParent, sibling->latch);
        bt_lockpage(BtLockAccess, sibling->latch);
        bt_lockpage(BtLockWrite, sibling->latch);
        bt_unlockpage(BtLockAccess, sibling->latch);

        if( sibling->pool = bt_pinpool (bt, sibling->page_no) )
                sibling->page = bt_page (bt, sibling->pool, sibling->page_no);
        else
                return bt->err;

        //  wait until left sibling is in our parent

        if( bt_getid (sibling->page->right) != set->page_no ) {
                bt_unlockpage (BtLockWrite, parent->latch);
                bt_unlockpage (BtLockWrite, sibling->latch);
                bt_unlockpage (BtLockParent, sibling->latch);
                bt_unpinlatch (parent->latch);
                bt_unpinpool (parent->pool);
                bt_unpinlatch (sibling->latch);
                bt_unpinpool (sibling->pool);
#ifdef linux
                sched_yield();
#else
                SwitchToThread();
#endif
                goto retry;
        }

        //      delete our left sibling from parent

        slotptr(parent->page,idx)->dead = 1;
        parent->page->dirty = 1;
        parent->page->act--;

        //      redirect our parent slot to our left sibling

        bt_putid (slotptr(parent->page, slot)->id, sibling->page_no);
        memcpy (sibling->page->right, set->page->right, BtId);

        //      collapse dead slots from parent

        while( idx = parent->page->cnt - 1 )
          if( slotptr(parent->page, idx)->dead ) {
                *slotptr(parent->page, idx) = *slotptr(parent->page, parent->page->cnt);
                memset (slotptr(parent->page, parent->page->cnt--), 0, sizeof(BtSlot));
          } else
                  break;

        //  free our original page

        bt_lockpage (BtLockDelete, set->latch);
        bt_lockpage (BtLockWrite, set->latch);
        bt_freepage (bt, set);

        //      go down the left node's fence keys to the leaf level
        //      and update the fence keys in each page

        memcpy (newfence, parent->page->fence, 256);

        if( bt_fixfences (bt, sibling, newfence) )
                return bt->err;

        //  promote sibling as new root?

        if( parent->page_no == ROOT_page && parent->page->cnt == 1 )
         if( sibling->page->lvl ) {
          sibling->latch = bt_pinlatch (bt, sibling->page_no);
          bt_lockpage (BtLockDelete, sibling->latch);
          bt_lockpage (BtLockWrite, sibling->latch);

          if( sibling->pool = bt_pinpool (bt, sibling->page_no) )
                sibling->page = bt_page (bt, sibling->pool, sibling->page_no);
          else
                return bt->err;

          return bt_removeroot (bt, parent, sibling);
         }

        bt_unlockpage (BtLockWrite, parent->latch);
        bt_unpinlatch (parent->latch);
        bt_unpinpool (parent->pool);

        return 0;
}

//  find and delete key on page by marking delete flag bit
//  if page becomes empty, delete it from the btree

BTERR bt_deletekey (BtDb *bt, unsigned char *key, uint len)
{
unsigned char pagefence[256];
uint slot, idx, found;
BtPageSet set[1];
BtKey ptr;

        if( slot = bt_loadpage (bt, set, key, len, 0, BtLockWrite) )
                ptr = keyptr(set->page, slot);
        else
                return bt->err;

        // if key is found delete it, otherwise ignore request

        if( found = slot <= set->page->cnt )
          if( found = !keycmp (ptr, key, len) )
                if( found = slotptr(set->page, slot)->dead == 0 ) {
                  slotptr(set->page,slot)->dead = 1;
                  set->page->dirty = 1;
                  set->page->act--;

                  // collapse empty slots

                  while( idx = set->page->cnt - 1 )
                        if( slotptr(set->page, idx)->dead ) {
                          *slotptr(set->page, idx) = *slotptr(set->page, idx + 1);
                          memset (slotptr(set->page, set->page->cnt--), 0, sizeof(BtSlot));
                        } else
                                break;
                }

        if( set->page->act ) {
                bt_unlockpage(BtLockWrite, set->latch);
                bt_unpinlatch (set->latch);
                bt_unpinpool (set->pool);
                return bt->found = found, 0;
        }

        memcpy (pagefence, set->page->fence, 256);
        set->page->kill = 1;

        bt_unlockpage (BtLockWrite, set->latch);

        if( bt_removepage (bt, set, 0, pagefence) )
                return bt->err;

        bt->found = found;
        return 0;
}

//      find key in leaf level and return row-id

uid bt_findkey (BtDb *bt, unsigned char *key, uint len)
{
BtPageSet set[1];
uint  slot;
BtKey ptr;
uid id;

        if( slot = bt_loadpage (bt, set, key, len, 0, BtLockRead) )
                ptr = keyptr(set->page, slot);
        else
                return 0;

        // if key exists, return row-id
        //      otherwise return 0

        if( !keycmp (ptr, key, len) )
                id = bt_getid(slotptr(set->page,slot)->id);
        else
                id = 0;

        bt_unlockpage (BtLockRead, set->latch);
        bt_unpinlatch (set->latch);
        bt_unpinpool (set->pool);
        return id;
}

//      check page for space available,
//      clean if necessary and return
//      0 - page needs splitting
//      >0  new slot value

uint bt_cleanpage(BtDb *bt, BtPage page, uint amt, uint slot)
{
uint nxt = bt->mgr->page_size, off;
uint cnt = 0, idx = 0;
uint max = page->cnt;
uint newslot = max;
BtKey key;

        if( page->min >= (max+1) * sizeof(BtSlot) + sizeof(*page) + amt + 1 )
                return slot;

        //      skip cleanup if nothing to reclaim

        if( !page->dirty )
                return 0;

        memcpy (bt->frame, page, bt->mgr->page_size);

        // skip page info and set rest of page to zero

        memset (page+1, 0, bt->mgr->page_size - sizeof(*page));
        page->dirty = 0;
        page->act = 0;

        // try cleaning up page first
        // by removing deleted keys

        while( cnt++ < max ) {
                if( cnt == slot )
                        newslot = idx + 1;
                if( slotptr(bt->frame,cnt)->dead )
                        continue;

                // if its not the fence key,
                // copy the key across

                off = slotptr(bt->frame,cnt)->off;

                if( off >= sizeof(*page) ) {
                        key = keyptr(bt->frame, cnt);
                        off = nxt -= key->len + 1;
                        memcpy ((unsigned char *)page + nxt, key, key->len + 1);
                }

                // copy slot

                memcpy(slotptr(page, ++idx)->id, slotptr(bt->frame, cnt)->id, BtId);
                slotptr(page, idx)->tod = slotptr(bt->frame, cnt)->tod;
                slotptr(page, idx)->off = off;
                page->act++;
        }

        page->min = nxt;
        page->cnt = idx;

        //      see if page has enough space now, or does it need splitting?

        if( page->min >= (idx+1) * sizeof(BtSlot) + sizeof(*page) + amt + 1 )
                return newslot;

        return 0;
}

// split the root and raise the height of the btree

BTERR bt_splitroot(BtDb *bt, BtPageSet *root, uid page_no2)
{
uint nxt = bt->mgr->page_size;
unsigned char leftkey[256];
uid new_page;

        //  Obtain an empty page to use, and copy the current
        //  root contents into it, e.g. lower keys

        memcpy (leftkey, root->page->fence, 256);
        root->page->posted = 1;

        if( !(new_page = bt_newpage(bt, root->page)) )
                return bt->err;

        // preserve the page info at the bottom
        // of higher keys and set rest to zero

        memset(root->page+1, 0, bt->mgr->page_size - sizeof(*root->page));
        memset(root->page->fence, 0, 256);
        root->page->fence[0] = 2;
        root->page->fence[1] = 0xff;
        root->page->fence[2] = 0xff;

        // insert lower keys page fence key on newroot page

        nxt -= *leftkey + 1;
        memcpy ((unsigned char *)root->page + nxt, leftkey, *leftkey + 1);
        bt_putid(slotptr(root->page, 1)->id, new_page);
        slotptr(root->page, 1)->off = nxt;
        
        // insert stopper key on newroot page
        // and increase the root height

        bt_putid(slotptr(root->page, 2)->id, page_no2);
        slotptr(root->page, 2)->off = offsetof(struct BtPage_, fence);

        bt_putid(root->page->right, 0);
        root->page->min = nxt;          // reset lowest used offset and key count
        root->page->cnt = 2;
        root->page->act = 2;
        root->page->lvl++;

        // release and unpin root

        bt_unlockpage(BtLockWrite, root->latch);
        bt_unpinlatch (root->latch);
        bt_unpinpool (root->pool);
        return 0;
}

//  split already locked full node
//      return unlocked.

BTERR bt_splitpage (BtDb *bt, BtPageSet *set)
{
uint cnt = 0, idx = 0, max, nxt = bt->mgr->page_size, off;
unsigned char fencekey[256];
uint lvl = set->page->lvl;
uid right;
BtKey key;

        //  split higher half of keys to bt->frame

        memset (bt->frame, 0, bt->mgr->page_size);
        max = set->page->cnt;
        cnt = max / 2;
        idx = 0;

        while( cnt++ < max ) {
                if( !lvl || cnt < max ) {
                        key = keyptr(set->page, cnt);
                        off = nxt -= key->len + 1;
                        memcpy ((unsigned char *)bt->frame + nxt, key, key->len + 1);
                } else
                        off = offsetof(struct BtPage_, fence);

                memcpy(slotptr(bt->frame,++idx)->id, slotptr(set->page,cnt)->id, BtId);
                slotptr(bt->frame, idx)->tod = slotptr(set->page, cnt)->tod;
                slotptr(bt->frame, idx)->off = off;
                bt->frame->act++;
        }

        if( set->page_no == ROOT_page )
                bt->frame->posted = 1;

        memcpy (bt->frame->fence, set->page->fence, 256);
        bt->frame->bits = bt->mgr->page_bits;
        bt->frame->min = nxt;
        bt->frame->cnt = idx;
        bt->frame->lvl = lvl;

        // link right node

        if( set->page_no > ROOT_page )
                memcpy (bt->frame->right, set->page->right, BtId);

        //      get new free page and write higher keys to it.

        if( !(right = bt_newpage(bt, bt->frame)) )
                return bt->err;

        //      update lower keys to continue in old page

        memcpy (bt->frame, set->page, bt->mgr->page_size);
        memset (set->page+1, 0, bt->mgr->page_size - sizeof(*set->page));
        nxt = bt->mgr->page_size;
        set->page->posted = 0;
        set->page->dirty = 0;
        set->page->act = 0;
        cnt = 0;
        idx = 0;

        //  assemble page of smaller keys

        while( cnt++ < max / 2 ) {
                key = keyptr(bt->frame, cnt);

                if( !lvl || cnt < max / 2 ) {
                        off = nxt -= key->len + 1;
                        memcpy ((unsigned char *)set->page + nxt, key, key->len + 1);
                } else 
                        off = offsetof(struct BtPage_, fence);

                memcpy(slotptr(set->page,++idx)->id, slotptr(bt->frame,cnt)->id, BtId);
                slotptr(set->page, idx)->tod = slotptr(bt->frame, cnt)->tod;
                slotptr(set->page, idx)->off = off;
                set->page->act++;
        }

        // install fence key for smaller key page

        memset(set->page->fence, 0, 256);
        memcpy(set->page->fence, key, key->len + 1);

        bt_putid(set->page->right, right);
        set->page->min = nxt;
        set->page->cnt = idx;

        // if current page is the root page, split it

        if( set->page_no == ROOT_page )
                return bt_splitroot (bt, set, right);

        bt_unlockpage (BtLockWrite, set->latch);

        // insert new fences in their parent pages

        while( 1 ) {
                bt_lockpage (BtLockParent, set->latch);
                bt_lockpage (BtLockWrite, set->latch);

                memcpy (fencekey, set->page->fence, 256);
                right = bt_getid (set->page->right);

                if( set->page->posted ) {
                        bt_unlockpage (BtLockParent, set->latch);
                        bt_unlockpage (BtLockWrite, set->latch);
                        bt_unpinlatch (set->latch);
                        bt_unpinpool (set->pool);
                        return 0;
                }

                set->page->posted = 1;
                bt_unlockpage (BtLockWrite, set->latch);

                if( bt_insertkey (bt, fencekey+1, *fencekey, set->page_no, time(NULL), lvl+1) )
                        return bt->err;

                bt_unlockpage (BtLockParent, set->latch);
                bt_unpinlatch (set->latch);
                bt_unpinpool (set->pool);

                if( !(set->page_no = right) )
                        break;

                set->latch = bt_pinlatch (bt, right);

                if( set->pool = bt_pinpool (bt, right) )
                        set->page = bt_page (bt, set->pool, right);
                else
                        return bt->err;
        }

        return 0;
}

//  Insert new key into the btree at given level.

BTERR bt_insertkey (BtDb *bt, unsigned char *key, uint len, uid id, uint tod, uint lvl)
{
BtPageSet set[1];
uint slot, idx;
BtKey ptr;

        while( 1 ) {
                if( slot = bt_loadpage (bt, set, key, len, lvl, BtLockWrite) )
                        ptr = keyptr(set->page, slot);
                else
                {
                        if ( !bt->err )
                                bt->err = BTERR_ovflw;
                        return bt->err;
                }

                // if key already exists, update id and return

                if( slot <= set->page->cnt )
                  if( !keycmp (ptr, key, len) ) {
                        if( slotptr(set->page, slot)->dead )
                                set->page->act++;
                        slotptr(set->page, slot)->dead = 0;
                        slotptr(set->page, slot)->tod = tod;
                        bt_putid(slotptr(set->page,slot)->id, id);
                        bt_unlockpage(BtLockWrite, set->latch);
                        bt_unpinlatch (set->latch);
                        bt_unpinpool (set->pool);
                        return 0;
                }

                // check if page has enough space

                if( slot = bt_cleanpage (bt, set->page, len, slot) )
                        break;

                if( bt_splitpage (bt, set) )
                        return bt->err;
        }

        // calculate next available slot and copy key into page

        set->page->min -= len + 1; // reset lowest used offset
        ((unsigned char *)set->page)[set->page->min] = len;
        memcpy ((unsigned char *)set->page + set->page->min +1, key, len );

        for( idx = slot; idx <= set->page->cnt; idx++ )
          if( slotptr(set->page, idx)->dead )
                break;

        // now insert key into array before slot

        if( idx > set->page->cnt )
                set->page->cnt++;

        set->page->act++;

        while( idx > slot )
                *slotptr(set->page, idx) = *slotptr(set->page, idx -1), idx--;

        bt_putid(slotptr(set->page,slot)->id, id);
        slotptr(set->page, slot)->off = set->page->min;
        slotptr(set->page, slot)->tod = tod;
        slotptr(set->page, slot)->dead = 0;

        bt_unlockpage (BtLockWrite, set->latch);
        bt_unpinlatch (set->latch);
        bt_unpinpool (set->pool);
        return 0;
}

//  cache page of keys into cursor and return starting slot for given key

uint bt_startkey (BtDb *bt, unsigned char *key, uint len)
{
BtPageSet set[1];
uint slot;

        // cache page for retrieval

        if( slot = bt_loadpage (bt, set, key, len, 0, BtLockRead) )
          memcpy (bt->cursor, set->page, bt->mgr->page_size);
        else
          return 0;

        bt->cursor_page = set->page_no;

        bt_unlockpage(BtLockRead, set->latch);
        bt_unpinlatch (set->latch);
        bt_unpinpool (set->pool);
        return slot;
}

//  return next slot for cursor page
//  or slide cursor right into next page

uint bt_nextkey (BtDb *bt, uint slot)
{
BtPageSet set[1];
uid right;

  do {
        right = bt_getid(bt->cursor->right);
        while( slot++ < bt->cursor->cnt )
          if( slotptr(bt->cursor,slot)->dead )
                continue;
          else if( right || (slot < bt->cursor->cnt) ) // skip infinite stopper
                return slot;
          else
                break;

        if( !right )
                break;

        bt->cursor_page = right;

        if( set->pool = bt_pinpool (bt, right) )
                set->page = bt_page (bt, set->pool, right);
        else
                return 0;

        set->latch = bt_pinlatch (bt, right);
    bt_lockpage(BtLockRead, set->latch);

        memcpy (bt->cursor, set->page, bt->mgr->page_size);

        bt_unlockpage(BtLockRead, set->latch);
        bt_unpinlatch (set->latch);
        bt_unpinpool (set->pool);
        slot = 0;
  } while( 1 );

  return bt->err = 0;
}

BtKey bt_key(BtDb *bt, uint slot)
{
        return keyptr(bt->cursor, slot);
}

uid bt_uid(BtDb *bt, uint slot)
{
        return bt_getid(slotptr(bt->cursor,slot)->id);
}

uint bt_tod(BtDb *bt, uint slot)
{
        return slotptr(bt->cursor,slot)->tod;
}


#ifdef STANDALONE

void bt_latchaudit (BtDb *bt)
{
ushort idx, hashidx;
BtPageSet set[1];

#ifdef unix
        for( idx = 1; idx < bt->mgr->latchmgr->latchdeployed; idx++ ) {
                set->latch = bt->mgr->latchsets + idx;
                if( set->latch->pin ) {
                        fprintf(stderr, "latchset %d pinned for page %.6x\n", idx, set->latch->page_no);
                        set->latch->pin = 0;
                }
        }

        for( hashidx = 0; hashidx < bt->mgr->latchmgr->latchhash; hashidx++ ) {
          if( idx = bt->mgr->latchmgr->table[hashidx].slot ) do {
                set->latch = bt->mgr->latchsets + idx;
                if( set->latch->hash != hashidx )
                        fprintf(stderr, "latchset %d wrong hashidx\n", idx);
                if( set->latch->pin )
                        fprintf(stderr, "latchset %d pinned for page %.8x\n", idx, set->latch->page_no);
          } while( idx = set->latch->next );
        }

        set->page_no = bt_getid(bt->mgr->latchmgr->alloc[1].right);

        while( set->page_no ) {
                fprintf(stderr, "free: %.6x\n", (uint)set->page_no);

                if( set->pool = bt_pinpool (bt, set->page_no) )
                        set->page = bt_page (bt, set->pool, set->page_no);
                else
                        return;

            set->page_no = bt_getid(set->page->right);
                bt_unpinpool (set->pool);
        }
#endif
}

typedef struct {
        char type, idx;
        char *infile;
        BtMgr *mgr;
        int num;
} ThreadArg;

//  standalone program to index file of keys
//  then list them onto std-out

#ifdef unix
void *index_file (void *arg)
#else
uint __stdcall index_file (void *arg)
#endif
{
int line = 0, found = 0, cnt = 0;
uid next, page_no = LEAF_page;  // start on first page of leaves
unsigned char key[256];
ThreadArg *args = arg;
int ch, len = 0, slot;
BtPageSet set[1];
time_t tod[1];
BtKey ptr;
BtDb *bt;
FILE *in;

        bt = bt_open (args->mgr);
        time (tod);

        switch(args->type | 0x20)
        {
        case 'a':
                fprintf(stderr, "started latch mgr audit\n");
                bt_latchaudit (bt);
                fprintf(stderr, "finished latch mgr audit\n");
                break;

        case 'w':
                fprintf(stderr, "started indexing for %s\n", args->infile);
                if( in = fopen (args->infile, "rb") )
                  while( ch = getc(in), ch != EOF )
                        if( ch == '\n' )
                        {
                          line++;

                          if( args->num == 1 )
                                sprintf((char *)key+len, "%.9d", 1000000000 - line), len += 9;

                          else if( args->num )
                                sprintf((char *)key+len, "%.9d", line + args->idx * args->num), len += 9;

                          if( bt_insertkey (bt, key, len, line, *tod, 0) )
                                fprintf(stderr, "Error %d Line: %d\n", bt->err, line), exit(0);
                          len = 0;
                        }
                        else if( len < 255 )
                                key[len++] = ch;
                fprintf(stderr, "finished %s for %d keys\n", args->infile, line);
                break;

        case 'd':
                fprintf(stderr, "started deleting keys for %s\n", args->infile);
                if( in = fopen (args->infile, "rb") )
                  while( ch = getc(in), ch != EOF )
                        if( ch == '\n' )
                        {
                          line++;
                          if( args->num == 1 )
                                sprintf((char *)key+len, "%.9d", 1000000000 - line), len += 9;

                          else if( args->num )
                                sprintf((char *)key+len, "%.9d", line + args->idx * args->num), len += 9;

                          if( bt_deletekey (bt, key, len) )
                                fprintf(stderr, "Error %d Line: %d\n", bt->err, line), exit(0);
                          len = 0;
                        }
                        else if( len < 255 )
                                key[len++] = ch;
                fprintf(stderr, "finished %s for keys, %d \n", args->infile, line);
                break;

        case 'f':
                fprintf(stderr, "started finding keys for %s\n", args->infile);
                if( in = fopen (args->infile, "rb") )
                  while( ch = getc(in), ch != EOF )
                        if( ch == '\n' )
                        {
                          line++;
                          if( args->num == 1 )
                                sprintf((char *)key+len, "%.9d", 1000000000 - line), len += 9;

                          else if( args->num )
                                sprintf((char *)key+len, "%.9d", line + args->idx * args->num), len += 9;

                          if( bt_findkey (bt, key, len) )
                                found++;
                          else if( bt->err )
                                fprintf(stderr, "Error %d Syserr %d Line: %d\n", bt->err, errno, line), exit(0);
                          len = 0;
                        }
                        else if( len < 255 )
                                key[len++] = ch;
                fprintf(stderr, "finished %s for %d keys, found %d\n", args->infile, line, found);
                break;

        case 's':
                fprintf(stderr, "started scanning\n");
                do {
                        if( set->pool = bt_pinpool (bt, page_no) )
                                set->page = bt_page (bt, set->pool, page_no);
                        else
                                break;
                        set->latch = bt_pinlatch (bt, page_no);
                        bt_lockpage (BtLockRead, set->latch);
                        next = bt_getid (set->page->right);
                        cnt += set->page->act;

                        for( slot = 0; slot++ < set->page->cnt; )
                         if( next || slot < set->page->cnt )
                          if( !slotptr(set->page, slot)->dead ) {
                                ptr = keyptr(set->page, slot);
                                fwrite (ptr->key, ptr->len, 1, stdout);
                                fputc ('\n', stdout);
                          }

                        bt_unlockpage (BtLockRead, set->latch);
                        bt_unpinlatch (set->latch);
                        bt_unpinpool (set->pool);
                } while( page_no = next );

                cnt--;  // remove stopper key
                fprintf(stderr, " Total keys read %d\n", cnt);
                break;

        case 'c':
                fprintf(stderr, "started counting\n");

                do {
                        if( set->pool = bt_pinpool (bt, page_no) )
                                set->page = bt_page (bt, set->pool, page_no);
                        else
                                break;
                        set->latch = bt_pinlatch (bt, page_no);
                        bt_lockpage (BtLockRead, set->latch);
                        cnt += set->page->act;
                        next = bt_getid (set->page->right);
                        bt_unlockpage (BtLockRead, set->latch);
                        bt_unpinlatch (set->latch);
                        bt_unpinpool (set->pool);
                } while( page_no = next );

                cnt--;  // remove stopper key
                fprintf(stderr, " Total keys read %d\n", cnt);
                break;
        }

        bt_close (bt);
#ifdef unix
        return NULL;
#else
        return 0;
#endif
}

typedef struct timeval timer;

int main (int argc, char **argv)
{
int idx, cnt, len, slot, err;
int segsize, bits = 16;
#ifdef unix
pthread_t *threads;
timer start, stop;
#else
time_t start[1], stop[1];
HANDLE *threads;
#endif
double real_time;
ThreadArg *args;
uint poolsize = 0;
int num = 0;
char key[1];
BtMgr *mgr;
BtKey ptr;
BtDb *bt;

        if( argc < 3 ) {
                fprintf (stderr, "Usage: %s idx_file Read/Write/Scan/Delete/Find [page_bits mapped_segments seg_bits line_numbers src_file1 src_file2 ... ]\n", argv[0]);
                fprintf (stderr, "  where page_bits is the page size in bits\n");
                fprintf (stderr, "  mapped_segments is the number of mmap segments in buffer pool\n");
                fprintf (stderr, "  seg_bits is the size of individual segments in buffer pool in pages in bits\n");
                fprintf (stderr, "  line_numbers = 1 to append line numbers to keys\n");
                fprintf (stderr, "  src_file1 thru src_filen are files of keys separated by newline\n");
                exit(0);
        }

#ifdef unix
        gettimeofday(&start, NULL);
#else
        time(start);
#endif

        if( argc > 3 )
                bits = atoi(argv[3]);

        if( argc > 4 )
                poolsize = atoi(argv[4]);

        if( !poolsize )
                fprintf (stderr, "Warning: no mapped_pool\n");

        if( poolsize > 65535 )
                fprintf (stderr, "Warning: mapped_pool > 65535 segments\n");

        if( argc > 5 )
                segsize = atoi(argv[5]);
        else
                segsize = 4;    // 16 pages per mmap segment

        if( argc > 6 )
                num = atoi(argv[6]);

        cnt = argc - 7;
#ifdef unix
        threads = malloc (cnt * sizeof(pthread_t));
#else
        threads = GlobalAlloc (GMEM_FIXED|GMEM_ZEROINIT, cnt * sizeof(HANDLE));
#endif
        args = malloc (cnt * sizeof(ThreadArg));

        mgr = bt_mgr ((argv[1]), BT_rw, bits, poolsize, segsize, poolsize / 8);

        if( !mgr ) {
                fprintf(stderr, "Index Open Error %s\n", argv[1]);
                exit (1);
        }

        //      fire off threads

        for( idx = 0; idx < cnt; idx++ ) {
                args[idx].infile = argv[idx + 7];
                args[idx].type = argv[2][0];
                args[idx].mgr = mgr;
                args[idx].num = num;
                args[idx].idx = idx;
#ifdef unix
                if( err = pthread_create (threads + idx, NULL, index_file, args + idx) )
                        fprintf(stderr, "Error creating thread %d\n", err);
#else
                threads[idx] = (HANDLE)_beginthreadex(NULL, 65536, index_file, args + idx, 0, NULL);
#endif
        }

        //      wait for termination

#ifdef unix
        for( idx = 0; idx < cnt; idx++ )
                pthread_join (threads[idx], NULL);
        gettimeofday(&stop, NULL);
        real_time = 1000.0 * ( stop.tv_sec - start.tv_sec ) + 0.001 * (stop.tv_usec - start.tv_usec );
#else
        WaitForMultipleObjects (cnt, threads, TRUE, INFINITE);

        for( idx = 0; idx < cnt; idx++ )
                CloseHandle(threads[idx]);

        time (stop);
        real_time = 1000 * (*stop - *start);
#endif
        fprintf(stderr, " Time to complete: %.2f seconds\n", real_time/1000);
        bt_mgrclose (mgr);
}

#endif  //STANDALONE