replace lite weight latch manager

[btree] / btree2u.c

// btree version 2u  sched_yield locks
//      with combined latch & pool manager
//      and phase-fair reader writer lock
// 12 MAR 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 <time.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <errno.h>
#else
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <fcntl.h>
#include <io.h>
#endif

#include <memory.h>
#include <string.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_ro 0x6f72    // ro
#define BT_rw 0x7772    // rw
#define BT_fl 0x6c66    // fl

#define BT_maxbits              15                                      // maximum page size in bits
#define BT_minbits              12                                      // minimum page size in bits
#define BT_minpage              (1 << BT_minbits)       // minimum page size
#define BT_maxpage              (1 << BT_maxbits)       // maximum page size

//  BTree page number constants
#define ALLOC_page              0
#define ROOT_page               1
#define LEAF_page               2
#define LATCH_page              3

//      Number of levels to create in a new BTree

#define MIN_lvl                 2
#define MAX_lvl                 15

/*
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;

//      definition for latch implementation

volatile typedef struct {
        ushort lock[1];
} BtSpinLatch;

#define XCL 1
#define PEND 2
#define BOTH 3
#define SHARE 4

volatile typedef struct {
        ushort rin[1];          // readers in count
        ushort rout[1];         // readers out count
        ushort serving[1];      // writers out count
        ushort ticket[1];       // writers in count
} RWLock;

//      define bits at bottom of rin

#define PHID 0x1        // writer phase (0/1)
#define PRES 0x2        // writer present
#define MASK 0x3        // both write bits
#define RINC 0x4        // reader increment

//      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 2 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
//      cleanup is called. The fence key (highest key) for
//      the page is always present, even if dead.

typedef struct {
#ifdef USETOD
        uint tod;                                       // time-stamp for key
#endif
        ushort off:BT_maxbits;          // page offset for key start
        ushort dead:1;                          // set for deleted 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[0];
} *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:6;           // page size in bits
        unsigned char free:1;           // page is on free list
        unsigned char dirty:1;          // page is dirty in cache
        unsigned char lvl:6;            // level of page
        unsigned char kill:1;           // page is being deleted
        unsigned char clean:1;          // page needs cleaning
        unsigned char right[BtId];      // page number to right
} *BtPage;

typedef struct {
        struct BtPage_ alloc[2];        // next & free page_nos in right ptr
        BtSpinLatch lock[1];            // allocation area lite latch
        volatile uint latchdeployed;// highest number of latch entries deployed
        volatile uint nlatchpage;       // number of latch pages at BT_latch
        volatile uint latchtotal;       // number of page latch entries
        volatile uint latchhash;        // number of latch hash table slots
        volatile uint latchvictim;      // next latch hash entry to examine
        volatile uint safelevel;        // safe page level in cache
        volatile uint cache[MAX_lvl];// cache census counts by btree level
} BtLatchMgr;

//  latch hash table entries

typedef struct {
        volatile uint slot;             // Latch table entry at head of collision chain
        BtSpinLatch latch[1];   // lock for the collision chain
} BtHashEntry;

//      latch manager table structure

typedef struct {
        volatile uid page_no;   // latch set page number on disk
        RWLock readwr[1];               // read/write page lock
        RWLock access[1];               // Access Intent/Page delete
        RWLock parent[1];               // Posting of fence key in parent
        volatile ushort pin;    // number of pins/level/clock bits
        volatile uint next;             // next entry in hash table chain
        volatile uint prev;             // prev entry in hash table chain
} BtLatchSet;

#define CLOCK_mask 0xe000
#define CLOCK_unit 0x2000
#define PIN_mask 0x07ff
#define LVL_mask 0x1800
#define LVL_shift 11

//      The object structure for Btree access

typedef struct _BtDb {
        uint page_size;         // each page size       
        uint page_bits;         // each page size in bits       
        uid page_no;            // current page number  
        uid cursor_page;        // current cursor page number   
        int  err;
        uint mode;                      // read-write mode
        BtPage cursor;          // cached frame for start/next (never mapped)
        BtPage frame;           // spare frame for the page split (never mapped)
        BtPage page;            // current mapped page in buffer pool
        BtLatchSet *latch;                      // current page latch
        BtLatchMgr *latchmgr;           // mapped latch page from allocation page
        BtLatchSet *latchsets;          // mapped latch set from latch pages
        unsigned char *pagepool;        // cached page pool set
        BtHashEntry *table;     // the hash table
#ifdef unix
        int idx;
#else
        HANDLE idx;
        HANDLE halloc;          // allocation and latch table handle
#endif
        unsigned char *mem;     // frame, cursor, memory buffers
        uint found;                     // last deletekey found key
} BtDb;

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

// B-Tree functions
extern void bt_close (BtDb *bt);
extern BtDb *bt_open (char *name, uint mode, uint bits, uint cacheblk);
extern BTERR  bt_insertkey (BtDb *bt, unsigned char *key, uint len, uint lvl, uid id, uint tod);
extern BTERR  bt_deletekey (BtDb *bt, unsigned char *key, uint len, uint lvl);
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
void bt_update (BtDb *bt, BtPage page);
BtPage bt_mappage (BtDb *bt, BtLatchSet *latch);
//  Helper functions to return slot values

extern BtKey bt_key (BtDb *bt, uint slot);
extern uid bt_uid (BtDb *bt, uint slot);
#ifdef USETOD
extern uint bt_tod (BtDb *bt, uint slot);
#endif

//  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 right
//      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 always
//      present, even after deletion and cleanup.

//  Deleted leaf pages are reclaimed  on a free list.
//      The upper levels of the btree are fixed on creation.

//  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 (ALLOC page) is dedicated to lock for new page extensions,
//      and chains empty leaf pages together for reuse.

//      Parent locks are obtained to prevent resplitting or deleting a node
//      before its fence is posted into its upper level.

//      A special open mode of BT_fl is provided to safely access files on
//      WIN32 networks. WIN32 network operations should not use memory mapping.
//      This WIN32 mode sets FILE_FLAG_NOBUFFERING and FILE_FLAG_WRITETHROUGH
//      to prevent local caching of network file contents.

//      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;
}

BTERR bt_abort (BtDb *bt, BtPage page, uid page_no, BTERR err)
{
BtKey ptr;

        fprintf(stderr, "\n Btree2 abort, error %d on page %.8x\n", err, page_no);
        fprintf(stderr, "level=%d kill=%d free=%d cnt=%x act=%x\n", page->lvl, page->kill, page->free, page->cnt, page->act);
        ptr = keyptr(page, page->cnt);
        fprintf(stderr, "fence='%.*s'\n", ptr->len, ptr->key);
        fprintf(stderr, "right=%.8x\n", bt_getid(page->right));
        return bt->err = err;
}

//      Phase-Fair reader/writer lock implementation

void WriteLock (RWLock *lock)
{
ushort w, r, tix;

#ifdef unix
        tix = __sync_fetch_and_add (lock->ticket, 1);
#else
        tix = _InterlockedExchangeAdd16 (lock->ticket, 1);
#endif
        // wait for our ticket to come up

        while( tix != lock->serving[0] )
#ifdef unix
                sched_yield();
#else
                SwitchToThread ();
#endif

        w = PRES | (tix & PHID);
#ifdef  unix
        r = __sync_fetch_and_add (lock->rin, w);
#else
        r = _InterlockedExchangeAdd16 (lock->rin, w);
#endif
        while( r != *lock->rout )
#ifdef unix
                sched_yield();
#else
                SwitchToThread();
#endif
}

void WriteRelease (RWLock *lock)
{
#ifdef unix
        __sync_fetch_and_and (lock->rin, ~MASK);
#else
        _InterlockedAnd16 (lock->rin, ~MASK);
#endif
        lock->serving[0]++;
}

void ReadLock (RWLock *lock)
{
ushort w;
#ifdef unix
        w = __sync_fetch_and_add (lock->rin, RINC) & MASK;
#else
        w = _InterlockedExchangeAdd16 (lock->rin, RINC) & MASK;
#endif
        if( w )
          while( w == (*lock->rin & MASK) )
#ifdef unix
                sched_yield ();
#else
                SwitchToThread ();
#endif
}

void ReadRelease (RWLock *lock)
{
#ifdef unix
        __sync_fetch_and_add (lock->rout, RINC);
#else
        _InterlockedExchangeAdd16 (lock->rout, RINC);
#endif
}

//      Spin Latch Manager

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

void bt_spinreadlock(BtSpinLatch *latch)
{
ushort prev;

  do {
#ifdef unix
        prev = __sync_fetch_and_add (latch->lock, SHARE);
#else
        prev = _InterlockedExchangeAdd16(latch->lock, SHARE);
#endif
        //  see if exclusive request is granted or pending

        if( !(prev & BOTH) )
                return;
#ifdef unix
        prev = __sync_fetch_and_add (latch->lock, -SHARE);
#else
        prev = _InterlockedExchangeAdd16(latch->lock, -SHARE);
#endif
#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)
{
ushort prev;

  do {
#ifdef  unix
        prev = __sync_fetch_and_or(latch->lock, PEND | XCL);
#else
        prev = _InterlockedOr16(latch->lock, PEND | XCL);
#endif
        if( !(prev & XCL) )
          if( !(prev & ~BOTH) )
                return;
          else
#ifdef unix
                __sync_fetch_and_and (latch->lock, ~XCL);
#else
                _InterlockedAnd16(latch->lock, ~XCL);
#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
        prev = __sync_fetch_and_or(latch->lock, XCL);
#else
        prev = _InterlockedOr16(latch->lock, XCL);
#endif
        //      take write access if all bits are clear

        if( !(prev & XCL) )
          if( !(prev & ~BOTH) )
                return 1;
          else
#ifdef unix
                __sync_fetch_and_and (latch->lock, ~XCL);
#else
                _InterlockedAnd16(latch->lock, ~XCL);
#endif
        return 0;
}

//      clear write mode

void bt_spinreleasewrite(BtSpinLatch *latch)
{
#ifdef unix
        __sync_fetch_and_and(latch->lock, ~BOTH);
#else
        _InterlockedAnd16(latch->lock, ~BOTH);
#endif
}

//      decrement reader count

void bt_spinreleaseread(BtSpinLatch *latch)
{
#ifdef unix
        __sync_fetch_and_add(latch->lock, -SHARE);
#else
        _InterlockedExchangeAdd16(latch->lock, -SHARE);
#endif
}

//      read page from permanent location in Btree file

BTERR bt_readpage (BtDb *bt, BtPage page, uid page_no)
{
off64_t off = page_no << bt->page_bits;

#ifdef unix
        if( pread (bt->idx, page, bt->page_size, page_no << bt->page_bits) < bt->page_size ) {
                fprintf (stderr, "Unable to read page %.8x errno = %d\n", page_no, errno);
                return bt->err = BTERR_read;
        }
#else
OVERLAPPED ovl[1];
uint amt[1];

        memset (ovl, 0, sizeof(OVERLAPPED));
        ovl->Offset = off;
        ovl->OffsetHigh = off >> 32;

        if( !ReadFile(bt->idx, page, bt->page_size, amt, ovl)) {
                fprintf (stderr, "Unable to read page %.8x GetLastError = %d\n", page_no, GetLastError());
                return bt->err = BTERR_read;
        }
        if( *amt <  bt->page_size ) {
                fprintf (stderr, "Unable to read page %.8x GetLastError = %d\n", page_no, GetLastError());
                return bt->err = BTERR_read;
        }
#endif
        return 0;
}

//      write page to permanent location in Btree file
//      clear the dirty bit

BTERR bt_writepage (BtDb *bt, BtPage page, uid page_no)
{
off64_t off = page_no << bt->page_bits;

#ifdef unix
        page->dirty = 0;

        if( pwrite(bt->idx, page, bt->page_size, off) < bt->page_size )
                return bt->err = BTERR_wrt;
#else
OVERLAPPED ovl[1];
uint amt[1];

        memset (ovl, 0, sizeof(OVERLAPPED));
        ovl->Offset = off;
        ovl->OffsetHigh = off >> 32;
        page->dirty = 0;

        if( !WriteFile(bt->idx, page, bt->page_size, amt, ovl) )
                return bt->err = BTERR_wrt;

        if( *amt <  bt->page_size )
                return bt->err = BTERR_wrt;
#endif
        return 0;
}

//      link latch table entry into head of latch hash table

BTERR bt_latchlink (BtDb *bt, uint hashidx, uint slot, uid page_no)
{
BtPage page = (BtPage)((uid)slot * bt->page_size + bt->pagepool);
BtLatchSet *latch = bt->latchsets + slot;
int lvl;

        if( latch->next = bt->table[hashidx].slot )
                bt->latchsets[latch->next].prev = slot;

        bt->table[hashidx].slot = slot;
        latch->page_no = page_no;
        latch->prev = 0;
        latch->pin = 1;

        if( bt_readpage (bt, page, page_no) )
                return bt->err;

        lvl = page->lvl << LVL_shift;
        if( lvl > LVL_mask )
                lvl = LVL_mask;
        latch->pin |= lvl;              // store lvl
        latch->pin |= lvl << 3; // initialize clock

#ifdef unix
        __sync_fetch_and_add (&bt->latchmgr->cache[page->lvl], 1);
#else
        _InterlockedAdd(&bt->latchmgr->cache[page->lvl], 1);
#endif
        return bt->err = 0;
}

//      release latch pin

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

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

BtLatchSet *bt_pinlatch (BtDb *bt, uid page_no)
{
uint hashidx = page_no % bt->latchmgr->latchhash;
BtLatchSet *latch;
uint slot, idx;
uint lvl, cnt;
off64_t off;
uint amt[1];
BtPage page;

  //  try to find our entry

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

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

  //  found our entry
  //  increment clock

  if( slot ) {
        latch = bt->latchsets + slot;
        lvl = (latch->pin & LVL_mask) >> LVL_shift;
        lvl *= CLOCK_unit * 2;
        lvl |= CLOCK_unit;
#ifdef unix
        __sync_fetch_and_add(&latch->pin, 1);
        __sync_fetch_and_or(&latch->pin, lvl);
#else
        _InterlockedIncrement16 (&latch->pin);
        _InterlockedOr16 (&latch->pin, lvl);
#endif
        bt_spinreleasewrite(bt->table[hashidx].latch);
        return latch;
  }

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

        if( slot < bt->latchmgr->latchtotal ) {
                latch = bt->latchsets + slot;
                if( bt_latchlink (bt, hashidx, slot, page_no) )
                        return NULL;
                bt_spinreleasewrite (bt->table[hashidx].latch);
                return latch;
        }

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

  while( 1 ) {
#ifdef unix
        slot = __sync_fetch_and_add(&bt->latchmgr->latchvictim, 1);
#else
        slot = _InterlockedIncrement (&bt->latchmgr->latchvictim) - 1;
#endif
        // try to get write lock on hash chain
        //      skip entry if not obtained
        //      or has outstanding pins

        slot %= bt->latchmgr->latchtotal;

        //      on slot wraparound, check census
        //      count and increment safe level

        cnt = bt->latchmgr->cache[bt->latchmgr->safelevel];

        if( !slot ) {
          if( cnt < bt->latchmgr->latchtotal / 10 )
#ifdef unix
                __sync_fetch_and_add(&bt->latchmgr->safelevel, 1);
#else
                _InterlockedIncrement (&bt->latchmgr->safelevel);
#endif
          continue;
        }

        latch = bt->latchsets + slot;
        idx = latch->page_no % bt->latchmgr->latchhash;
        lvl = (latch->pin & LVL_mask) >> LVL_shift;

        //      see if we are evicting this level yet
        //      or if we are on same chain as hashidx

        if( idx == hashidx || lvl > bt->latchmgr->safelevel )
                continue;

        if( !bt_spinwritetry (bt->table[idx].latch) )
                continue;

        if( latch->pin & ~LVL_mask ) {
          if( latch->pin & CLOCK_mask )
#ifdef unix
                __sync_fetch_and_add(&latch->pin, -CLOCK_unit);
#else
                _InterlockedExchangeAdd16 (&latch->pin, -CLOCK_unit);
#endif
          bt_spinreleasewrite (bt->table[idx].latch);
          continue;
        }

        //  update permanent page area in btree

        page = (BtPage)((uid)slot * bt->page_size + bt->pagepool);
#ifdef unix
        posix_fadvise (bt->idx, page_no << bt->page_bits, bt->page_size, POSIX_FADV_WILLNEED);
        __sync_fetch_and_add (&bt->latchmgr->cache[page->lvl], -1);
#else
        _InterlockedAdd(&bt->latchmgr->cache[page->lvl], -1);
#endif
        if( page->dirty )
          if( bt_writepage (bt, page, latch->page_no) )
                return NULL;

        //  unlink our available slot from its hash chain

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

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

        bt_spinreleasewrite (bt->table[idx].latch);

        if( bt_latchlink (bt, hashidx, slot, page_no) )
                return NULL;

        bt_spinreleasewrite (bt->table[hashidx].latch);
        return latch;
  }
}

//      close and release memory

void bt_close (BtDb *bt)
{
#ifdef unix
        munmap (bt->table, bt->latchmgr->nlatchpage * bt->page_size);
        munmap (bt->latchmgr, bt->page_size);
#else
        FlushViewOfFile(bt->latchmgr, 0);
        UnmapViewOfFile(bt->latchmgr);
        CloseHandle(bt->halloc);
#endif
#ifdef unix
        if( bt->mem )
                free (bt->mem);
        close (bt->idx);
        free (bt);
#else
        if( bt->mem)
                VirtualFree (bt->mem, 0, MEM_RELEASE);
        FlushFileBuffers(bt->idx);
        CloseHandle(bt->idx);
        GlobalFree (bt);
#endif
}
//  open/create new btree

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

BtDb *bt_open (char *name, uint mode, uint bits, uint nodemax)
{
uint lvl, attr, last, slot, idx;
uint nlatchpage, latchhash;
BtLatchMgr *latchmgr;
off64_t size, off;
uint amt[1];
BtKey key;
BtDb* bt;
int flag;

#ifndef unix
OVERLAPPED ovl[1];
#else
struct flock lock[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( mode == BT_ro ) {
                fprintf(stderr, "ReadOnly mode not supported: %s\n", name);
                return NULL;
        }
#ifdef unix
        bt = calloc (1, sizeof(BtDb));

        bt->idx = open ((char*)name, O_RDWR | O_CREAT, 0666);
        posix_fadvise( bt->idx, 0, 0, POSIX_FADV_RANDOM);
 
        if( bt->idx == -1 ) {
                fprintf(stderr, "unable to open %s\n", name);
                return free(bt), NULL;
        }
#else
        bt = GlobalAlloc (GMEM_FIXED|GMEM_ZEROINIT, sizeof(BtDb));
        attr = FILE_ATTRIBUTE_NORMAL;
        bt->idx = CreateFile(name, GENERIC_READ| GENERIC_WRITE, FILE_SHARE_READ|FILE_SHARE_WRITE, NULL, OPEN_ALWAYS, attr, NULL);

        if( bt->idx == INVALID_HANDLE_VALUE ) {
                fprintf(stderr, "unable to open %s\n", name);
                return GlobalFree(bt), NULL;
        }
#endif
#ifdef unix
        memset (lock, 0, sizeof(lock));
        lock->l_len = sizeof(struct BtPage_);
        lock->l_type = F_WRLCK;

        if( fcntl (bt->idx, F_SETLKW, lock) < 0 ) {
                fprintf(stderr, "unable to lock record zero %s\n", name);
                return bt_close (bt), NULL;
        }
#else
        memset (ovl, 0, sizeof(ovl));

        //      use large offsets to
        //      simulate advisory locking

        ovl->OffsetHigh |= 0x80000000;

        if( !LockFileEx (bt->idx, LOCKFILE_EXCLUSIVE_LOCK, 0, sizeof(struct BtPage_), 0L, ovl) ) {
                fprintf(stderr, "unable to lock record zero %s, GetLastError = %d\n", name, GetLastError());
                return bt_close (bt), NULL;
        }
#endif 

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

        // read minimum page size to get root info

        if( size = lseek (bt->idx, 0L, 2) ) {
                if( pread(bt->idx, latchmgr, BT_minpage, 0) == BT_minpage )
                        bits = latchmgr->alloc->bits;
                else {
                        fprintf(stderr, "Unable to read page zero\n");
                        return free(bt), free(latchmgr), NULL;
                }
        }
#else
        latchmgr = VirtualAlloc(NULL, BT_maxpage, MEM_COMMIT, PAGE_READWRITE);
        size = GetFileSize(bt->idx, amt);

        if( size || *amt ) {
                if( !ReadFile(bt->idx, (char *)latchmgr, BT_minpage, amt, NULL) ) {
                        fprintf(stderr, "Unable to read page zero\n");
                        return bt_close (bt), NULL;
                } else
                        bits = latchmgr->alloc->bits;
        }
#endif

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

        bt->mode = mode;

        if( size || *amt ) {
                nlatchpage = latchmgr->nlatchpage;
                goto btlatch;
        }

        if( nodemax < 16 ) {
                fprintf(stderr, "Buffer pool too small: %d\n", nodemax);
                return bt_close(bt), NULL;
        }

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

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

        //  calculate number of latch hash table entries

        nlatchpage = (nodemax/16 * sizeof(BtHashEntry) + bt->page_size - 1) / bt->page_size;
        latchhash = nlatchpage * bt->page_size / sizeof(BtHashEntry);

        nlatchpage += nodemax;          // size of the buffer pool in pages
        nlatchpage += (sizeof(BtLatchSet) * nodemax + bt->page_size - 1)/bt->page_size;

        bt_putid(latchmgr->alloc->right, MIN_lvl+1+nlatchpage);
        latchmgr->nlatchpage = nlatchpage;
        latchmgr->latchtotal = nodemax;
        latchmgr->latchhash = latchhash;

        if( bt_writepage (bt, latchmgr->alloc, 0) ) {
                fprintf (stderr, "Unable to create btree page zero\n");
                return bt_close (bt), NULL;
        }

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

        for( lvl=MIN_lvl; lvl--; ) {
                last = MIN_lvl - lvl;   // page number
                slotptr(latchmgr->alloc, 1)->off = bt->page_size - 3;
                bt_putid(slotptr(latchmgr->alloc, 1)->id, lvl ? last + 1 : 0);
                key = keyptr(latchmgr->alloc, 1);
                key->len = 2;           // create stopper key
                key->key[0] = 0xff;
                key->key[1] = 0xff;

                latchmgr->alloc->min = bt->page_size - 3;
                latchmgr->alloc->lvl = lvl;
                latchmgr->alloc->cnt = 1;
                latchmgr->alloc->act = 1;

                if( bt_writepage (bt, latchmgr->alloc, last) ) {
                        fprintf (stderr, "Unable to create btree page %.8x\n", last);
                        return bt_close (bt), NULL;
                }
        }

        // clear out buffer pool pages

        memset(latchmgr, 0, bt->page_size);
        last = MIN_lvl + nlatchpage;

        if( bt_writepage (bt, latchmgr->alloc, last) ) {
                fprintf (stderr, "Unable to write buffer pool page %.8x\n", last);
                return bt_close (bt), NULL;
        }
                
#ifdef unix
        free (latchmgr);
#else
        VirtualFree (latchmgr, 0, MEM_RELEASE);
#endif

btlatch:
#ifdef unix
        lock->l_type = F_UNLCK;
        if( fcntl (bt->idx, F_SETLK, lock) < 0 ) {
                fprintf (stderr, "Unable to unlock page zero\n");
                return bt_close (bt), NULL;
        }
#else
        if( !UnlockFileEx (bt->idx, 0, sizeof(struct BtPage_), 0, ovl) ) {
                fprintf (stderr, "Unable to unlock page zero, GetLastError = %d\n", GetLastError());
                return bt_close (bt), NULL;
        }
#endif
#ifdef unix
        flag = PROT_READ | PROT_WRITE;
        bt->latchmgr = mmap (0, bt->page_size, flag, MAP_SHARED, bt->idx, ALLOC_page * bt->page_size);
        if( bt->latchmgr == MAP_FAILED ) {
                fprintf (stderr, "Unable to mmap page zero, errno = %d", errno);
                return bt_close (bt), NULL;
        }
        bt->table = (void *)mmap (0, (uid)nlatchpage * bt->page_size, flag, MAP_SHARED, bt->idx, LATCH_page * bt->page_size);
        if( bt->table == MAP_FAILED ) {
                fprintf (stderr, "Unable to mmap buffer pool, errno = %d", errno);
                return bt_close (bt), NULL;
        }
        madvise (bt->table, (uid)nlatchpage << bt->page_bits, MADV_RANDOM | MADV_WILLNEED);
#else
        flag = PAGE_READWRITE;
        bt->halloc = CreateFileMapping(bt->idx, NULL, flag, 0, ((uid)nlatchpage + LATCH_page) * bt->page_size, NULL);
        if( !bt->halloc ) {
                fprintf (stderr, "Unable to create file mapping for buffer pool mgr, GetLastError = %d\n", GetLastError());
                return bt_close (bt), NULL;
        }

        flag = FILE_MAP_WRITE;
        bt->latchmgr = MapViewOfFile(bt->halloc, flag, 0, 0, ((uid)nlatchpage + LATCH_page) * bt->page_size);
        if( !bt->latchmgr ) {
                fprintf (stderr, "Unable to map buffer pool, GetLastError = %d\n", GetLastError());
                return bt_close (bt), NULL;
        }

        bt->table = (void *)((char *)bt->latchmgr + LATCH_page * bt->page_size);
#endif
        bt->pagepool = (unsigned char *)bt->table + (uid)(nlatchpage - bt->latchmgr->latchtotal) * bt->page_size;
        bt->latchsets = (BtLatchSet *)(bt->pagepool - (uid)bt->latchmgr->latchtotal * sizeof(BtLatchSet));

#ifdef unix
        bt->mem = valloc (2 * bt->page_size);
#else
        bt->mem = VirtualAlloc(NULL, 2 * bt->page_size, MEM_COMMIT, PAGE_READWRITE);
#endif
        bt->frame = (BtPage)bt->mem;
        bt->cursor = (BtPage)(bt->mem + bt->page_size);
        return bt;
}

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

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

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

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

//      allocate a new page and write page into it

uid bt_newpage(BtDb *bt, BtPage page)
{
BtLatchSet *latch;
uid new_page;
BtPage temp;

        //      lock allocation page

        bt_spinwritelock(bt->latchmgr->lock);

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

        if( new_page = bt_getid(bt->latchmgr->alloc[1].right) ) {
          if( latch = bt_pinlatch (bt, new_page) )
                temp = bt_mappage (bt, latch);
          else
                return 0;

          bt_putid(bt->latchmgr->alloc[1].right, bt_getid(temp->right));
          bt_spinreleasewrite(bt->latchmgr->lock);
          memcpy (temp, page, bt->page_size);

          bt_update (bt, temp);
          bt_unpinlatch (latch);
          return new_page;
        } else {
          new_page = bt_getid(bt->latchmgr->alloc->right);
          bt_putid(bt->latchmgr->alloc->right, new_page+1);
          bt_spinreleasewrite(bt->latchmgr->lock);

          if( bt_writepage (bt, page, new_page) )
                return 0;
        }

        bt_update (bt, bt->latchmgr->alloc);
        return new_page;
}

//  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;
}

//  Update current page of btree by
//      flushing mapped area to disk backing of cache pool.
//      mark page as dirty for rewrite to permanent location

void bt_update (BtDb *bt, BtPage page)
{
#ifdef unix
        msync (page, bt->page_size, MS_ASYNC);
#else
//      FlushViewOfFile (page, bt->page_size);
#endif
        page->dirty = 1;
}

//  map the btree cached page onto current page

BtPage bt_mappage (BtDb *bt, BtLatchSet *latch)
{
        return (BtPage)((uid)(latch - bt->latchsets) * bt->page_size + bt->pagepool);
}

//      deallocate a deleted page 
//      place on free chain out of allocator page
//      call with page latched for Writing and Deleting

BTERR bt_freepage(BtDb *bt, uid page_no, BtLatchSet *latch)
{
BtPage page = bt_mappage (bt, latch);

        //      lock allocation page

        bt_spinwritelock (bt->latchmgr->lock);

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

        page->free = 1;
        bt_update(bt, page);

        // unlock released page

        bt_unlockpage (BtLockDelete, latch);
        bt_unlockpage (BtLockWrite, latch);
        bt_unpinlatch (latch);

        // unlock allocation page

        bt_spinreleasewrite (bt->latchmgr->lock);
        bt_update (bt, bt->latchmgr->alloc);
        return 0;
}

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

int bt_findslot (BtDb *bt, unsigned char *key, uint len)
{
uint diff, higher = bt->page->cnt, low = 1, slot;
uint good = 0;

        //      make stopper key an infinite fence value

        if( bt_getid (bt->page->right) )
                higher++;
        else
                good++;

        //      low is the lowest candidate, higher is already
        //      tested as .ge. the given key, loop ends when they meet

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

        //      return zero if key is on right link page

        return good ? higher : 0;
}

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

int bt_loadpage (BtDb *bt, 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;

  //  start at root of btree and drill down

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

        if( bt->latch = bt_pinlatch(bt, page_no) )
                bt->page_no = page_no;
        else
                return 0;

        // obtain access lock using lock chaining

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

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

        // obtain read lock using lock chaining

        bt_lockpage(mode, bt->latch);

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

        //      map/obtain page contents

        bt->page = bt_mappage (bt, bt->latch);

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

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

                if( lock != BtLockRead && drill == lvl ) {
                        bt_unlockpage(mode, bt->latch);
                        bt_unpinlatch(bt->latch);
                        continue;
                }
        }

        prevpage = bt->page_no;
        prevlatch = bt->latch;
        prevmode = mode;

        //  find key on page at this level
        //  and descend to requested level

        if( !bt->page->kill )
         if( slot = bt_findslot (bt, key, len) ) {
          if( drill == lvl )
                return slot;

          while( slotptr(bt->page, slot)->dead )
                if( slot++ < bt->page->cnt )
                        continue;
                else
                        goto slideright;

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

        //  or slide right into next page

slideright:
        page_no = bt_getid(bt->page->right);

  } while( page_no );

  // return error on end of right chain

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

//      a fence key was deleted from a page
//      push new fence value upwards

BTERR bt_fixfence (BtDb *bt, uid page_no, uint lvl)
{
unsigned char leftkey[256], rightkey[256];
BtLatchSet *latch = bt->latch;
BtKey ptr;

        // remove deleted key, the old fence value

        ptr = keyptr(bt->page, bt->page->cnt);
        memcpy(rightkey, ptr, ptr->len + 1);

        memset (slotptr(bt->page, bt->page->cnt--), 0, sizeof(BtSlot));
        bt->page->clean = 1;

        ptr = keyptr(bt->page, bt->page->cnt);
        memcpy(leftkey, ptr, ptr->len + 1);

        bt_update (bt, bt->page);
        bt_lockpage (BtLockParent, latch);
        bt_unlockpage (BtLockWrite, latch);

        //  insert new (now smaller) fence key

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

        //  remove old (larger) fence key

        if( bt_deletekey (bt, rightkey+1, *rightkey, lvl + 1) )
                return bt->err;

        bt_unlockpage (BtLockParent, latch);
        bt_unpinlatch (latch);
        return 0;
}

//      root has a single child
//      collapse a level from the btree
//      call with root locked in bt->page

BTERR bt_collapseroot (BtDb *bt, BtPage root)
{
BtLatchSet *latch;
BtPage temp;
uid child;
uint idx;

        // find the child entry
        //      and promote to new root

  do {
        for( idx = 0; idx++ < root->cnt; )
          if( !slotptr(root, idx)->dead )
                break;

        child = bt_getid (slotptr(root, idx)->id);
        if( latch = bt_pinlatch (bt, child) )
                temp = bt_mappage (bt, latch);
        else
                return bt->err;

        bt_lockpage (BtLockDelete, latch);
        bt_lockpage (BtLockWrite, latch);
        memcpy (root, temp, bt->page_size);

        bt_update (bt, root);

        if( bt_freepage (bt, child, latch) )
                return bt->err;

  } while( root->lvl > 1 && root->act == 1 );

  bt_unlockpage (BtLockWrite, bt->latch);
  bt_unpinlatch (bt->latch);
  return 0;
}

//  find and delete key on page by marking delete flag bit
//  when page becomes empty, delete it

BTERR bt_deletekey (BtDb *bt, unsigned char *key, uint len, uint lvl)
{
unsigned char lowerkey[256], higherkey[256];
uint slot, dirty = 0, idx, fence, found;
BtLatchSet *latch, *rlatch;
uid page_no, right;
BtPage temp;
BtKey ptr;

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

        // are we deleting a fence slot?

        fence = slot == bt->page->cnt;

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

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

                // collapse empty slots

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

        right = bt_getid(bt->page->right);
        page_no = bt->page_no;
        latch = bt->latch;

        if( !dirty ) {
          if( lvl )
                return bt_abort (bt, bt->page, page_no, BTERR_notfound);
          bt_unlockpage(BtLockWrite, latch);
          bt_unpinlatch (latch);
          return bt->found = found, 0;
        }

        //      did we delete a fence key in an upper level?

        if( lvl && bt->page->act && fence )
          if( bt_fixfence (bt, page_no, lvl) )
                return bt->err;
          else
                return bt->found = found, 0;

        //      is this a collapsed root?

        if( lvl > 1 && page_no == ROOT_page && bt->page->act == 1 )
          if( bt_collapseroot (bt, bt->page) )
                return bt->err;
          else
                return bt->found = found, 0;

        // return if page is not empty

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

        // cache copy of fence key
        //      in order to find parent

        ptr = keyptr(bt->page, bt->page->cnt);
        memcpy(lowerkey, ptr, ptr->len + 1);

        // obtain lock on right page

        if( rlatch = bt_pinlatch (bt, right) )
                temp = bt_mappage (bt, rlatch);
        else
                return bt->err;

        bt_lockpage(BtLockWrite, rlatch);

        if( temp->kill ) {
                bt_abort(bt, temp, right, 0);
                return bt_abort(bt, bt->page, bt->page_no, BTERR_kill);
        }

        // pull contents of next page into current empty page 

        memcpy (bt->page, temp, bt->page_size);

        //      cache copy of key to update

        ptr = keyptr(temp, temp->cnt);
        memcpy(higherkey, ptr, ptr->len + 1);

        //  Mark right page as deleted and point it to left page
        //      until we can post updates at higher level.

        bt_putid(temp->right, page_no);
        temp->kill = 1;

        bt_update(bt, bt->page);
        bt_update(bt, temp);

        bt_lockpage(BtLockParent, latch);
        bt_unlockpage(BtLockWrite, latch);

        bt_lockpage(BtLockParent, rlatch);
        bt_unlockpage(BtLockWrite, rlatch);

        //  redirect higher key directly to consolidated node

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

        //  delete old lower key to consolidated node

        if( bt_deletekey (bt, lowerkey + 1, *lowerkey, lvl + 1) )
                return bt->err;

        //  obtain write & delete lock on deleted node
        //      add right block to free chain

        bt_lockpage(BtLockDelete, rlatch);
        bt_lockpage(BtLockWrite, rlatch);
        bt_unlockpage(BtLockParent, rlatch);

        if( bt_freepage (bt, right, rlatch) )
                return bt->err;

        bt_unlockpage(BtLockParent, latch);
        bt_unpinlatch(latch);
        return 0;
}

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

uid bt_findkey (BtDb *bt, unsigned char *key, uint len)
{
uint  slot;
BtKey ptr;
uid id;

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

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

        if( ptr->len == len && !memcmp (ptr->key, key, len) )
                id = bt_getid(slotptr(bt->page,slot)->id);
        else
                id = 0;

        bt_unlockpage (BtLockRead, bt->latch);
        bt_unpinlatch (bt->latch);
        return id;
}

//      check page for space available,
//      clean if necessary and return
//      0 - page needs splitting
//      >0 - go ahead with new slot
 
uint bt_cleanpage(BtDb *bt, uint amt, uint slot)
{
uint nxt = bt->page_size;
BtPage page = bt->page;
uint cnt = 0, idx = 0;
uint max = page->cnt;
uint newslot = slot;
BtKey key;
int ret;

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

        //      skip cleanup if nothing to reclaim

        if( !page->clean )
                return 0;

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

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

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

        while( cnt++ < max ) {
                if( cnt == slot )
                        newslot = idx + 1;
                // always leave fence key in list
                if( cnt < max && slotptr(bt->frame,cnt)->dead )
                        continue;

                // copy key
                key = keyptr(bt->frame, cnt);
                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);
                if( !(slotptr(page, idx)->dead = slotptr(bt->frame, cnt)->dead) )
                        page->act++;
#ifdef USETOD
                slotptr(page, idx)->tod = slotptr(bt->frame, cnt)->tod;
#endif
                slotptr(page, idx)->off = nxt;
        }

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

        if( page->min >= (max+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, unsigned char *leftkey, uid page_no2)
{
uint nxt = bt->page_size;
BtPage root = bt->page;
uid right;

        //  Obtain an empty page to use, and copy the current
        //  root contents into it

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

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

        memset(root+1, 0, bt->page_size - sizeof(*root));

        // insert first key on newroot page

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

        nxt -= 3;
        ((unsigned char *)root)[nxt] = 2;
        ((unsigned char *)root)[nxt+1] = 0xff;
        ((unsigned char *)root)[nxt+2] = 0xff;
        bt_putid(slotptr(root, 2)->id, page_no2);
        slotptr(root, 2)->off = nxt;

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

        // update and release root (bt->page)

        bt_update(bt, root);

        bt_unlockpage(BtLockWrite, bt->latch);
        bt_unpinlatch(bt->latch);
        return 0;
}

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

BTERR bt_splitpage (BtDb *bt)
{
uint cnt = 0, idx = 0, max, nxt = bt->page_size;
unsigned char fencekey[256], rightkey[256];
uid page_no = bt->page_no, right;
BtLatchSet *latch, *rlatch;
BtPage page = bt->page;
uint lvl = page->lvl;
BtKey key;

        latch = bt->latch;

        //  split higher half of keys to bt->frame
        //      the last key (fence key) might be dead

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

        while( cnt++ < max ) {
                key = keyptr(page, cnt);
                nxt -= key->len + 1;
                memcpy ((unsigned char *)bt->frame + nxt, key, key->len + 1);
                memcpy(slotptr(bt->frame,++idx)->id, slotptr(page,cnt)->id, BtId);
                if( !(slotptr(bt->frame, idx)->dead = slotptr(page, cnt)->dead) )
                        bt->frame->act++;
#ifdef USETOD
                slotptr(bt->frame, idx)->tod = slotptr(page, cnt)->tod;
#endif
                slotptr(bt->frame, idx)->off = nxt;
        }

        //      remember fence key for new right page

        memcpy (rightkey, key, key->len + 1);

        bt->frame->bits = bt->page_bits;
        bt->frame->min = nxt;
        bt->frame->cnt = idx;
        bt->frame->lvl = lvl;

        // link right node

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

        //      get new free page and write frame to it.

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

        //      update lower keys to continue in old page

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

        //  assemble page of smaller keys
        //      (they're all active keys)

        while( cnt++ < max / 2 ) {
                key = keyptr(bt->frame, cnt);
                nxt -= key->len + 1;
                memcpy ((unsigned char *)page + nxt, key, key->len + 1);
                memcpy(slotptr(page,++idx)->id, slotptr(bt->frame,cnt)->id, BtId);
#ifdef USETOD
                slotptr(page, idx)->tod = slotptr(bt->frame, cnt)->tod;
#endif
                slotptr(page, idx)->off = nxt;
                page->act++;
        }

        // remember fence key for smaller page

        memcpy (fencekey, key, key->len + 1);

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

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

        if( page_no == ROOT_page )
                return bt_splitroot (bt, fencekey, right);

        //      lock right page

        if( rlatch = bt_pinlatch (bt, right) )
                bt_lockpage (BtLockParent, rlatch);
        else
                return bt->err;

        // update left (containing) node

        bt_update(bt, page);

        bt_lockpage (BtLockParent, latch);
        bt_unlockpage (BtLockWrite, latch);

        // insert new fence for reformulated left block

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

        //      switch fence for right block of larger keys to new right page

        if( bt_insertkey (bt, rightkey+1, *rightkey, lvl+1, right, time(NULL)) )
                return bt->err;

        bt_unlockpage (BtLockParent, latch);
        bt_unlockpage (BtLockParent, rlatch);

        bt_unpinlatch (rlatch);
        bt_unpinlatch (latch);
        return 0;
}

//  Insert new key into the btree at requested level.
//  Pages are unlocked at exit.

BTERR bt_insertkey (BtDb *bt, unsigned char *key, uint len, uint lvl, uid id, uint tod)
{
uint slot, idx;
BtPage page;
BtKey ptr;

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

        // if key already exists, update id and return

        page = bt->page;

        if( !keycmp (ptr, key, len) ) {
          if( slotptr(page, slot)->dead )
                page->act++;
          slotptr(page, slot)->dead = 0;
#ifdef USETOD
          slotptr(page, slot)->tod = tod;
#endif
          bt_putid(slotptr(page,slot)->id, id);
          bt_update(bt, bt->page);
          bt_unlockpage(BtLockWrite, bt->latch);
          bt_unpinlatch (bt->latch);
          return 0;
        }

        // check if page has enough space

        if( slot = bt_cleanpage (bt, len, slot) )
                break;

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

  // calculate next available slot and copy key into page

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

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

  // now insert key into array before slot
  // preserving the fence slot

  if( idx == page->cnt )
        idx++, page->cnt++;

  page->act++;

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

  bt_putid(slotptr(page,slot)->id, id);
  slotptr(page, slot)->off = page->min;
#ifdef USETOD
  slotptr(page, slot)->tod = tod;
#endif
  slotptr(page, slot)->dead = 0;

  bt_update(bt, bt->page);

  bt_unlockpage(BtLockWrite, bt->latch);
  bt_unpinlatch(bt->latch);
  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)
{
uint slot;

        // cache page for retrieval

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

        bt_unlockpage(BtLockRead, bt->latch);
        bt->cursor_page = bt->page_no;
        bt_unpinlatch (bt->latch);
        return slot;
}

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

uint bt_nextkey (BtDb *bt, uint slot)
{
BtLatchSet *latch;
off64_t 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))
                return slot;
          else
                break;

        if( !right )
                break;

        bt->cursor_page = right;

        if( latch = bt_pinlatch (bt, right) )
        bt_lockpage(BtLockRead, latch);
        else
                return 0;

        bt->page = bt_mappage (bt, latch);
        memcpy (bt->cursor, bt->page, bt->page_size);
        bt_unlockpage(BtLockRead, latch);
        bt_unpinlatch (latch);
        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);
}

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

#ifdef STANDALONE

uint bt_audit (BtDb *bt)
{
uint idx, hashidx;
uid next, page_no;
BtLatchSet *latch;
uint blks[64];
uint cnt = 0;
BtPage page;
uint amt[1];
BtKey ptr;

#ifdef unix
        posix_fadvise( bt->idx, 0, 0, POSIX_FADV_SEQUENTIAL);
#endif
        if( *(ushort *)(bt->latchmgr->lock) )
                fprintf(stderr, "Alloc page locked\n");
        *(ushort *)(bt->latchmgr->lock) = 0;

        memset (blks, 0, sizeof(blks));

        for( idx = 1; idx <= bt->latchmgr->latchdeployed; idx++ ) {
                latch = bt->latchsets + idx;
                if( *(ushort *)latch->readwr )
                        fprintf(stderr, "latchset %d rwlocked for page %.8x\n", idx, latch->page_no);
                *(ushort *)latch->readwr = 0;

                if( *(ushort *)latch->access )
                        fprintf(stderr, "latchset %d accesslocked for page %.8x\n", idx, latch->page_no);
                *(ushort *)latch->access = 0;

                if( *(ushort *)latch->parent )
                        fprintf(stderr, "latchset %d parentlocked for page %.8x\n", idx, latch->page_no);
                *(ushort *)latch->parent = 0;

                if( latch->pin & PIN_mask ) {
                        fprintf(stderr, "latchset %d pinned for page %.8x\n", idx, latch->page_no);
                        latch->pin = 0;
                }
                page = (BtPage)((uid)idx * bt->page_size + bt->pagepool);
                blks[page->lvl]++;

            if( page->dirty )
                 if( bt_writepage (bt, page, latch->page_no) )
                        fprintf(stderr, "Page %.8x Write Error\n", latch->page_no);
        }

        for( idx = 0; blks[idx]; idx++ )
                fprintf(stderr, "cache: %d lvl %d blocks\n", blks[idx], idx);

        for( hashidx = 0; hashidx < bt->latchmgr->latchhash; hashidx++ ) {
          if( *(ushort *)(bt->table[hashidx].latch) )
                        fprintf(stderr, "hash entry %d locked\n", hashidx);

          *(ushort *)(bt->table[hashidx].latch) = 0;
        }

        memset (blks, 0, sizeof(blks));

        next = bt->latchmgr->nlatchpage + LATCH_page;
        page_no = LEAF_page;

        while( page_no < bt_getid(bt->latchmgr->alloc->right) ) {
                if( bt_readpage (bt, bt->frame, page_no) )
                  fprintf(stderr, "page %.8x unreadable\n", page_no);
                if( !bt->frame->free ) {
                 for( idx = 0; idx++ < bt->frame->cnt - 1; ) {
                  ptr = keyptr(bt->frame, idx+1);
                  if( keycmp (keyptr(bt->frame, idx), ptr->key, ptr->len) >= 0 )
                        fprintf(stderr, "page %.8x idx %.2x out of order\n", page_no, idx);
                 }
                 if( !bt->frame->lvl )
                        cnt += bt->frame->act;
                 blks[bt->frame->lvl]++;
                }

                if( page_no > LEAF_page )
                        next = page_no + 1;
                page_no = next;
        }

        for( idx = 0; blks[idx]; idx++ )
                fprintf(stderr, "btree: %d lvl %d blocks\n", blks[idx], idx);

        return cnt - 1;
}

#ifndef unix
double getCpuTime(int type)
{
FILETIME crtime[1];
FILETIME xittime[1];
FILETIME systime[1];
FILETIME usrtime[1];
SYSTEMTIME timeconv[1];
double ans = 0;

        memset (timeconv, 0, sizeof(SYSTEMTIME));

        switch( type ) {
        case 0:
                GetSystemTimeAsFileTime (xittime);
                FileTimeToSystemTime (xittime, timeconv);
                ans = (double)timeconv->wDayOfWeek * 3600 * 24;
                break;
        case 1:
                GetProcessTimes (GetCurrentProcess(), crtime, xittime, systime, usrtime);
                FileTimeToSystemTime (usrtime, timeconv);
                break;
        case 2:
                GetProcessTimes (GetCurrentProcess(), crtime, xittime, systime, usrtime);
                FileTimeToSystemTime (systime, timeconv);
                break;
        }

        ans += (double)timeconv->wHour * 3600;
        ans += (double)timeconv->wMinute * 60;
        ans += (double)timeconv->wSecond;
        ans += (double)timeconv->wMilliseconds / 1000;
        return ans;
}
#else
#include <time.h>
#include <sys/resource.h>

double getCpuTime(int type)
{
struct rusage used[1];
struct timeval tv[1];

        switch( type ) {
        case 0:
                gettimeofday(tv, NULL);
                return (double)tv->tv_sec + (double)tv->tv_usec / 1000000;

        case 1:
                getrusage(RUSAGE_SELF, used);
                return (double)used->ru_utime.tv_sec + (double)used->ru_utime.tv_usec / 1000000;

        case 2:
                getrusage(RUSAGE_SELF, used);
                return (double)used->ru_stime.tv_sec + (double)used->ru_stime.tv_usec / 1000000;
        }

        return 0;
}
#endif

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

int main (int argc, char **argv)
{
uint slot, line = 0, off = 0, found = 0;
int ch, cnt = 0, bits = 12, idx;
unsigned char key[256];
double done, start;
uid next, page_no;
BtLatchSet *latch;
float elapsed;
time_t tod[1];
uint scan = 0;
uint len = 0;
uint map = 0;
BtPage page;
BtKey ptr;
BtDb *bt;
FILE *in;

#ifdef WIN32
        _setmode (1, _O_BINARY);
#endif
        if( argc < 4 ) {
                fprintf (stderr, "Usage: %s idx_file src_file Read/Write/Scan/Delete/Find/Count [page_bits mapped_pool_pages start_line_number]\n", argv[0]);
                fprintf (stderr, "  page_bits: size of btree page in bits\n");
                fprintf (stderr, "  mapped_pool_pages: number of pages in buffer pool\n");
                exit(0);
        }

        start = getCpuTime(0);
        time(tod);

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

        if( argc > 5 )
                map = atoi(argv[5]);

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

        bt = bt_open ((argv[1]), BT_rw, bits, map);

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

        switch(argv[3][0]| 0x20)
        {
        case 'p':       // display page
                if( latch = bt_pinlatch (bt, off) )
                        page = bt_mappage (bt, latch);
                else
                        fprintf(stderr, "unable to read page %.8x\n", off);

                write (1, page, bt->page_size);
                break;

        case 'a':       // buffer pool audit
                fprintf(stderr, "started audit for %s\n", argv[1]);
                cnt = bt_audit (bt);
                fprintf(stderr, "finished audit for %s, %d keys\n", argv[1], cnt);
                break;

        case 'w':       // write keys
                fprintf(stderr, "started indexing for %s\n", argv[2]);
                if( argc > 2 && (in = fopen (argv[2], "rb")) ) {
#ifdef unix
                  posix_fadvise( fileno(in), 0, 0, POSIX_FADV_NOREUSE);
#endif
                  while( ch = getc(in), ch != EOF )
                        if( ch == '\n' )
                        {
                          if( off )
                                sprintf((char *)key+len, "%.9d", line + off), len += 9;

                          if( bt_insertkey (bt, key, len, 0, ++line, *tod) )
                                fprintf(stderr, "Error %d Line: %d\n", bt->err, line), exit(0);
                          len = 0;
                        }
                        else if( len < 245 )
                                key[len++] = ch;
                  }
                fprintf(stderr, "finished adding keys for %s, %d \n", argv[2], line);
                break;

        case 'd':       // delete keys
                fprintf(stderr, "started deleting keys for %s\n", argv[2]);
                if( argc > 2 && (in = fopen (argv[2], "rb")) ) {
#ifdef unix
                  posix_fadvise( fileno(in), 0, 0, POSIX_FADV_NOREUSE);
#endif
                  while( ch = getc(in), ch != EOF )
                        if( ch == '\n' )
                        {
                          if( off )
                                sprintf((char *)key+len, "%.9d", line + off), len += 9;
                          line++;
                          if( bt_deletekey (bt, key, len, 0) )
                                fprintf(stderr, "Error %d Line: %d\n", bt->err, line), exit(0);
                          len = 0;
                        }
                        else if( len < 245 )
                                key[len++] = ch;
                  }
                fprintf(stderr, "finished deleting keys for %s, %d \n", argv[2], line);
                break;

        case 'f':       // find keys
                fprintf(stderr, "started finding keys for %s\n", argv[2]);
                if( argc > 2 && (in = fopen (argv[2], "rb")) ) {
#ifdef unix
                  posix_fadvise( fileno(in), 0, 0, POSIX_FADV_NOREUSE);
#endif
                  while( ch = getc(in), ch != EOF )
                        if( ch == '\n' )
                        {
                          if( off )
                                sprintf((char *)key+len, "%.9d", line + off), len += 9;
                          line++;
                          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 < 245 )
                                key[len++] = ch;
                  }
                fprintf(stderr, "finished search of %d keys for %s, found %d\n", line, argv[2], found);
                break;

        case 's':       // scan and print keys
                fprintf(stderr, "started scaning\n");
                cnt = len = key[0] = 0;

                if( slot = bt_startkey (bt, key, len) )
                  slot--;
                else
                  fprintf(stderr, "Error %d in StartKey. Syserror: %d\n", bt->err, errno), exit(0);

                while( slot = bt_nextkey (bt, slot) ) {
                        ptr = bt_key(bt, slot);
                        fwrite (ptr->key, ptr->len, 1, stdout);
                        fputc ('\n', stdout);
                        cnt++;
                }

                fprintf(stderr, " Total keys read %d\n", cnt - 1);
                break;

        case 'c':       // count keys
          fprintf(stderr, "started counting\n");
          cnt = 0;

          next = bt->latchmgr->nlatchpage + LATCH_page;
          page_no = LEAF_page;

          while( page_no < bt_getid(bt->latchmgr->alloc->right) ) {
                if( latch = bt_pinlatch (bt, page_no) )
                        page = bt_mappage (bt, latch);
                if( !page->free && !page->lvl )
                        cnt += page->act;
                if( page_no > LEAF_page )
                        next = page_no + 1;
                if( scan )
                 for( idx = 0; idx++ < page->cnt; ) {
                  if( slotptr(page, idx)->dead )
                        continue;
                  ptr = keyptr(page, idx);
                  if( idx != page->cnt && bt_getid (page->right) ) {
                        fwrite (ptr->key, ptr->len, 1, stdout);
                        fputc ('\n', stdout);
                  }
                 }
                bt_unpinlatch (latch);
                page_no = next;
          }
                
          cnt--;        // remove stopper key
          fprintf(stderr, " Total keys read %d\n", cnt);
          break;
        }

        done = getCpuTime(0);
        elapsed = (float)(done - start);
        fprintf(stderr, " real %dm%.3fs\n", (int)(elapsed/60), elapsed - (int)(elapsed/60)*60);
        elapsed = getCpuTime(1);
        fprintf(stderr, " user %dm%.3fs\n", (int)(elapsed/60), elapsed - (int)(elapsed/60)*60);
        elapsed = getCpuTime(2);
        fprintf(stderr, " sys  %dm%.3fs\n", (int)(elapsed/60), elapsed - (int)(elapsed/60)*60);
        return 0;
}

#endif  //STANDALONE