SQLite4
Check-in [aabb6dacf6]
Not logged in

Many hyperlinks are disabled.
Use anonymous login to enable hyperlinks.

Overview
Comment:Updates to code to read log files.
Downloads: Tarball | ZIP archive | SQL archive
Timelines: family | ancestors | descendants | both | trunk
Files: files | file ages | folders
SHA1: aabb6dacf659c3c79fa20e73e96151dfb857e2d8
User & Date: dan 2013-10-24 19:59:05
Context
2013-10-24
23:54
Add tests for the pbReal output of sqlite4_num_from_text check-in: fd1c1a7d4f user: peterreid tags: trunk
19:59
Updates to code to read log files. check-in: aabb6dacf6 user: dan tags: trunk
2013-10-23
22:54
Prevent unnecessary rounding before multiplying check-in: 68dfaa3491 user: peterreid tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to lsm-test/lsmtest_tdb.c.

945
946
947
948
949
950
951

952


953
954
955
956
957
958
959
  };
  BtDb *p = 0;
  bt_db *pBt = 0;
  int rc;
  sqlite4_env *pEnv = sqlite4_env_default();

  if( bClear && zFilename && zFilename[0] ){

    unlink(zFilename);


  }
  
  rc = sqlite4BtNew(pEnv, sizeof(BtDb), &pBt);
  if( rc==SQLITE4_OK ){
    p = (BtDb*)sqlite4BtExtra(pBt);
    p->base.pMethods = &SqlMethods;
    p->pBt = pBt;







>

>
>







945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
  };
  BtDb *p = 0;
  bt_db *pBt = 0;
  int rc;
  sqlite4_env *pEnv = sqlite4_env_default();

  if( bClear && zFilename && zFilename[0] ){
    char *zLog = sqlite3_mprintf("%s-wal", zFilename);
    unlink(zFilename);
    unlink(zLog);
    sqlite3_free(zLog);
  }
  
  rc = sqlite4BtNew(pEnv, sizeof(BtDb), &pBt);
  if( rc==SQLITE4_OK ){
    p = (BtDb*)sqlite4BtExtra(pBt);
    p->base.pMethods = &SqlMethods;
    p->pBt = pBt;

Changes to src/bt_log.c.

34
35
36
37
38
39
40

41

42
43
44
45
46
47
48
..
51
52
53
54
55
56
57


58
59
60
61
62
63
64
...
236
237
238
239
240
241
242
243
244




































































































































































































































245
246
247
248










249

































250
251
252
253
254
255
256
...
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
...
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
...
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
...
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
...
529
530
531
532
533
534
535

536
537
538
539
540
541



542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
** byte offset 0 and the other at offset <sector-size> (the start of
** the second disk sector in the file, according to the xSectorSize
** VFS method).
*/
struct BtWalHdr {
  u32 iMagic;                     /* Magic number (BT_WAL_MAGIC) */
  u32 iVersion;                   /* File format version */

  u32 nSector;                    /* Sector size when header written */


  u32 iSalt1;                     /* Initial frame cksum-0 value */
  u32 iSalt2;                     /* Initial frame cksum-1 value */
  u32 iFirstFrame;                /* First frame of log (numbered from 1) */

  u32 aCksum[2];                  /* Checksum of all prior fields */
};
................................................................................
** WAL Frame header. All fields are stored in big-endian order.
*/
struct BtFrameHdr {
  u32 pgno;                       /* Page number of this frame */
  u32 ctrl;                       /* Next frame pointer and commit bit */
  u32 aCksum[2];                  /* Frame checksum */
};



/*
** Shared memory header. Shared memory begins with two copies of
** this structure. All fields are stored in machine byte-order.
*/
struct BtShmHdr {
  u32 aLog[6];                    /* First/last frames for each log region */
................................................................................
}

static void btLogZeroSnapshot(BtLog *pLog){
  bt_env *pVfs = pLog->pLock->pVfs;
  memset(&pLog->snapshot, 0, sizeof(BtShmHdr));
  pLog->snapshot.nSector = pVfs->xSectorSize(pLog->pFd);
}

/*




































































































































































































































** Run log recovery. In other words, read the log file from disk and 
** initialize the shared-memory accordingly.
*/
static int btLogRecover(BtLog *pLog){










  return SQLITE4_OK;

































}

/*
** Open the log file for pager pPager. If successful, return the BtLog* 
** handle via output variable *ppLog. If parameter bRecover is true, then
** also run database recovery before returning. In this case, the caller
** has already obtained the required locks.
................................................................................
    sqlite4_free(pEnv, pLog->apShm);
    sqlite4_free(pEnv, pLog);
  }

  return rc;
}

/*
** Return true if log is completely empty (as it is if a file zero bytes
** in size has been opened or created).
*/
static int btLogIsEmpty(BtLog *pLog){
  return (pLog->snapshot.aLog[4]==0);
}

static int btLogWriteData(BtLog *pLog, i64 iOff, u8 *aData, int nData){
  bt_env *pVfs = pLog->pLock->pVfs;
  return pVfs->xWrite(pLog->pFd, iOff, aData, nData);
}

static int btLogWriteHeader(BtLog *pLog, int iHdr, BtWalHdr *pHdr){
  int rc;                         /* Return code */
  i64 iOff;                       /* File offset to write to */
  assert( iHdr==0 || iHdr==1 );

  /* Calculate a checksum for the header */
  btLogChecksum(1, (u8*)pHdr, offsetof(BtWalHdr, aCksum), 0, pHdr->aCksum);
................................................................................
  /* Write the object to disk */
  iOff = iHdr * pLog->snapshot.nSector;
  rc = btLogWriteData(pLog, iOff, (u8*)pHdr, sizeof(BtWalHdr));

  return rc;
}

/*
** Locate the iHash'th hash table in shared memory. Return it.
*/
static int btLogFindHash(
  BtLog *pLog,                    /* Log handle */
  int iHash,                      /* Hash table (numbered from 0) to find */
  ht_slot **paHash,               /* OUT: Pointer to hash slots */
  u32 **paPgno,                   /* OUT: Pointer to page number array */
  u32 *piZero                     /* OUT: Frame associated with *paPgno[0] */
){
  int rc;

  rc = btLogMapShm(pLog, iHash);
  if( rc==SQLITE4_OK ){
    u8 *aChunk = pLog->apShm[iHash];
    u32 *aPgno;
    u32 iZero;

    *paHash = (ht_slot*)&aChunk[HASHTABLE_OFFSET_1];
    if( iHash==0 ){
      aPgno = (u32*)&aChunk[sizeof(BtShm)];
      iZero = 1;
    }else{
      aPgno = (u32*)aChunk;
      iZero = 1 + HASHTABLE_NFRAME_ONE + (HASHTABLE_NFRAME * (iHash-1));
    }
    *paPgno = aPgno;
    *piZero = iZero;
  }

  return rc;
}

/*
** Return the index of the hash table that contains the entry for frame
** iFrame. 
*/
static int btLogFrameHash(BtLog *pLog, u32 iFrame){
  if( iFrame<=HASHTABLE_NFRAME_ONE ) return 0;
  return 1 + ((iFrame - HASHTABLE_NFRAME_ONE - 1) / HASHTABLE_NFRAME);
}

/*
** Return a hash key for page number pgno.
*/
static int btLogHashKey(BtLog *pLog, u32 pgno){
  assert( pgno>=1 );
  return ((pgno * HASHTABLE_KEY_MUL) % HASHTABLE_NSLOT);
}

static int btLogHashNext(BtLog *pLog, int iSlot){
  return ((iSlot + 1) % HASHTABLE_NSLOT);
}

static int btLogHashSearch(BtLog *pLog, int iHash, u32 pgno, u32 *piFrame){
  ht_slot *aHash;
  u32 *aPgno;
  u32 iZero;
  int rc;

  rc = btLogFindHash(pLog, iHash, &aHash, &aPgno, &iZero);
................................................................................
    }
  }

  return rc;
}


/*
** Return the offset of frame iFrame within the log file.
*/
static i64 btLogFrameOffset(BtLog *pLog, int pgsz, u32 iFrame){
  return 
      (i64)pLog->snapshot.nSector*2 
    + (i64)(iFrame-1) * (i64)(pgsz + sizeof(BtFrameHdr));
}

/*
** Attempt to read data for page pgno from the log file. If successful,
** the data is written into buffer aData[] (which must be at least as
** large as a database page). In this case SQLITE4_OK is returned.
**
** If the log does not contain any version of page pgno, SQLITE4_NOTFOUND
** is returned and the contents of buffer aData[] are not modified.
................................................................................
    fflush(stderr);
#endif
  }

  return rc;
}

/*
** Add an entry mapping database page pgno to log frame iFrame to the
** the shared hash table. Return SQLITE4_OK if successful, or an SQLite4
** error code if an error occurs.
*/
static int btLogHashInsert(BtLog *pLog, u32 pgno, u32 iFrame){
  int iHash;                      /* Index of hash table to update */
  int rc = SQLITE4_OK;            /* Return code */
  ht_slot *aHash;                 /* Hash slots */
  u32 *aPgno;                     /* Page array for updated hash table */
  u32 iZero;                      /* Zero-offset of updated hash table */

  assert( iFrame>=1 && pgno>=1 );
  assert( iFrame==(pLog->snapshot.aLog[5]+1) );

  /* Find the required hash table */
  iHash = btLogFrameHash(pLog, iFrame);
  rc = btLogFindHash(pLog, iHash, &aHash, &aPgno, &iZero);

  /* Update the hash table */
  if( rc==SQLITE4_OK ){
    int iSlot;
    int nCollide = HASHTABLE_NSLOT*2;
    aPgno[iFrame-iZero] = pgno;

    for(iSlot=btLogHashKey(pLog,pgno); ; iSlot=btLogHashNext(pLog, iSlot)){
      if( aHash[iSlot]==0 ){
        aHash[iSlot] = (iFrame-iZero+1);
        break;
      }
      if( (nCollide--)==0 ) return btErrorBkpt(SQLITE4_CORRUPT);
    }
  }

  return rc;
}

/*
** Write a frame to the log file.
*/
int sqlite4BtLogWrite(BtLog *pLog, u32 pgno, u8 *aData, int bCommit){
  const int pgsz = sqlite4BtPagerPagesize((BtPager*)(pLog->pLock));
  int rc = SQLITE4_OK;
  u32 iFrame;                     /* Write this frame (numbered from 1) */
................................................................................
  if( btLogIsEmpty(pLog) ){
    BtWalHdr hdr;
    memset(&hdr, 0, sizeof(BtWalHdr));

    hdr.iMagic = BT_WAL_MAGIC;
    hdr.iVersion = BT_WAL_VERSION;
    hdr.nSector = pLog->snapshot.nSector;

    hdr.iSalt1 = 22;
    hdr.iSalt2 = 23;
    hdr.iFirstFrame = 1;

    rc = btLogWriteHeader(pLog, 0, &hdr);
    if( rc!=SQLITE4_OK ) return rc;



  }

  /* Figure out where exactly to write the new data */
  iFrame = pLog->snapshot.aLog[5] + 1;
  iOff = btLogFrameOffset(pLog, pgsz, iFrame);

  /* Populate the frame header object. */
  memset(&frame, 0, sizeof(frame));
  frame.pgno = pgno;
  frame.ctrl = (bCommit ? 0x80000000 : 0x00000000);
  a = pLog->snapshot.aFrameCksum;
  btLogChecksum(1, (u8*)&frame, offsetof(BtFrameHdr, aCksum), a, frame.aCksum);
  btLogChecksum(1, aData, pgsz, frame.aCksum, frame.aCksum);

#if 0
fprintf(stderr, "writing page %d at log offset %d (frame %d)\n", (int)pgno, (int)iOff, (int)iFrame);
fflush(stderr);







>

>







 







>
>







 









>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>




>
>
>
>
>
>
>
>
>
>
|
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>







 







<
<
<
<
<
<
<
<
<
<
<
<
<







 







<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<







 







<
<
<
<
<
<
<
<
<







 







<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<







 







>






>
>
>









|







34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
..
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
...
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
...
588
589
590
591
592
593
594













595
596
597
598
599
600
601
...
603
604
605
606
607
608
609






















































610
611
612
613
614
615
616
...
633
634
635
636
637
638
639









640
641
642
643
644
645
646
...
671
672
673
674
675
676
677





































678
679
680
681
682
683
684
...
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
** byte offset 0 and the other at offset <sector-size> (the start of
** the second disk sector in the file, according to the xSectorSize
** VFS method).
*/
struct BtWalHdr {
  u32 iMagic;                     /* Magic number (BT_WAL_MAGIC) */
  u32 iVersion;                   /* File format version */
  u32 iCnt;                       /* 0, 1 or 2 */
  u32 nSector;                    /* Sector size when header written */
  u32 nPgsz;                      /* Database page size in bytes */

  u32 iSalt1;                     /* Initial frame cksum-0 value */
  u32 iSalt2;                     /* Initial frame cksum-1 value */
  u32 iFirstFrame;                /* First frame of log (numbered from 1) */

  u32 aCksum[2];                  /* Checksum of all prior fields */
};
................................................................................
** WAL Frame header. All fields are stored in big-endian order.
*/
struct BtFrameHdr {
  u32 pgno;                       /* Page number of this frame */
  u32 ctrl;                       /* Next frame pointer and commit bit */
  u32 aCksum[2];                  /* Frame checksum */
};

#define BT_FRAME_COMMIT 0x80000000

/*
** Shared memory header. Shared memory begins with two copies of
** this structure. All fields are stored in machine byte-order.
*/
struct BtShmHdr {
  u32 aLog[6];                    /* First/last frames for each log region */
................................................................................
}

static void btLogZeroSnapshot(BtLog *pLog){
  bt_env *pVfs = pLog->pLock->pVfs;
  memset(&pLog->snapshot, 0, sizeof(BtShmHdr));
  pLog->snapshot.nSector = pVfs->xSectorSize(pLog->pFd);
}

/*
** Return the offset of frame iFrame within the log file.
*/
static i64 btLogFrameOffset(BtLog *pLog, int pgsz, u32 iFrame){
  return 
      (i64)pLog->snapshot.nSector*2 
    + (i64)(iFrame-1) * (i64)(pgsz + sizeof(BtFrameHdr));
}

static int btLogWriteData(BtLog *pLog, i64 iOff, u8 *aData, int nData){
  bt_env *pVfs = pLog->pLock->pVfs;
  return pVfs->xWrite(pLog->pFd, iOff, aData, nData);
}

static int btLogReadData(BtLog *pLog, i64 iOff, u8 *aData, int nData){
  bt_env *pVfs = pLog->pLock->pVfs;
  return pVfs->xRead(pLog->pFd, iOff, aData, nData);
}

static int btLogReadHeader(BtLog *pLog, int iOff, BtWalHdr *pHdr){
  int rc = btLogReadData(pLog, (i64)iOff, (u8*)pHdr, sizeof(BtWalHdr));
  if( rc==SQLITE4_OK ){
    u32 aCksum[2];
    btLogChecksum(1, (u8*)pHdr, offsetof(BtWalHdr, aCksum), 0, aCksum);
    if( pHdr->iMagic!=BT_WAL_MAGIC 
     || aCksum[0]!=pHdr->aCksum[0] 
     || aCksum[1]!=pHdr->aCksum[1] 
    ){
      rc = SQLITE4_NOTFOUND;
    }
  }
  return rc;
}

/*
** This function is used as part of recovery. It reads the contents of
** the log file from disk and invokes the xFrame callback for each valid
** frame in the file.
*/
static int btLogTraverse(
  BtLog *pLog,                    /* Log module handle */
  BtWalHdr *pHdr,                 /* Log header read from file */
  int(*xFrame)(BtLog*, void*, u32, BtFrameHdr*), /* Frame callback */
  void *pCtx                      /* Passed as second argument to xFrame */
){
  sqlite4_env *pEnv = pLog->pLock->pEnv;
  const int pgsz = pHdr->nPgsz;
  u32 iFrame = pHdr->iFirstFrame;
  u32 aCksum[2];
  BtFrameHdr fhdr;                /* Frame header */
  u8 *aBuf;                       /* Buffer for frame data */
  int rc = SQLITE4_OK;

  aCksum[0] = pHdr->iSalt1;
  aCksum[1] = pHdr->iSalt2;

  aBuf = sqlite4_malloc(pEnv, pgsz);
  if( aBuf==0 ){
    rc = SQLITE4_NOMEM;
  }

  while( rc==SQLITE4_OK ){
    i64 iOff;
    iOff = btLogFrameOffset(pLog, pgsz, iFrame);

    rc = btLogReadData(pLog, iOff, (u8*)&fhdr, sizeof(BtFrameHdr));
    if( rc==SQLITE4_OK ){
      rc = btLogReadData(pLog, iOff+sizeof(BtFrameHdr), aBuf, pgsz);
    }
    if( rc==SQLITE4_OK ){
      btLogChecksum(1, (u8*)&fhdr, offsetof(BtFrameHdr,aCksum), aCksum, aCksum);
      btLogChecksum(1, aBuf, pgsz, aCksum, aCksum);
      if( aCksum[0]!=fhdr.aCksum[0] || aCksum[1]!=fhdr.aCksum[1] ) break;
    }
    if( rc==SQLITE4_OK ){
      rc = xFrame(pLog, pCtx, iFrame, &fhdr);
    }

    iFrame++;
  }

  return rc;
}

/*
** Locate the iHash'th hash table in shared memory. Return it.
*/
static int btLogFindHash(
  BtLog *pLog,                    /* Log handle */
  int iHash,                      /* Hash table (numbered from 0) to find */
  ht_slot **paHash,               /* OUT: Pointer to hash slots */
  u32 **paPgno,                   /* OUT: Pointer to page number array */
  u32 *piZero                     /* OUT: Frame associated with *paPgno[0] */
){
  int rc;

  rc = btLogMapShm(pLog, iHash);
  if( rc==SQLITE4_OK ){
    u8 *aChunk = pLog->apShm[iHash];
    u32 *aPgno;
    u32 iZero;

    *paHash = (ht_slot*)&aChunk[HASHTABLE_OFFSET_1];
    if( iHash==0 ){
      aPgno = (u32*)&aChunk[sizeof(BtShm)];
      iZero = 1;
    }else{
      aPgno = (u32*)aChunk;
      iZero = 1 + HASHTABLE_NFRAME_ONE + (HASHTABLE_NFRAME * (iHash-1));
    }
    *paPgno = aPgno;
    *piZero = iZero;
  }

  return rc;
}


/*
** Return the index of the hash table that contains the entry for frame
** iFrame. 
*/
static int btLogFrameHash(BtLog *pLog, u32 iFrame){
  if( iFrame<=HASHTABLE_NFRAME_ONE ) return 0;
  return 1 + ((iFrame - HASHTABLE_NFRAME_ONE - 1) / HASHTABLE_NFRAME);
}

/*
** Return a hash key for page number pgno.
*/
static int btLogHashKey(BtLog *pLog, u32 pgno){
  assert( pgno>=1 );
  return ((pgno * HASHTABLE_KEY_MUL) % HASHTABLE_NSLOT);
}

static int btLogHashNext(BtLog *pLog, int iSlot){
  return ((iSlot + 1) % HASHTABLE_NSLOT);
}

/*
** Add an entry mapping database page pgno to log frame iFrame to the
** the shared hash table. Return SQLITE4_OK if successful, or an SQLite4
** error code if an error occurs.
*/
static int btLogHashInsert(BtLog *pLog, u32 pgno, u32 iFrame){
  int iHash;                      /* Index of hash table to update */
  int rc = SQLITE4_OK;            /* Return code */
  ht_slot *aHash;                 /* Hash slots */
  u32 *aPgno;                     /* Page array for updated hash table */
  u32 iZero;                      /* Zero-offset of updated hash table */

  assert( iFrame>=1 && pgno>=1 );

  /* Find the required hash table */
  iHash = btLogFrameHash(pLog, iFrame);
  rc = btLogFindHash(pLog, iHash, &aHash, &aPgno, &iZero);

  /* Update the hash table */
  if( rc==SQLITE4_OK ){
    int iSlot;
    int nCollide = HASHTABLE_NSLOT*2;
    aPgno[iFrame-iZero] = pgno;

    for(iSlot=btLogHashKey(pLog,pgno); ; iSlot=btLogHashNext(pLog, iSlot)){
      if( aHash[iSlot]==0 ){
        aHash[iSlot] = (iFrame-iZero+1);
        break;
      }
      if( (nCollide--)==0 ) return btErrorBkpt(SQLITE4_CORRUPT);
    }
  }

  return rc;
}

/*
** Remove everything following frame iFrame from the iHash'th hash table.
*/
static int btLogHashRollback(BtLog *pLog, int iHash, u32 iFrame){
  const int nPgno = (iHash==0 ? HASHTABLE_NFRAME_ONE : HASHTABLE_NFRAME);
  ht_slot *aHash;                 /* Hash slots */
  u32 *aPgno;                     /* Page array for updated hash table */
  u32 iZero;                      /* Zero-offset of updated hash table */
  int rc;

  rc = btLogFindHash(pLog, iHash, &aHash, &aPgno, &iZero);
  if( rc==SQLITE4_OK ){
    int i;
    ht_slot iMax;
    iMax = (iFrame - iZero) + 1;

    for(i=0; i<HASHTABLE_NSLOT; i++){
      if( aHash[i]>iMax ) aHash[i] = 0;
    }
    memset(&aPgno[iMax], 0, (nPgno-iMax)*sizeof(u32));
  }

  return rc;
}


/*
** Return true if log is completely empty (as it is if a file zero bytes
** in size has been opened or created).
*/
static int btLogIsEmpty(BtLog *pLog){
  return (pLog->snapshot.aLog[4]==0);
}

static int btLogRecoverFrame(
  BtLog *pLog,                    /* Log module handle */
  void *pCtx,                     /* woints to type u32 - pgno of last commit*/
  u32 iFrame,                     /* Frame number */
  BtFrameHdr *pHdr                /* Frame header */
){
  btLogHashInsert(pLog, pHdr->pgno, iFrame);
  if( pHdr->ctrl & BT_FRAME_COMMIT ){
    *(u32*)pCtx = iFrame;
    memcpy(pLog->snapshot.aFrameCksum, pHdr->aCksum, sizeof(pHdr->aCksum));
  }

#if 0
  fprintf(stderr, "recovered frame=%d pgno=%d\n", iFrame, pHdr->pgno);
  fflush(stderr);
#endif
  return 0;
}

/*
** Run log recovery. In other words, read the log file from disk and 
** initialize the shared-memory accordingly.
*/
static int btLogRecover(BtLog *pLog){
  bt_env *pVfs = pLog->pLock->pVfs;
  i64 nByte = 0;                  /* Size of log file on disk */
  int rc;                         /* Return code */
  BtWalHdr *pHdr = 0;

  /* Read a log file header from the start of the file. */
  rc = pVfs->xSize(pLog->pFd, &nByte);
  if( rc==SQLITE4_OK && nByte>0 ){
    BtWalHdr hdr1;
    rc = btLogReadHeader(pLog, 0, &hdr1);
    if( rc==SQLITE4_OK ){
      BtWalHdr hdr2;
      rc = btLogReadHeader(pLog, hdr1.nSector, &hdr2);
      if( rc==SQLITE4_NOTFOUND ){
        pHdr = &hdr1;
      }else if( rc==SQLITE4_OK ){
        int aGreater[3] = {1, 2, 0};
        pHdr = ((hdr2.iCnt==aGreater[hdr1.iCnt]) ? &hdr2 : &hdr1);
      }
    }else if( rc==SQLITE4_NOTFOUND ){
      int iOff;
      for(iOff=256; iOff<=65536 && rc==SQLITE4_NOTFOUND; iOff=iOff*2){
        rc = btLogReadHeader(pLog, iOff, &hdr1);
      }
      if( rc==SQLITE4_OK ){
        pHdr = &hdr1;
      }
    }
    if( rc==SQLITE4_NOTFOUND ) rc = SQLITE4_OK;
  }

  /* If a header was successfully read from the file, scan the log file
  ** and populate the shared-memory hash tables.  */
  if( pHdr ){
    u32 iCommit = 0;
    rc = btLogTraverse(pLog, pHdr, btLogRecoverFrame, (void*)&iCommit);
    if( rc==SQLITE4_OK && iCommit>0 ){
      pLog->snapshot.aLog[4] = 1;
      pLog->snapshot.aLog[5] = iCommit;
      rc = btLogHashRollback(pLog, btLogFrameHash(pLog, iCommit), iCommit);
    }
  }

  return rc;
}

/*
** Open the log file for pager pPager. If successful, return the BtLog* 
** handle via output variable *ppLog. If parameter bRecover is true, then
** also run database recovery before returning. In this case, the caller
** has already obtained the required locks.
................................................................................
    sqlite4_free(pEnv, pLog->apShm);
    sqlite4_free(pEnv, pLog);
  }

  return rc;
}














static int btLogWriteHeader(BtLog *pLog, int iHdr, BtWalHdr *pHdr){
  int rc;                         /* Return code */
  i64 iOff;                       /* File offset to write to */
  assert( iHdr==0 || iHdr==1 );

  /* Calculate a checksum for the header */
  btLogChecksum(1, (u8*)pHdr, offsetof(BtWalHdr, aCksum), 0, pHdr->aCksum);
................................................................................
  /* Write the object to disk */
  iOff = iHdr * pLog->snapshot.nSector;
  rc = btLogWriteData(pLog, iOff, (u8*)pHdr, sizeof(BtWalHdr));

  return rc;
}























































static int btLogHashSearch(BtLog *pLog, int iHash, u32 pgno, u32 *piFrame){
  ht_slot *aHash;
  u32 *aPgno;
  u32 iZero;
  int rc;

  rc = btLogFindHash(pLog, iHash, &aHash, &aPgno, &iZero);
................................................................................
    }
  }

  return rc;
}











/*
** Attempt to read data for page pgno from the log file. If successful,
** the data is written into buffer aData[] (which must be at least as
** large as a database page). In this case SQLITE4_OK is returned.
**
** If the log does not contain any version of page pgno, SQLITE4_NOTFOUND
** is returned and the contents of buffer aData[] are not modified.
................................................................................
    fflush(stderr);
#endif
  }

  return rc;
}






































/*
** Write a frame to the log file.
*/
int sqlite4BtLogWrite(BtLog *pLog, u32 pgno, u8 *aData, int bCommit){
  const int pgsz = sqlite4BtPagerPagesize((BtPager*)(pLog->pLock));
  int rc = SQLITE4_OK;
  u32 iFrame;                     /* Write this frame (numbered from 1) */
................................................................................
  if( btLogIsEmpty(pLog) ){
    BtWalHdr hdr;
    memset(&hdr, 0, sizeof(BtWalHdr));

    hdr.iMagic = BT_WAL_MAGIC;
    hdr.iVersion = BT_WAL_VERSION;
    hdr.nSector = pLog->snapshot.nSector;
    hdr.nPgsz = pgsz;
    hdr.iSalt1 = 22;
    hdr.iSalt2 = 23;
    hdr.iFirstFrame = 1;

    rc = btLogWriteHeader(pLog, 0, &hdr);
    if( rc!=SQLITE4_OK ) return rc;

    pLog->snapshot.aFrameCksum[0] = hdr.iSalt1;
    pLog->snapshot.aFrameCksum[1] = hdr.iSalt2;
  }

  /* Figure out where exactly to write the new data */
  iFrame = pLog->snapshot.aLog[5] + 1;
  iOff = btLogFrameOffset(pLog, pgsz, iFrame);

  /* Populate the frame header object. */
  memset(&frame, 0, sizeof(frame));
  frame.pgno = pgno;
  frame.ctrl = (bCommit ? BT_FRAME_COMMIT : 0);
  a = pLog->snapshot.aFrameCksum;
  btLogChecksum(1, (u8*)&frame, offsetof(BtFrameHdr, aCksum), a, frame.aCksum);
  btLogChecksum(1, aData, pgsz, frame.aCksum, frame.aCksum);

#if 0
fprintf(stderr, "writing page %d at log offset %d (frame %d)\n", (int)pgno, (int)iOff, (int)iFrame);
fflush(stderr);