SQLite

Check-in [78da0f69cb]
Login

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

Overview
Comment:More simplifications and performance improvements to cell allocation logic associated with allocateSpace().
Downloads: Tarball | ZIP archive
Timelines: family | ancestors | descendants | both | trunk
Files: files | file ages | folders
SHA1: 78da0f69cb3289e332018864004f319f2764a5c8
User & Date: drh 2015-06-25 18:36:13.826
Context
2015-06-25
19:53
Simplifications and performance improvements in insertCell(). (check-in: 7d02e6c992 user: drh tags: trunk)
18:36
More simplifications and performance improvements to cell allocation logic associated with allocateSpace(). (check-in: 78da0f69cb user: drh tags: trunk)
16:01
Reorder the terms of a conditional for a small performance gain. (check-in: d67b0ed105 user: drh tags: trunk)
Changes
Unified Diff Ignore Whitespace Patch
Changes to src/btree.c.
1347
1348
1349
1350
1351
1352
1353
1354

1355
1356
1357
1358
1359
1360
1361

1362
1363
1364
1365


1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401


1402
1403
1404
1405
1406
1407
1408
1409
** from the free-list.
**
** If no suitable space can be found on the free-list, return NULL.
**
** This function may detect corruption within pPg.  If corruption is
** detected then *pRc is set to SQLITE_CORRUPT and NULL is returned.
**
** If a slot of at least nByte bytes is found but cannot be used because 

** there are already at least 60 fragmented bytes on the page, return NULL.
** In this case, if pbDefrag parameter is not NULL, set *pbDefrag to true.
*/
static u8 *pageFindSlot(MemPage *pPg, int nByte, int *pRc, int *pbDefrag){
  const int hdr = pPg->hdrOffset;
  u8 * const aData = pPg->aData;
  int iAddr;

  int pc;
  int usableSize = pPg->pBt->usableSize;

  for(iAddr=hdr+1; (pc = get2byte(&aData[iAddr]))>0; iAddr=pc){


    int size;            /* Size of the free slot */
    /* EVIDENCE-OF: R-06866-39125 Freeblocks are always connected in order of
    ** increasing offset. */
    if( pc>usableSize-4 || pc<iAddr+4 ){
      *pRc = SQLITE_CORRUPT_BKPT;
      return 0;
    }
    /* EVIDENCE-OF: R-22710-53328 The third and fourth bytes of each
    ** freeblock form a big-endian integer which is the size of the freeblock
    ** in bytes, including the 4-byte header. */
    size = get2byte(&aData[pc+2]);
    if( size>=nByte ){
      int x = size - nByte;
      testcase( x==4 );
      testcase( x==3 );
      if( pc < pPg->cellOffset+2*pPg->nCell || size+pc > usableSize ){
        *pRc = SQLITE_CORRUPT_BKPT;
        return 0;
      }else if( x<4 ){
        /* EVIDENCE-OF: R-11498-58022 In a well-formed b-tree page, the total
        ** number of bytes in fragments may not exceed 60. */
        if( aData[hdr+7]>=60 ){
          if( pbDefrag ) *pbDefrag = 1;
          return 0;
        }
        /* Remove the slot from the free-list. Update the number of
        ** fragmented bytes within the page. */
        memcpy(&aData[iAddr], &aData[pc], 2);
        aData[hdr+7] += (u8)x;
      }else{
        /* The slot remains on the free-list. Reduce its size to account
         ** for the portion used by the new allocation. */
        put2byte(&aData[pc+2], x);
      }
      return &aData[pc + x];
    }


  }

  return 0;
}

/*
** Allocate nByte bytes of space from within the B-Tree page passed
** as the first argument. Write into *pIdx the index into pPage->aData[]







|
>
|
<

|


|
>
|


<
>
>











<
|








|
<
<
|











>
>
|







1347
1348
1349
1350
1351
1352
1353
1354
1355
1356

1357
1358
1359
1360
1361
1362
1363
1364
1365

1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378

1379
1380
1381
1382
1383
1384
1385
1386
1387
1388


1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
** from the free-list.
**
** If no suitable space can be found on the free-list, return NULL.
**
** This function may detect corruption within pPg.  If corruption is
** detected then *pRc is set to SQLITE_CORRUPT and NULL is returned.
**
** Slots on the free list that are between 1 and 3 bytes larger than nByte
** will be ignored if adding the extra space to the fragmentation count
** causes the fragmentation count to exceed 60.

*/
static u8 *pageFindSlot(MemPage *pPg, int nByte, int *pRc){
  const int hdr = pPg->hdrOffset;
  u8 * const aData = pPg->aData;
  int iAddr = hdr + 1;
  int pc = get2byte(&aData[iAddr]);
  int x;
  int usableSize = pPg->pBt->usableSize;


  assert( pc>0 );
  do{
    int size;            /* Size of the free slot */
    /* EVIDENCE-OF: R-06866-39125 Freeblocks are always connected in order of
    ** increasing offset. */
    if( pc>usableSize-4 || pc<iAddr+4 ){
      *pRc = SQLITE_CORRUPT_BKPT;
      return 0;
    }
    /* EVIDENCE-OF: R-22710-53328 The third and fourth bytes of each
    ** freeblock form a big-endian integer which is the size of the freeblock
    ** in bytes, including the 4-byte header. */
    size = get2byte(&aData[pc+2]);

    if( (x = size - nByte)>=0 ){
      testcase( x==4 );
      testcase( x==3 );
      if( pc < pPg->cellOffset+2*pPg->nCell || size+pc > usableSize ){
        *pRc = SQLITE_CORRUPT_BKPT;
        return 0;
      }else if( x<4 ){
        /* EVIDENCE-OF: R-11498-58022 In a well-formed b-tree page, the total
        ** number of bytes in fragments may not exceed 60. */
        if( aData[hdr+7]>57 ) return 0;



        /* Remove the slot from the free-list. Update the number of
        ** fragmented bytes within the page. */
        memcpy(&aData[iAddr], &aData[pc], 2);
        aData[hdr+7] += (u8)x;
      }else{
        /* The slot remains on the free-list. Reduce its size to account
         ** for the portion used by the new allocation. */
        put2byte(&aData[pc+2], x);
      }
      return &aData[pc + x];
    }
    iAddr = pc;
    pc = get2byte(&aData[pc]);
  }while( pc );

  return 0;
}

/*
** Allocate nByte bytes of space from within the B-Tree page passed
** as the first argument. Write into *pIdx the index into pPage->aData[]
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468


1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
  ** array entry offset, and if the freelist is not empty, then search the
  ** freelist looking for a free slot big enough to satisfy the request.
  */
  testcase( gap+2==top );
  testcase( gap+1==top );
  testcase( gap==top );
  if( (data[hdr+2] || data[hdr+1]) && gap+2<=top ){
    int bDefrag = 0;
    u8 *pSpace = pageFindSlot(pPage, nByte, &rc, &bDefrag);
    if( rc ) return rc;
    if( bDefrag ) goto defragment_page;
    if( pSpace ){
      assert( pSpace>=data && (pSpace - data)<65536 );
      *pIdx = (int)(pSpace - data);
      return SQLITE_OK;


    }
  }

  /* The request could not be fulfilled using a freelist slot.  Check
  ** to see if defragmentation is necessary.
  */
  testcase( gap+2+nByte==top );
  if( gap+2+nByte>top ){
 defragment_page:
    assert( pPage->nCell>0 || CORRUPT_DB );
    rc = defragmentPage(pPage);
    if( rc ) return rc;
    top = get2byteNotZero(&data[hdr+5]);
    assert( gap+nByte<=top );
  }








<
|
<
<




>
>








<







1455
1456
1457
1458
1459
1460
1461

1462


1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476

1477
1478
1479
1480
1481
1482
1483
  ** array entry offset, and if the freelist is not empty, then search the
  ** freelist looking for a free slot big enough to satisfy the request.
  */
  testcase( gap+2==top );
  testcase( gap+1==top );
  testcase( gap==top );
  if( (data[hdr+2] || data[hdr+1]) && gap+2<=top ){

    u8 *pSpace = pageFindSlot(pPage, nByte, &rc);


    if( pSpace ){
      assert( pSpace>=data && (pSpace - data)<65536 );
      *pIdx = (int)(pSpace - data);
      return SQLITE_OK;
    }else if( rc ){
      return rc;
    }
  }

  /* The request could not be fulfilled using a freelist slot.  Check
  ** to see if defragmentation is necessary.
  */
  testcase( gap+2+nByte==top );
  if( gap+2+nByte>top ){

    assert( pPage->nCell>0 || CORRUPT_DB );
    rc = defragmentPage(pPage);
    if( rc ) return rc;
    top = get2byteNotZero(&data[hdr+5]);
    assert( gap+nByte<=top );
  }

6410
6411
6412
6413
6414
6415
6416
6417
6418
6419
6420
6421
6422
6423
6424
6425
6426
6427
6428
6429
6430
6431
  int iFirst,                     /* Index of first cell to add */
  int nCell,                      /* Number of cells to add to pPg */
  CellArray *pCArray              /* Array of cells */
){
  int i;
  u8 *aData = pPg->aData;
  u8 *pData = *ppData;
  const int bFreelist = aData[1] || aData[2];
  int iEnd = iFirst + nCell;
  assert( CORRUPT_DB || pPg->hdrOffset==0 );    /* Never called on page 1 */
  for(i=iFirst; i<iEnd; i++){
    int sz, rc;
    u8 *pSlot;
    sz = cachedCellSize(pCArray, i);
    if( bFreelist==0 || (pSlot = pageFindSlot(pPg, sz, &rc, 0))==0 ){
      pData -= sz;
      if( pData<pBegin ) return 1;
      pSlot = pData;
    }
    memcpy(pSlot, pCArray->apCell[i], sz);
    put2byte(pCellptr, (pSlot - aData));
    pCellptr += 2;







<






|







6409
6410
6411
6412
6413
6414
6415

6416
6417
6418
6419
6420
6421
6422
6423
6424
6425
6426
6427
6428
6429
  int iFirst,                     /* Index of first cell to add */
  int nCell,                      /* Number of cells to add to pPg */
  CellArray *pCArray              /* Array of cells */
){
  int i;
  u8 *aData = pPg->aData;
  u8 *pData = *ppData;

  int iEnd = iFirst + nCell;
  assert( CORRUPT_DB || pPg->hdrOffset==0 );    /* Never called on page 1 */
  for(i=iFirst; i<iEnd; i++){
    int sz, rc;
    u8 *pSlot;
    sz = cachedCellSize(pCArray, i);
    if( (aData[1]==0 && aData[2]==0) || (pSlot = pageFindSlot(pPg,sz,&rc))==0 ){
      pData -= sz;
      if( pData<pBegin ) return 1;
      pSlot = pData;
    }
    memcpy(pSlot, pCArray->apCell[i], sz);
    put2byte(pCellptr, (pSlot - aData));
    pCellptr += 2;