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Overview
Comment:Performance optimization to pageFindSlot() in the b-tree layer.
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SHA3-256:59560d079fab4b91ec50855cc60349da178209c38fb6dae674ff874ccfc7f5fa
User & Date: drh 2017-08-23 23:09:03
References
2017-08-25
13:02
Convert a branch made unreachable by [59560d07] into an assert(). check-in: 2738b8db user: drh tags: trunk
Context
2017-08-24
13:55
Make sure the sqlite3_result_pointer() interface does not leave a VM register in an inconsistent state. Fix for ticket [7486aa54b968e9b5]. Test cases are in TH3. check-in: d2f9230c user: drh tags: trunk
2017-08-23
23:09
Performance optimization to pageFindSlot() in the b-tree layer. check-in: 59560d07 user: drh tags: trunk
20:36
Size and performance optimization to dropCell() and freeSpace(). check-in: bc1ec123 user: drh tags: trunk
Changes
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Changes to src/btree.c.

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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_PGNO(pPg->pgno);
      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 );
................................................................................
         ** 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[]







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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;
  int size;            /* Size of the free slot */

  assert( pc>0 );




  while( pc<=usableSize-4 ){



    /* 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 );
................................................................................
         ** for the portion used by the new allocation. */
        put2byte(&aData[pc+2], x);
      }
      return &aData[pc + x];
    }
    iAddr = pc;
    pc = get2byte(&aData[pc]);
    if( pc<iAddr+size ) break;
  }
  if( pc ){
    *pRc = SQLITE_CORRUPT_PGNO(pPg->pgno);
  }

  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[]