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Overview
Comment:Performance optimization and very slight size reduction for OP_Column.
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SHA1:869c30e45cc87063be423c650f16b99e8adb3df0
User & Date: drh 2014-10-11 23:31:52
Context
2014-10-12
22:37
Remove the VdbeCursor.lastRowid cache of the current rowid, since maintaining the correct cache value uses more CPU cycles than just recomputing the rowid on the occasions when it is actually needed. Replace it with the VdbeCursor.aOffset field which used to be computed from VdbeCursor.aType when needed. Saves 100 bytes of code space and runs 0.2% faster. check-in: 91384a7d user: drh tags: trunk
2014-10-11
23:31
Performance optimization and very slight size reduction for OP_Column. check-in: 869c30e4 user: drh tags: trunk
17:22
Simplification to the insertCell() routine in btree.c, resulting in a performance boost and a very small size decrease. It turns out that the extra work involved in sometimes avoiding an memcpy() of the first four bytes of a record takes more time than just unconditionally copying those four bytes. check-in: 66de1558 user: drh tags: trunk
Changes
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Changes to src/vdbe.c.

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        goto too_big;
      }
    }
    pC->cacheStatus = p->cacheCtr;
    pC->iHdrOffset = getVarint32(pC->aRow, offset);
    pC->nHdrParsed = 0;
    aOffset[0] = offset;
    if( avail<offset ){
      /* pC->aRow does not have to hold the entire row, but it does at least
      ** need to cover the header of the record.  If pC->aRow does not contain
      ** the complete header, then set it to zero, forcing the header to be
      ** dynamically allocated. */
      pC->aRow = 0;
      pC->szRow = 0;
    }

    /* Make sure a corrupt database has not given us an oversize header.
    ** Do this now to avoid an oversize memory allocation.
    **
    ** Type entries can be between 1 and 5 bytes each.  But 4 and 5 byte
    ** types use so much data space that there can only be 4096 and 32 of
    ** them, respectively.  So the maximum header length results from a
................................................................................
    ** 3-byte type for each of the maximum of 32768 columns plus three
    ** extra bytes for the header length itself.  32768*3 + 3 = 98307.
    */
    if( offset > 98307 || offset > pC->payloadSize ){
      rc = SQLITE_CORRUPT_BKPT;
      goto op_column_error;
    }
















  }

  /* Make sure at least the first p2+1 entries of the header have been
  ** parsed and valid information is in aOffset[] and pC->aType[].
  */
  if( pC->nHdrParsed<=p2 ){
    /* If there is more header available for parsing in the record, try
    ** to extract additional fields up through the p2+1-th field 
    */

    if( pC->iHdrOffset<aOffset[0] ){
      /* Make sure zData points to enough of the record to cover the header. */
      if( pC->aRow==0 ){
        memset(&sMem, 0, sizeof(sMem));
        rc = sqlite3VdbeMemFromBtree(pCrsr, 0, aOffset[0], 
                                     !pC->isTable, &sMem);
        if( rc!=SQLITE_OK ){







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        goto too_big;
      }
    }
    pC->cacheStatus = p->cacheCtr;
    pC->iHdrOffset = getVarint32(pC->aRow, offset);
    pC->nHdrParsed = 0;
    aOffset[0] = offset;









    /* Make sure a corrupt database has not given us an oversize header.
    ** Do this now to avoid an oversize memory allocation.
    **
    ** Type entries can be between 1 and 5 bytes each.  But 4 and 5 byte
    ** types use so much data space that there can only be 4096 and 32 of
    ** them, respectively.  So the maximum header length results from a
................................................................................
    ** 3-byte type for each of the maximum of 32768 columns plus three
    ** extra bytes for the header length itself.  32768*3 + 3 = 98307.
    */
    if( offset > 98307 || offset > pC->payloadSize ){
      rc = SQLITE_CORRUPT_BKPT;
      goto op_column_error;
    }

    if( avail<offset ){
      /* pC->aRow does not have to hold the entire row, but it does at least
      ** need to cover the header of the record.  If pC->aRow does not contain
      ** the complete header, then set it to zero, forcing the header to be
      ** dynamically allocated. */
      pC->aRow = 0;
      pC->szRow = 0;
    }

    /* The following goto is an optimization.  It can be omitted and
    ** everything will still work.  But OP_Column is measurably faster
    ** by skipping the subsequent conditional, which is always true.
    */
    assert( pC->nHdrParsed<=p2 );         /* Conditional skipped */
    goto op_column_read_header;
  }

  /* Make sure at least the first p2+1 entries of the header have been
  ** parsed and valid information is in aOffset[] and pC->aType[].
  */
  if( pC->nHdrParsed<=p2 ){
    /* If there is more header available for parsing in the record, try
    ** to extract additional fields up through the p2+1-th field 
    */
    op_column_read_header:
    if( pC->iHdrOffset<aOffset[0] ){
      /* Make sure zData points to enough of the record to cover the header. */
      if( pC->aRow==0 ){
        memset(&sMem, 0, sizeof(sMem));
        rc = sqlite3VdbeMemFromBtree(pCrsr, 0, aOffset[0], 
                                     !pC->isTable, &sMem);
        if( rc!=SQLITE_OK ){