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Overview
Comment:Improvements to comments. Minor changes to code in the hot path of OP_Column - with the hope of get a few cycles of performance improvement.
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Timelines: family | ancestors | descendants | both | faster-typeof-and-length
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SHA1:ca093103437f141caa3eb11539c6eb7b4dd65175
User & Date: drh 2012-03-28 13:41:10
Context
2012-03-28
16:14
Minor changes to the core of OP_Column for performance and to clarify the critical path. Closed-Leaf check-in: 86839476 user: drh tags: faster-typeof-and-length
15:44
This change turned out to the code slower. Side track it. Was: Tweaks to the OP_Column opcode for clarity of presentation. Closed-Leaf check-in: 4d516240 user: drh tags: mistake
13:41
Improvements to comments. Minor changes to code in the hot path of OP_Column - with the hope of get a few cycles of performance improvement. check-in: ca093103 user: drh tags: faster-typeof-and-length
02:51
Test cases for length() of a large blob in an aggregate query. check-in: d095fa4b user: drh tags: faster-typeof-and-length
Changes
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Changes to src/vdbe.c.

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** the result.
**
** If the OPFLAG_CLEARCACHE bit is set on P5 and P1 is a pseudo-table cursor,
** then the cache of the cursor is reset prior to extracting the column.
** The first OP_Column against a pseudo-table after the value of the content
** register has changed should have this bit set.
**
** If the OPFLAG_LENGTHARG bit is set on P5 then the result is guaranteed
** to only be used as the argument of a length() or typeof() function and
** so loading of large blobs and strings can be skipped - all that is necessary
** is that the size and type information be set.
*/
case OP_Column: {
  u32 payloadSize;   /* Number of bytes in the record */
  i64 payloadSize64; /* Number of bytes in the record */
  int p1;            /* P1 value of the opcode */
  int p2;            /* column number to retrieve */
  VdbeCursor *pC;    /* The VDBE cursor */
................................................................................
      if( payloadSize <= (u32)avail ){
        zRec = zData;
        pC->aRow = (u8*)zData;
      }else{
        pC->aRow = 0;
      }
    }
    /* The following assert is true in all cases accept when
    ** the database file has been corrupted externally.
    **    assert( zRec!=0 || avail>=payloadSize || avail>=9 ); */
    szHdr = getVarint32((u8*)zData, offset);

    /* Make sure a corrupt database has not given us an oversize header.
    ** Do this now to avoid an oversize memory allocation.
    **
................................................................................
        szField = sqlite3VdbeSerialTypeLen(t);
        offset += szField;
        if( offset<szField ){  /* True if offset overflows */
          zIdx = &zEndHdr[1];  /* Forces SQLITE_CORRUPT return below */
          break;
        }
      }else{
        /* If i is less that nField, then there are less fields in this
        ** record than SetNumColumns indicated there are columns in the
        ** table. Set the offset for any extra columns not present in
        ** the record to 0. This tells code below to store a NULL
        ** instead of deserializing a value from the record.
        */
        aOffset[i] = 0;
      }
    }
    sqlite3VdbeMemRelease(&sMem);
    sMem.flags = MEM_Null;

................................................................................
  */
  if( aOffset[p2] ){
    assert( rc==SQLITE_OK );
    if( zRec ){
      VdbeMemRelease(pDest);
      sqlite3VdbeSerialGet((u8 *)&zRec[aOffset[p2]], aType[p2], pDest);
    }else{

      len = sqlite3VdbeSerialTypeLen(aType[p2]);
      if( (pOp->p5 & (OPFLAG_LENGTHARG|OPFLAG_TYPEOFARG))!=0
       && (((t = aType[p2])>=12 && (t&1)==0) || (pOp->p5 & OPFLAG_TYPEOFARG)!=0)
      ){
        /* Content is irrelevant for the typeof() function and for
        ** the length(x) function is x is a blob.  So we might as well use
        ** bogus content rather than reading content from disk.  NULL works
        ** for text and blob and whatever is in the payloadSize64 variable
        ** will work for everything else. */
        zData = t<12 ? (char*)&payloadSize64 : 0;
      }else{
        sqlite3VdbeMemMove(&sMem, pDest);
        rc = sqlite3VdbeMemFromBtree(pCrsr, aOffset[p2], len,  pC->isIndex,
                                     &sMem);
        if( rc!=SQLITE_OK ){
          goto op_column_out;
        }
        zData = sMem.z;
      }
      sqlite3VdbeSerialGet((u8*)zData, aType[p2], pDest);
    }
    pDest->enc = encoding;
  }else{
    if( pOp->p4type==P4_MEM ){
      sqlite3VdbeMemShallowCopy(pDest, pOp->p4.pMem, MEM_Static);
    }else{
      MemSetTypeFlag(pDest, MEM_Null);







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** the result.
**
** If the OPFLAG_CLEARCACHE bit is set on P5 and P1 is a pseudo-table cursor,
** then the cache of the cursor is reset prior to extracting the column.
** The first OP_Column against a pseudo-table after the value of the content
** register has changed should have this bit set.
**
** If the OPFLAG_LENGTHARG and OPFLAG_TYPEOFARG bits are set on P5 when
** the result is guaranteed to only be used as the argument of a length()
** or typeof() function, respectively.  The loading of large blobs can be
** skipped for length() and all content loading can be skipped for typeof().
*/
case OP_Column: {
  u32 payloadSize;   /* Number of bytes in the record */
  i64 payloadSize64; /* Number of bytes in the record */
  int p1;            /* P1 value of the opcode */
  int p2;            /* column number to retrieve */
  VdbeCursor *pC;    /* The VDBE cursor */
................................................................................
      if( payloadSize <= (u32)avail ){
        zRec = zData;
        pC->aRow = (u8*)zData;
      }else{
        pC->aRow = 0;
      }
    }
    /* The following assert is true in all cases except when
    ** the database file has been corrupted externally.
    **    assert( zRec!=0 || avail>=payloadSize || avail>=9 ); */
    szHdr = getVarint32((u8*)zData, offset);

    /* Make sure a corrupt database has not given us an oversize header.
    ** Do this now to avoid an oversize memory allocation.
    **
................................................................................
        szField = sqlite3VdbeSerialTypeLen(t);
        offset += szField;
        if( offset<szField ){  /* True if offset overflows */
          zIdx = &zEndHdr[1];  /* Forces SQLITE_CORRUPT return below */
          break;
        }
      }else{
        /* If i is less that nField, then there are fewer fields in this
        ** record than SetNumColumns indicated there are columns in the
        ** table. Set the offset for any extra columns not present in
        ** the record to 0. This tells code below to store the default value
        ** for the column instead of deserializing a value from the record.
        */
        aOffset[i] = 0;
      }
    }
    sqlite3VdbeMemRelease(&sMem);
    sMem.flags = MEM_Null;

................................................................................
  */
  if( aOffset[p2] ){
    assert( rc==SQLITE_OK );
    if( zRec ){
      VdbeMemRelease(pDest);
      sqlite3VdbeSerialGet((u8 *)&zRec[aOffset[p2]], aType[p2], pDest);
    }else{
      t = aType[p2];
      len = sqlite3VdbeSerialTypeLen(t);
      if( (pOp->p5 & (OPFLAG_LENGTHARG|OPFLAG_TYPEOFARG))!=0
       && ((t>=12 && (t&1)==0) || (pOp->p5 & OPFLAG_TYPEOFARG)!=0)
      ){
        /* Content is irrelevant for the typeof() function and for
        ** the length(X) function if X is a blob.  So we might as well use
        ** bogus content rather than reading content from disk.  NULL works
        ** for text and blob and whatever is in the payloadSize64 variable
        ** will work for everything else. */
        zData = t<12 ? (char*)&payloadSize64 : 0;
      }else{
        sqlite3VdbeMemMove(&sMem, pDest);
        rc = sqlite3VdbeMemFromBtree(pCrsr, aOffset[p2], len,  pC->isIndex,
                                     &sMem);
        if( rc!=SQLITE_OK ){
          goto op_column_out;
        }
        zData = sMem.z;
      }
      sqlite3VdbeSerialGet((u8*)zData, t, pDest);
    }
    pDest->enc = encoding;
  }else{
    if( pOp->p4type==P4_MEM ){
      sqlite3VdbeMemShallowCopy(pDest, pOp->p4.pMem, MEM_Static);
    }else{
      MemSetTypeFlag(pDest, MEM_Null);