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Overview
Comment:Performance optimization on the Column opcode.
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SHA1: ecc98bef43c2fd07d64e4efddf340929a875ebac
User & Date: drh 2016-01-11 18:05:00.482
Context
2016-01-11
22:43
Fix duplicate test number in 'waloverwrite'. (check-in: f5fb826866 user: mistachkin tags: trunk)
18:30
Merge trunk with this branch. (check-in: a73d245f2e user: dan tags: fts5-offsets)
18:05
Performance optimization on the Column opcode. (check-in: ecc98bef43 user: drh tags: trunk)
14:19
Performance optimization in sqlite3WalkExpr(). (check-in: 2f8bd5fab8 user: drh tags: trunk)
Changes
Unified Diff Ignore Whitespace Patch
Changes to src/vdbe.c.
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  const u8 *zData;   /* Part of the record being decoded */
  const u8 *zHdr;    /* Next unparsed byte of the header */
  const u8 *zEndHdr; /* Pointer to first byte after the header */
  u32 offset;        /* Offset into the data */
  u64 offset64;      /* 64-bit offset */
  u32 avail;         /* Number of bytes of available data */
  u32 t;             /* A type code from the record header */
  u16 fx;            /* pDest->flags value */
  Mem *pReg;         /* PseudoTable input register */

  p2 = pOp->p2;
  assert( pOp->p3>0 && pOp->p3<=(p->nMem-p->nCursor) );
  pDest = &aMem[pOp->p3];
  memAboutToChange(p, pDest);
  assert( pOp->p1>=0 && pOp->p1<p->nCursor );








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  const u8 *zData;   /* Part of the record being decoded */
  const u8 *zHdr;    /* Next unparsed byte of the header */
  const u8 *zEndHdr; /* Pointer to first byte after the header */
  u32 offset;        /* Offset into the data */
  u64 offset64;      /* 64-bit offset */
  u32 avail;         /* Number of bytes of available data */
  u32 t;             /* A type code from the record header */

  Mem *pReg;         /* PseudoTable input register */

  p2 = pOp->p2;
  assert( pOp->p3>0 && pOp->p3<=(p->nMem-p->nCursor) );
  pDest = &aMem[pOp->p3];
  memAboutToChange(p, pDest);
  assert( pOp->p1>=0 && pOp->p1<p->nCursor );
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  ** all valid.
  */
  assert( p2<pC->nHdrParsed );
  assert( rc==SQLITE_OK );
  assert( sqlite3VdbeCheckMemInvariants(pDest) );
  if( VdbeMemDynamic(pDest) ) sqlite3VdbeMemSetNull(pDest);
  assert( t==pC->aType[p2] );

  if( pC->szRow>=aOffset[p2+1] ){
    /* This is the common case where the desired content fits on the original
    ** page - where the content is not on an overflow page */


    sqlite3VdbeSerialGet(pC->aRow+aOffset[p2], t, pDest);


















  }else{
    /* This branch happens only when content is on overflow pages */
    if( ((pOp->p5 & (OPFLAG_LENGTHARG|OPFLAG_TYPEOFARG))!=0
          && ((t>=12 && (t&1)==0) || (pOp->p5 & OPFLAG_TYPEOFARG)!=0))
     || (len = sqlite3VdbeSerialTypeLen(t))==0
    ){
      /* Content is irrelevant for
      **    1. the typeof() function,
      **    2. the length(X) function if X is a blob, and
      **    3. if the content length is zero.
      ** So we might as well use bogus content rather than reading
      ** content from disk.  NULL will work for the value for strings
      ** and blobs and whatever is in the payloadSize64 variable
      ** will work for everything else. */
      sqlite3VdbeSerialGet(t<=13 ? (u8*)&payloadSize64 : 0, t, pDest);
    }else{
      rc = sqlite3VdbeMemFromBtree(pCrsr, aOffset[p2], len, !pC->isTable,
                                   pDest);
      if( rc!=SQLITE_OK ){
        goto op_column_error;
      }
      sqlite3VdbeSerialGet((const u8*)pDest->z, t, pDest);
      pDest->flags &= ~MEM_Ephem;
    }
  }
  pDest->enc = encoding;

op_column_out:
  /* If the column value is an ephemeral string, go ahead and persist
  ** that string in case the cursor moves before the column value is
  ** used.  The following code does the equivalent of Deephemeralize()
  ** but does it faster. */
  if( (pDest->flags & MEM_Ephem)!=0 && pDest->z ){
    fx = pDest->flags & (MEM_Str|MEM_Blob);
    assert( fx!=0 );
    zData = (const u8*)pDest->z;
    len = pDest->n;
    if( sqlite3VdbeMemClearAndResize(pDest, len+2) ) goto no_mem;
    memcpy(pDest->z, zData, len);
    pDest->z[len] = 0;
    pDest->z[len+1] = 0;
    pDest->flags = fx|MEM_Term;
  }

op_column_error:
  UPDATE_MAX_BLOBSIZE(pDest);
  REGISTER_TRACE(pOp->p3, pDest);
  break;
}

/* Opcode: Affinity P1 P2 * P4 *








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  ** all valid.
  */
  assert( p2<pC->nHdrParsed );
  assert( rc==SQLITE_OK );
  assert( sqlite3VdbeCheckMemInvariants(pDest) );
  if( VdbeMemDynamic(pDest) ) sqlite3VdbeMemSetNull(pDest);
  assert( t==pC->aType[p2] );
  pDest->enc = encoding;
  if( pC->szRow>=aOffset[p2+1] ){
    /* This is the common case where the desired content fits on the original
    ** page - where the content is not on an overflow page */
    zData = pC->aRow + aOffset[p2];
    if( t<12 ){
      sqlite3VdbeSerialGet(zData, t, pDest);
    }else{
      /* If the column value is a string, we need a persistent value, not
      ** a MEM_Ephem value.  This branch is a fast short-cut that is equivalent
      ** to calling sqlite3VdbeSerialGet() and sqlite3VdbeDeephemeralize().
      */
      static const u16 aFlag[] = { MEM_Blob, MEM_Str|MEM_Term };
      pDest->n = len = (t-12)/2;
      if( pDest->szMalloc < len+2 ){
        pDest->flags = MEM_Null;
        if( sqlite3VdbeMemGrow(pDest, len+2, 0) ) goto no_mem;
      }else{
        pDest->z = pDest->zMalloc;
      }
      memcpy(pDest->z, zData, len);
      pDest->z[len] = 0;
      pDest->z[len+1] = 0;
      pDest->flags = aFlag[t&1];
    }
  }else{
    /* This branch happens only when content is on overflow pages */
    if( ((pOp->p5 & (OPFLAG_LENGTHARG|OPFLAG_TYPEOFARG))!=0
          && ((t>=12 && (t&1)==0) || (pOp->p5 & OPFLAG_TYPEOFARG)!=0))
     || (len = sqlite3VdbeSerialTypeLen(t))==0
    ){
      /* Content is irrelevant for
      **    1. the typeof() function,
      **    2. the length(X) function if X is a blob, and
      **    3. if the content length is zero.
      ** So we might as well use bogus content rather than reading
      ** content from disk. */
      static u8 aZero[8];  /* This is the bogus content */

      sqlite3VdbeSerialGet(aZero, t, pDest);
    }else{
      rc = sqlite3VdbeMemFromBtree(pCrsr, aOffset[p2], len, !pC->isTable,
                                   pDest);
      if( rc==SQLITE_OK ){


        sqlite3VdbeSerialGet((const u8*)pDest->z, t, pDest);
        pDest->flags &= ~MEM_Ephem;
      }
    }

  }
















op_column_out:
op_column_error:
  UPDATE_MAX_BLOBSIZE(pDest);
  REGISTER_TRACE(pOp->p3, pDest);
  break;
}

/* Opcode: Affinity P1 P2 * P4 *
︙︙