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Comment:Demonstration code on a possible technique for optimizing the use of IN operator on columns to the right of multicolumn indexes. If the OP_Noop generated where were really a new opcode that checked to see if there existed any entries in the index with a matching prefix, it might prevent unnecessary iterations of the IN operator.
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SHA3-256: 92f0fe155d5546fc7f4a443d0630613dabe149061966308e5420fad652278f16
User & Date: drh 2018-05-30 00:54:23
Context
2018-06-04
13:27
Merge recent changes from trunk. check-in: f8df2a8e user: drh tags: multikey-opt-idea
2018-05-30
00:54
Demonstration code on a possible technique for optimizing the use of IN operator on columns to the right of multicolumn indexes. If the OP_Noop generated where were really a new opcode that checked to see if there existed any entries in the index with a matching prefix, it might prevent unnecessary iterations of the IN operator. check-in: 92f0fe15 user: drh tags: multikey-opt-idea
2018-05-29
19:12
Increase the number of database handles opened by test script oserror.test to provoke an "out of file-descriptors" error to 20000 (from 2000). check-in: 3b00f734 user: dan tags: trunk
Changes
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Changes to src/where.c.

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    if( pLoop->wsFlags & WHERE_IN_ABLE && pLevel->u.in.nIn>0 ){
      struct InLoop *pIn;
      int j;
      sqlite3VdbeResolveLabel(v, pLevel->addrNxt);
      for(j=pLevel->u.in.nIn, pIn=&pLevel->u.in.aInLoop[j-1]; j>0; j--, pIn--){
        sqlite3VdbeJumpHere(v, pIn->addrInTop+1);
        if( pIn->eEndLoopOp!=OP_Noop ){




          sqlite3VdbeAddOp2(v, pIn->eEndLoopOp, pIn->iCur, pIn->addrInTop);
          VdbeCoverage(v);
          VdbeCoverageIf(v, pIn->eEndLoopOp==OP_PrevIfOpen);
          VdbeCoverageIf(v, pIn->eEndLoopOp==OP_NextIfOpen);
        }
        sqlite3VdbeJumpHere(v, pIn->addrInTop-1);
      }







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    if( pLoop->wsFlags & WHERE_IN_ABLE && pLevel->u.in.nIn>0 ){
      struct InLoop *pIn;
      int j;
      sqlite3VdbeResolveLabel(v, pLevel->addrNxt);
      for(j=pLevel->u.in.nIn, pIn=&pLevel->u.in.aInLoop[j-1]; j>0; j--, pIn--){
        sqlite3VdbeJumpHere(v, pIn->addrInTop+1);
        if( pIn->eEndLoopOp!=OP_Noop ){
          if( pIn->nPrefix ){
            sqlite3VdbeAddOp3(v, OP_Noop, pLevel->iIdxCur,
                              pIn->iBase, pIn->nPrefix);
          }
          sqlite3VdbeAddOp2(v, pIn->eEndLoopOp, pIn->iCur, pIn->addrInTop);
          VdbeCoverage(v);
          VdbeCoverageIf(v, pIn->eEndLoopOp==OP_PrevIfOpen);
          VdbeCoverageIf(v, pIn->eEndLoopOp==OP_NextIfOpen);
        }
        sqlite3VdbeJumpHere(v, pIn->addrInTop-1);
      }

Changes to src/whereInt.h.

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  int p1, p2;           /* Operands of the opcode used to ends the loop */
  union {               /* Information that depends on pWLoop->wsFlags */
    struct {
      int nIn;              /* Number of entries in aInLoop[] */
      struct InLoop {
        int iCur;              /* The VDBE cursor used by this IN operator */
        int addrInTop;         /* Top of the IN loop */


        u8 eEndLoopOp;         /* IN Loop terminator. OP_Next or OP_Prev */
      } *aInLoop;           /* Information about each nested IN operator */
    } in;                 /* Used when pWLoop->wsFlags&WHERE_IN_ABLE */
    Index *pCovidx;       /* Possible covering index for WHERE_MULTI_OR */
  } u;
  struct WhereLoop *pWLoop;  /* The selected WhereLoop object */
  Bitmask notReady;          /* FROM entries not usable at this level */







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  int p1, p2;           /* Operands of the opcode used to ends the loop */
  union {               /* Information that depends on pWLoop->wsFlags */
    struct {
      int nIn;              /* Number of entries in aInLoop[] */
      struct InLoop {
        int iCur;              /* The VDBE cursor used by this IN operator */
        int addrInTop;         /* Top of the IN loop */
        int iBase;             /* Base register of multi-key index record */
        int nPrefix;           /* Number of prior entires in the key */
        u8 eEndLoopOp;         /* IN Loop terminator. OP_Next or OP_Prev */
      } *aInLoop;           /* Information about each nested IN operator */
    } in;                 /* Used when pWLoop->wsFlags&WHERE_IN_ABLE */
    Index *pCovidx;       /* Possible covering index for WHERE_MULTI_OR */
  } u;
  struct WhereLoop *pWLoop;  /* The selected WhereLoop object */
  Bitmask notReady;          /* FROM entries not usable at this level */

Changes to src/wherecode.c.

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            int iCol = aiMap ? aiMap[iMap++] : 0;
            pIn->addrInTop = sqlite3VdbeAddOp3(v,OP_Column,iTab, iCol, iOut);
          }
          sqlite3VdbeAddOp1(v, OP_IsNull, iOut); VdbeCoverage(v);
          if( i==iEq ){
            pIn->iCur = iTab;
            pIn->eEndLoopOp = bRev ? OP_PrevIfOpen : OP_NextIfOpen;


          }else{
            pIn->eEndLoopOp = OP_Noop;
          }
          pIn++;
        }
      }
    }else{







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            int iCol = aiMap ? aiMap[iMap++] : 0;
            pIn->addrInTop = sqlite3VdbeAddOp3(v,OP_Column,iTab, iCol, iOut);
          }
          sqlite3VdbeAddOp1(v, OP_IsNull, iOut); VdbeCoverage(v);
          if( i==iEq ){
            pIn->iCur = iTab;
            pIn->eEndLoopOp = bRev ? OP_PrevIfOpen : OP_NextIfOpen;
            pIn->iBase = iReg - i;
            pIn->nPrefix = i;
          }else{
            pIn->eEndLoopOp = OP_Noop;
          }
          pIn++;
        }
      }
    }else{