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Overview
| Comment: | Invert the meaning of the regBignull flag so that it is 1 when doing the normal scan and 1 when scanning nulls. This enables the re-do jump at the bottom of the loop to be coded with a single OP_IfNotZero opcode, rather than a sequence of OP_If, OP_Integer, OP_Goto. |
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| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | descendants | both | nulls-last |
| Files: | files | file ages | folders |
| SHA3-256: |
bf875e1a259a4167694e06349458452d |
| User & Date: | drh 2019-08-23 13:32:03 |
Context
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2019-08-23
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| 16:12 | Simplification of the WHERE loop code generator for NULLS LAST saves a few CPU cycles and about a hundred bytes of code space. (check-in: e3ed2f49 user: drh tags: nulls-last) | |
| 13:32 | Invert the meaning of the regBignull flag so that it is 1 when doing the normal scan and 1 when scanning nulls. This enables the re-do jump at the bottom of the loop to be coded with a single OP_IfNotZero opcode, rather than a sequence of OP_If, OP_Integer, OP_Goto. (check-in: bf875e1a user: drh tags: nulls-last) | |
| 13:08 | Extra VDBE comments in the NULLS LAST logic provide landmarks to help understand the EXPLAIN output. (check-in: 649b08ea user: drh tags: nulls-last) | |
Changes
Changes to src/where.c.
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sqlite3VdbeChangeP5(v, pLevel->p5);
VdbeCoverage(v);
VdbeCoverageIf(v, pLevel->op==OP_Next);
VdbeCoverageIf(v, pLevel->op==OP_Prev);
VdbeCoverageIf(v, pLevel->op==OP_VNext);
if( pLevel->regBignull ){
sqlite3VdbeResolveLabel(v, pLevel->addrBignull);
addr = sqlite3VdbeAddOp1(v, OP_If, pLevel->regBignull);
VdbeComment((v, "If NULL-scan done"));
VdbeCoverage(v);
sqlite3VdbeAddOp2(v, OP_Integer, 1, pLevel->regBignull);
sqlite3VdbeAddOp2(v, OP_Goto, 0, pLevel->p2-1);
VdbeComment((v, "Do the NULL-scan"));
sqlite3VdbeJumpHere(v, addr);
}
#ifndef SQLITE_DISABLE_SKIPAHEAD_DISTINCT
if( addrSeek ) sqlite3VdbeJumpHere(v, addrSeek);
#endif
}else{
sqlite3VdbeResolveLabel(v, pLevel->addrCont);
}
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sqlite3VdbeChangeP5(v, pLevel->p5);
VdbeCoverage(v);
VdbeCoverageIf(v, pLevel->op==OP_Next);
VdbeCoverageIf(v, pLevel->op==OP_Prev);
VdbeCoverageIf(v, pLevel->op==OP_VNext);
if( pLevel->regBignull ){
sqlite3VdbeResolveLabel(v, pLevel->addrBignull);
sqlite3VdbeAddOp2(v, OP_IfNotZero, pLevel->regBignull, pLevel->p2-1);
}
#ifndef SQLITE_DISABLE_SKIPAHEAD_DISTINCT
if( addrSeek ) sqlite3VdbeJumpHere(v, addrSeek);
#endif
}else{
sqlite3VdbeResolveLabel(v, pLevel->addrCont);
}
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Changes to src/whereInt.h.
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int iIdxCur; /* The VDBE cursor used to access pIdx */
int addrBrk; /* Jump here to break out of the loop */
int addrNxt; /* Jump here to start the next IN combination */
int addrSkip; /* Jump here for next iteration of skip-scan */
int addrCont; /* Jump here to continue with the next loop cycle */
int addrFirst; /* First instruction of interior of the loop */
int addrBody; /* Beginning of the body of this loop */
int regBignull; /* big-null flag reg. True if NULLs not yet scanned */
int addrBignull; /* Jump here for next part of big-null scan */
#ifndef SQLITE_LIKE_DOESNT_MATCH_BLOBS
u32 iLikeRepCntr; /* LIKE range processing counter register (times 2) */
int addrLikeRep; /* LIKE range processing address */
#endif
u8 iFrom; /* Which entry in the FROM clause */
u8 op, p3, p5; /* Opcode, P3 & P5 of the opcode that ends the loop */
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int iIdxCur; /* The VDBE cursor used to access pIdx */ int addrBrk; /* Jump here to break out of the loop */ int addrNxt; /* Jump here to start the next IN combination */ int addrSkip; /* Jump here for next iteration of skip-scan */ int addrCont; /* Jump here to continue with the next loop cycle */ int addrFirst; /* First instruction of interior of the loop */ int addrBody; /* Beginning of the body of this loop */ int regBignull; /* big-null flag reg. True if a NULL-scan is needed */ int addrBignull; /* Jump here for next part of big-null scan */ #ifndef SQLITE_LIKE_DOESNT_MATCH_BLOBS u32 iLikeRepCntr; /* LIKE range processing counter register (times 2) */ int addrLikeRep; /* LIKE range processing address */ #endif u8 iFrom; /* Which entry in the FROM clause */ u8 op, p3, p5; /* Opcode, P3 & P5 of the opcode that ends the loop */ |
Changes to src/wherecode.c.
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** above has already left the cursor sitting on the correct row,
** so no further seeking is needed */
}else{
if( pLoop->wsFlags & WHERE_IN_EARLYOUT ){
sqlite3VdbeAddOp1(v, OP_SeekHit, iIdxCur);
}
if( regBignull ){
sqlite3VdbeAddOp2(v, OP_Integer, 0, regBignull);
VdbeComment((v, "NULL-scan flag"));
}
op = aStartOp[(start_constraints<<2) + (startEq<<1) + bRev];
assert( op!=0 );
sqlite3VdbeAddOp4Int(v, op, iIdxCur, addrNxt, regBase, nConstraint);
VdbeCoverage(v);
VdbeCoverageIf(v, op==OP_Rewind); testcase( op==OP_Rewind );
................................................................................
/* Top of the loop body */
pLevel->p2 = sqlite3VdbeCurrentAddr(v);
/* Check if the index cursor is past the end of the range. */
if( nConstraint ){
if( regBignull ){
sqlite3VdbeAddOp2(v, OP_If, regBignull, sqlite3VdbeCurrentAddr(v)+3);
VdbeComment((v, "If in NULL-scan"));
VdbeCoverage(v);
}
op = aEndOp[bRev*2 + endEq];
sqlite3VdbeAddOp4Int(v, op, iIdxCur, addrNxt, regBase, nConstraint);
testcase( op==OP_IdxGT ); VdbeCoverageIf(v, op==OP_IdxGT );
testcase( op==OP_IdxGE ); VdbeCoverageIf(v, op==OP_IdxGE );
testcase( op==OP_IdxLT ); VdbeCoverageIf(v, op==OP_IdxLT );
testcase( op==OP_IdxLE ); VdbeCoverageIf(v, op==OP_IdxLE );
}
if( regBignull ){
sqlite3VdbeAddOp2(v, OP_IfNot, regBignull, sqlite3VdbeCurrentAddr(v)+2);
VdbeComment((v, "If not in NULL-scan"));
VdbeCoverage(v);
if( bStopAtNull ){
op = aEndOp[bRev*2 + 0];
assert( op==OP_IdxGE || op==OP_IdxLE );
sqlite3VdbeAddOp4Int(v, op, iIdxCur, addrNxt, regBase, nConstraint);
testcase( op==OP_IdxGE ); VdbeCoverageIf(v, op==OP_IdxGE );
testcase( op==OP_IdxLE ); VdbeCoverageIf(v, op==OP_IdxLE );
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** above has already left the cursor sitting on the correct row,
** so no further seeking is needed */
}else{
if( pLoop->wsFlags & WHERE_IN_EARLYOUT ){
sqlite3VdbeAddOp1(v, OP_SeekHit, iIdxCur);
}
if( regBignull ){
sqlite3VdbeAddOp2(v, OP_Integer, 1, regBignull);
VdbeComment((v, "NULL-scan needed flag"));
}
op = aStartOp[(start_constraints<<2) + (startEq<<1) + bRev];
assert( op!=0 );
sqlite3VdbeAddOp4Int(v, op, iIdxCur, addrNxt, regBase, nConstraint);
VdbeCoverage(v);
VdbeCoverageIf(v, op==OP_Rewind); testcase( op==OP_Rewind );
................................................................................
/* Top of the loop body */
pLevel->p2 = sqlite3VdbeCurrentAddr(v);
/* Check if the index cursor is past the end of the range. */
if( nConstraint ){
if( regBignull ){
sqlite3VdbeAddOp2(v, OP_IfNot, regBignull, sqlite3VdbeCurrentAddr(v)+3);
VdbeComment((v, "If NULL-scan active"));
VdbeCoverage(v);
}
op = aEndOp[bRev*2 + endEq];
sqlite3VdbeAddOp4Int(v, op, iIdxCur, addrNxt, regBase, nConstraint);
testcase( op==OP_IdxGT ); VdbeCoverageIf(v, op==OP_IdxGT );
testcase( op==OP_IdxGE ); VdbeCoverageIf(v, op==OP_IdxGE );
testcase( op==OP_IdxLT ); VdbeCoverageIf(v, op==OP_IdxLT );
testcase( op==OP_IdxLE ); VdbeCoverageIf(v, op==OP_IdxLE );
}
if( regBignull ){
sqlite3VdbeAddOp2(v, OP_If, regBignull, sqlite3VdbeCurrentAddr(v)+2);
VdbeComment((v, "If NULL-scan pending"));
VdbeCoverage(v);
if( bStopAtNull ){
op = aEndOp[bRev*2 + 0];
assert( op==OP_IdxGE || op==OP_IdxLE );
sqlite3VdbeAddOp4Int(v, op, iIdxCur, addrNxt, regBase, nConstraint);
testcase( op==OP_IdxGE ); VdbeCoverageIf(v, op==OP_IdxGE );
testcase( op==OP_IdxLE ); VdbeCoverageIf(v, op==OP_IdxLE );
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