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Overview
Comment:Enhancements to skip-scan such that it is operable when a middle column of an index is skipped while the left-most column is constrained in the WHERE clause.
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SHA1:bc985caa7816f1f873ad8e4467c5278399f315ce
User & Date: drh 2014-08-20 23:38:07
Context
2014-08-20
23:42
Increase the version number to 3.8.7 check-in: 91594aae user: drh tags: trunk
23:38
Enhancements to skip-scan such that it is operable when a middle column of an index is skipped while the left-most column is constrained in the WHERE clause. check-in: bc985caa user: drh tags: trunk
18:43
A small performance improvement in freeSpace() by special-casing the relatively common case of an empty freelist. check-in: 49f44d35 user: drh tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/where.c.

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  struct SrcList_item *pItem = pWInfo->pTabList->a + p->iTab;
  Table *pTab = pItem->pTab;
  sqlite3DebugPrintf("%c%2d.%0*llx.%0*llx", p->cId,
                     p->iTab, nb, p->maskSelf, nb, p->prereq);
  sqlite3DebugPrintf(" %12s",
                     pItem->zAlias ? pItem->zAlias : pTab->zName);
  if( (p->wsFlags & WHERE_VIRTUALTABLE)==0 ){
     const char *zName;
     if( p->u.btree.pIndex && (zName = p->u.btree.pIndex->zName)!=0 ){
      if( strncmp(zName, "sqlite_autoindex_", 17)==0 ){
        int i = sqlite3Strlen30(zName) - 1;
        while( zName[i]!='_' ) i--;
        zName += i;
      }
      sqlite3DebugPrintf(".%-16s %2d", zName, p->u.btree.nEq);
    }else{
................................................................................
                p->u.vtab.idxNum, p->u.vtab.idxStr, p->u.vtab.omitMask);
    }else{
      z = sqlite3_mprintf("(%d,%x)", p->u.vtab.idxNum, p->u.vtab.omitMask);
    }
    sqlite3DebugPrintf(" %-19s", z);
    sqlite3_free(z);
  }



  sqlite3DebugPrintf(" f %05x N %d", p->wsFlags, p->nLTerm);

  sqlite3DebugPrintf(" cost %d,%d,%d\n", p->rSetup, p->rRun, p->nOut);
#ifdef SQLITE_ENABLE_TREE_EXPLAIN
  /* If the 0x100 bit of wheretracing is set, then show all of the constraint
  ** expressions in the WhereLoop.aLTerm[] array.
  */
  if( p->nLTerm && (sqlite3WhereTrace & 0x100)!=0 ){  /* WHERETRACE 0x100 */
    int i;
................................................................................
  ** The magic number 18 is selected on the basis that scanning 17 rows
  ** is almost always quicker than an index seek (even though if the index
  ** contains fewer than 2^17 rows we assume otherwise in other parts of
  ** the code). And, even if it is not, it should not be too much slower. 
  ** On the other hand, the extra seeks could end up being significantly
  ** more expensive.  */
  assert( 42==sqlite3LogEst(18) );
  if( pTerm==0
   && saved_nEq==saved_nSkip
   && saved_nEq+1<pProbe->nKeyCol
   && pProbe->aiRowLogEst[saved_nEq+1]>=42  /* TUNING: Minimum for skip-scan */
   && (rc = whereLoopResize(db, pNew, pNew->nLTerm+1))==SQLITE_OK
  ){
    LogEst nIter;
    pNew->u.btree.nEq++;
    pNew->u.btree.nSkip++;
    pNew->aLTerm[pNew->nLTerm++] = 0;
    pNew->wsFlags |= WHERE_SKIPSCAN;
    nIter = pProbe->aiRowLogEst[saved_nEq] - pProbe->aiRowLogEst[saved_nEq+1];






    pNew->nOut -= nIter;
    whereLoopAddBtreeIndex(pBuilder, pSrc, pProbe, nIter + nInMul);
    pNew->nOut = saved_nOut;


  }
  for(; rc==SQLITE_OK && pTerm!=0; pTerm = whereScanNext(&scan)){
    u16 eOp = pTerm->eOperator;   /* Shorthand for pTerm->eOperator */
    LogEst rCostIdx;
    LogEst nOutUnadjusted;        /* nOut before IN() and WHERE adjustments */
    int nIn = 0;
#ifdef SQLITE_ENABLE_STAT3_OR_STAT4







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  struct SrcList_item *pItem = pWInfo->pTabList->a + p->iTab;
  Table *pTab = pItem->pTab;
  sqlite3DebugPrintf("%c%2d.%0*llx.%0*llx", p->cId,
                     p->iTab, nb, p->maskSelf, nb, p->prereq);
  sqlite3DebugPrintf(" %12s",
                     pItem->zAlias ? pItem->zAlias : pTab->zName);
  if( (p->wsFlags & WHERE_VIRTUALTABLE)==0 ){
    const char *zName;
    if( p->u.btree.pIndex && (zName = p->u.btree.pIndex->zName)!=0 ){
      if( strncmp(zName, "sqlite_autoindex_", 17)==0 ){
        int i = sqlite3Strlen30(zName) - 1;
        while( zName[i]!='_' ) i--;
        zName += i;
      }
      sqlite3DebugPrintf(".%-16s %2d", zName, p->u.btree.nEq);
    }else{
................................................................................
                p->u.vtab.idxNum, p->u.vtab.idxStr, p->u.vtab.omitMask);
    }else{
      z = sqlite3_mprintf("(%d,%x)", p->u.vtab.idxNum, p->u.vtab.omitMask);
    }
    sqlite3DebugPrintf(" %-19s", z);
    sqlite3_free(z);
  }
  if( p->wsFlags & WHERE_SKIPSCAN ){
    sqlite3DebugPrintf(" f %05x %d-%d", p->wsFlags, p->nLTerm,p->u.btree.nSkip);
  }else{
    sqlite3DebugPrintf(" f %05x N %d", p->wsFlags, p->nLTerm);
  }
  sqlite3DebugPrintf(" cost %d,%d,%d\n", p->rSetup, p->rRun, p->nOut);
#ifdef SQLITE_ENABLE_TREE_EXPLAIN
  /* If the 0x100 bit of wheretracing is set, then show all of the constraint
  ** expressions in the WhereLoop.aLTerm[] array.
  */
  if( p->nLTerm && (sqlite3WhereTrace & 0x100)!=0 ){  /* WHERETRACE 0x100 */
    int i;
................................................................................
  ** The magic number 18 is selected on the basis that scanning 17 rows
  ** is almost always quicker than an index seek (even though if the index
  ** contains fewer than 2^17 rows we assume otherwise in other parts of
  ** the code). And, even if it is not, it should not be too much slower. 
  ** On the other hand, the extra seeks could end up being significantly
  ** more expensive.  */
  assert( 42==sqlite3LogEst(18) );

  if( saved_nEq==saved_nSkip
   && saved_nEq+1<pProbe->nKeyCol
   && pProbe->aiRowLogEst[saved_nEq+1]>=42  /* TUNING: Minimum for skip-scan */
   && (rc = whereLoopResize(db, pNew, pNew->nLTerm+1))==SQLITE_OK
  ){
    LogEst nIter;
    pNew->u.btree.nEq++;
    pNew->u.btree.nSkip++;
    pNew->aLTerm[pNew->nLTerm++] = 0;
    pNew->wsFlags |= WHERE_SKIPSCAN;
    nIter = pProbe->aiRowLogEst[saved_nEq] - pProbe->aiRowLogEst[saved_nEq+1];
    if( pTerm ){
      /* TUNING:  When estimating skip-scan for a term that is also indexable,
      ** increase the cost of the skip-scan by 2x, to make it a little less
      ** desirable than the regular index lookup. */
      nIter += 10;  assert( 10==sqlite3LogEst(2) );
    }
    pNew->nOut -= nIter;
    whereLoopAddBtreeIndex(pBuilder, pSrc, pProbe, nIter + nInMul);
    pNew->nOut = saved_nOut;
    pNew->u.btree.nEq = saved_nEq;
    pNew->u.btree.nSkip = saved_nSkip;
  }
  for(; rc==SQLITE_OK && pTerm!=0; pTerm = whereScanNext(&scan)){
    u16 eOp = pTerm->eOperator;   /* Shorthand for pTerm->eOperator */
    LogEst rCostIdx;
    LogEst nOutUnadjusted;        /* nOut before IN() and WHERE adjustments */
    int nIn = 0;
#ifdef SQLITE_ENABLE_STAT3_OR_STAT4

Added test/skipscan3.test.



















































































































































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# 2014-08-20
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
#
# This file implements tests of the "skip-scan" query strategy.
# In particular, this file looks at skipping intermediate terms
# in an index.  For example, if (a,b,c) are indexed, and we have
# "WHERE a=?1 AND c=?2" - verify that skip-scan can still be used.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl

do_execsql_test skipscan3-1.1 {
  CREATE TABLE t1(a,b,c,d,PRIMARY KEY(a,b,c));
  WITH RECURSIVE
    c(x) AS (VALUES(1) UNION ALL SELECT x+1 FROM c WHERE x<1000)
  INSERT INTO t1(a,b,c,d)
    SELECT 1, 1, x, printf('x%04d',x) FROM c;
  ANALYZE;
} {}

# This version has long used skip-scan because of the "+a"
#
do_execsql_test skipscan3-1.2eqp {
  EXPLAIN QUERY PLAN SELECT d FROM t1 WHERE +a=1 AND c=32;
} {/*ANY(a) AND ANY(b)*/}
do_execsql_test skipscan3-1.2 {
  SELECT d FROM t1 WHERE +a=1 AND c=32;
} {x0032}

# This version (with "a" instead of "+a") should use skip-scan but
# did not prior to changes implemented on 2014-08-20
#
do_execsql_test skipscan3-1.3eqp {
  EXPLAIN QUERY PLAN SELECT d FROM t1 WHERE a=1 AND c=32;
} {/*ANY(a) AND ANY(b)*/}
do_execsql_test skipscan3-1.3 {
  SELECT d FROM t1 WHERE a=1 AND c=32;
} {x0032}

# Repeat the test on a WITHOUT ROWID table
#
do_execsql_test skipscan3-2.1 {
  CREATE TABLE t2(a,b,c,d,PRIMARY KEY(a,b,c)) WITHOUT ROWID;
  WITH RECURSIVE
    c(x) AS (VALUES(1) UNION ALL SELECT x+1 FROM c WHERE x<1000)
  INSERT INTO t2(a,b,c,d)
    SELECT 1, 1, x, printf('x%04d',x) FROM c;
  ANALYZE;
} {}
do_execsql_test skipscan3-2.2eqp {
  EXPLAIN QUERY PLAN SELECT d FROM t2 WHERE +a=1 AND c=32;
} {/*ANY(a) AND ANY(b)*/}
do_execsql_test skipscan3-2.2 {
  SELECT d FROM t2 WHERE +a=1 AND c=32;
} {x0032}
do_execsql_test skipscan3-2.3eqp {
  EXPLAIN QUERY PLAN SELECT d FROM t2 WHERE a=1 AND c=32;
} {/*ANY(a) AND ANY(b)*/}
do_execsql_test skipscan3-2.3 {
  SELECT d FROM t2 WHERE a=1 AND c=32;
} {x0032}

  
finish_test