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Overview
Comment:Cause the ANALYZE command to build sqlite_stat1 table entries for empty tables with the assumption that such tables really contain 10 elements. This gives better query plans for tables that are truely empty, but is likely to cause problems in legacy systems, so the change is kept off trunk. Some TCL tests fail on this check-in due to the new stat1 entries.
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SHA3-256: c81f260c2d4791e40f74c86927a4e9efb79a9d241a66476e4af35c7bbe37a49c
User & Date: drh 2017-06-07 10:55:02
Context
2017-06-07
10:55
Cause the ANALYZE command to build sqlite_stat1 table entries for empty tables with the assumption that such tables really contain 10 elements. This gives better query plans for tables that are truely empty, but is likely to cause problems in legacy systems, so the change is kept off trunk. Some TCL tests fail on this check-in due to the new stat1 entries. Leaf check-in: c81f260c user: drh tags: analyze-empty-tables
2017-06-06
18:20
Add the SQLITE_DEFAULT_ROWEST compile-time option for changing the estimated number of rows in tables that lack sqlite_stat1 entries. check-in: 234ede26 user: drh tags: trunk
Changes
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Changes to src/analyze.c.

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    char *zRet = sqlite3MallocZero( (p->nKeyCol+1)*25 );
    if( zRet==0 ){
      sqlite3_result_error_nomem(context);
      return;
    }


    sqlite3_snprintf(24, zRet, "%llu", (u64)p->nRow);
    z = zRet + sqlite3Strlen30(zRet);
    for(i=0; i<p->nKeyCol; i++){
      u64 nDistinct = p->current.anDLt[i] + 1;
      u64 iVal = (p->nRow + nDistinct - 1) / nDistinct;
      sqlite3_snprintf(24, z, " %llu", iVal);
      z += sqlite3Strlen30(z);
      assert( p->current.anEq[i] );
    }
    assert( z[0]=='\0' && z>zRet );

    sqlite3_result_text(context, zRet, -1, sqlite3_free);
  }
#ifdef SQLITE_ENABLE_STAT3_OR_STAT4
  else if( eCall==STAT_GET_ROWID ){
................................................................................
){
  sqlite3 *db = pParse->db;    /* Database handle */
  Index *pIdx;                 /* An index to being analyzed */
  int iIdxCur;                 /* Cursor open on index being analyzed */
  int iTabCur;                 /* Table cursor */
  Vdbe *v;                     /* The virtual machine being built up */
  int i;                       /* Loop counter */
  int jZeroRows = -1;          /* Jump from here if number of rows is zero */
  int iDb;                     /* Index of database containing pTab */
  u8 needTableCnt = 1;         /* True to count the table */
  int regNewRowid = iMem++;    /* Rowid for the inserted record */
  int regStat4 = iMem++;       /* Register to hold Stat4Accum object */
  int regChng = iMem++;        /* Index of changed index field */
#ifdef SQLITE_ENABLE_STAT3_OR_STAT4
  int regRowid = iMem++;       /* Rowid argument passed to stat_push() */
................................................................................
    assert( regChng==(regStat4+1) );
    sqlite3VdbeAddOp4(v, OP_Function0, 1, regStat4, regTemp,
                     (char*)&statPushFuncdef, P4_FUNCDEF);
    sqlite3VdbeChangeP5(v, 2+IsStat34);
    sqlite3VdbeAddOp2(v, OP_Next, iIdxCur, addrNextRow); VdbeCoverage(v);

    /* Add the entry to the stat1 table. */

    callStatGet(v, regStat4, STAT_GET_STAT1, regStat1);
    assert( "BBB"[0]==SQLITE_AFF_TEXT );
    sqlite3VdbeAddOp4(v, OP_MakeRecord, regTabname, 3, regTemp, "BBB", 0);
    sqlite3VdbeAddOp2(v, OP_NewRowid, iStatCur, regNewRowid);
    sqlite3VdbeAddOp3(v, OP_Insert, iStatCur, regTemp, regNewRowid);
    sqlite3VdbeChangeP5(v, OPFLAG_APPEND);

................................................................................
      int regSampleRowid = regCol + nCol;
      int addrNext;
      int addrIsNull;
      u8 seekOp = HasRowid(pTab) ? OP_NotExists : OP_NotFound;

      pParse->nMem = MAX(pParse->nMem, regCol+nCol);



      addrNext = sqlite3VdbeCurrentAddr(v);
      callStatGet(v, regStat4, STAT_GET_ROWID, regSampleRowid);
      addrIsNull = sqlite3VdbeAddOp1(v, OP_IsNull, regSampleRowid);
      VdbeCoverage(v);
      callStatGet(v, regStat4, STAT_GET_NEQ, regEq);
      callStatGet(v, regStat4, STAT_GET_NLT, regLt);
      callStatGet(v, regStat4, STAT_GET_NDLT, regDLt);
................................................................................
      sqlite3VdbeAddOp3(v, OP_MakeRecord, regCol, nCol, regSample);
#endif
      sqlite3VdbeAddOp3(v, OP_MakeRecord, regTabname, 6, regTemp);
      sqlite3VdbeAddOp2(v, OP_NewRowid, iStatCur+1, regNewRowid);
      sqlite3VdbeAddOp3(v, OP_Insert, iStatCur+1, regTemp, regNewRowid);
      sqlite3VdbeAddOp2(v, OP_Goto, 1, addrNext); /* P1==1 for end-of-loop */
      sqlite3VdbeJumpHere(v, addrIsNull);

    }
#endif /* SQLITE_ENABLE_STAT3_OR_STAT4 */

    /* End of analysis */
    sqlite3VdbeJumpHere(v, addrRewind);
  }


  /* Create a single sqlite_stat1 entry containing NULL as the index
  ** name and the row count as the content.
  */
  if( pOnlyIdx==0 && needTableCnt ){
    VdbeComment((v, "%s", pTab->zName));
    sqlite3VdbeAddOp2(v, OP_Count, iTabCur, regStat1);
    jZeroRows = sqlite3VdbeAddOp1(v, OP_IfNot, regStat1); VdbeCoverage(v);
    sqlite3VdbeAddOp2(v, OP_Null, 0, regIdxname);
    assert( "BBB"[0]==SQLITE_AFF_TEXT );
    sqlite3VdbeAddOp4(v, OP_MakeRecord, regTabname, 3, regTemp, "BBB", 0);
    sqlite3VdbeAddOp2(v, OP_NewRowid, iStatCur, regNewRowid);
    sqlite3VdbeAddOp3(v, OP_Insert, iStatCur, regTemp, regNewRowid);
    sqlite3VdbeChangeP5(v, OPFLAG_APPEND);
    sqlite3VdbeJumpHere(v, jZeroRows);
  }
}


/*
** Generate code that will cause the most recent index analysis to
** be loaded into internal hash tables where is can be used.







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    char *zRet = sqlite3MallocZero( (p->nKeyCol+1)*25 );
    if( zRet==0 ){
      sqlite3_result_error_nomem(context);
      return;
    }

    /* Never let the estimated number of rows be less than 10 */
    sqlite3_snprintf(24, zRet, "%llu", MAX((u64)p->nRow, 10));
    z = zRet + sqlite3Strlen30(zRet);
    for(i=0; i<p->nKeyCol; i++){
      u64 nDistinct = p->current.anDLt[i] + 1;
      u64 iVal = (p->nRow + nDistinct - 1) / nDistinct;
      sqlite3_snprintf(24, z, " %llu", iVal);
      z += sqlite3Strlen30(z);

    }
    assert( z[0]=='\0' && z>zRet );

    sqlite3_result_text(context, zRet, -1, sqlite3_free);
  }
#ifdef SQLITE_ENABLE_STAT3_OR_STAT4
  else if( eCall==STAT_GET_ROWID ){
................................................................................
){
  sqlite3 *db = pParse->db;    /* Database handle */
  Index *pIdx;                 /* An index to being analyzed */
  int iIdxCur;                 /* Cursor open on index being analyzed */
  int iTabCur;                 /* Table cursor */
  Vdbe *v;                     /* The virtual machine being built up */
  int i;                       /* Loop counter */

  int iDb;                     /* Index of database containing pTab */
  u8 needTableCnt = 1;         /* True to count the table */
  int regNewRowid = iMem++;    /* Rowid for the inserted record */
  int regStat4 = iMem++;       /* Register to hold Stat4Accum object */
  int regChng = iMem++;        /* Index of changed index field */
#ifdef SQLITE_ENABLE_STAT3_OR_STAT4
  int regRowid = iMem++;       /* Rowid argument passed to stat_push() */
................................................................................
    assert( regChng==(regStat4+1) );
    sqlite3VdbeAddOp4(v, OP_Function0, 1, regStat4, regTemp,
                     (char*)&statPushFuncdef, P4_FUNCDEF);
    sqlite3VdbeChangeP5(v, 2+IsStat34);
    sqlite3VdbeAddOp2(v, OP_Next, iIdxCur, addrNextRow); VdbeCoverage(v);

    /* Add the entry to the stat1 table. */
    sqlite3VdbeJumpHere(v, addrRewind);
    callStatGet(v, regStat4, STAT_GET_STAT1, regStat1);
    assert( "BBB"[0]==SQLITE_AFF_TEXT );
    sqlite3VdbeAddOp4(v, OP_MakeRecord, regTabname, 3, regTemp, "BBB", 0);
    sqlite3VdbeAddOp2(v, OP_NewRowid, iStatCur, regNewRowid);
    sqlite3VdbeAddOp3(v, OP_Insert, iStatCur, regTemp, regNewRowid);
    sqlite3VdbeChangeP5(v, OPFLAG_APPEND);

................................................................................
      int regSampleRowid = regCol + nCol;
      int addrNext;
      int addrIsNull;
      u8 seekOp = HasRowid(pTab) ? OP_NotExists : OP_NotFound;

      pParse->nMem = MAX(pParse->nMem, regCol+nCol);

      addrRewind = sqlite3VdbeAddOp1(v, OP_Rewind, iIdxCur);
      VdbeCoverage(v);
      addrNext = sqlite3VdbeCurrentAddr(v);
      callStatGet(v, regStat4, STAT_GET_ROWID, regSampleRowid);
      addrIsNull = sqlite3VdbeAddOp1(v, OP_IsNull, regSampleRowid);
      VdbeCoverage(v);
      callStatGet(v, regStat4, STAT_GET_NEQ, regEq);
      callStatGet(v, regStat4, STAT_GET_NLT, regLt);
      callStatGet(v, regStat4, STAT_GET_NDLT, regDLt);
................................................................................
      sqlite3VdbeAddOp3(v, OP_MakeRecord, regCol, nCol, regSample);
#endif
      sqlite3VdbeAddOp3(v, OP_MakeRecord, regTabname, 6, regTemp);
      sqlite3VdbeAddOp2(v, OP_NewRowid, iStatCur+1, regNewRowid);
      sqlite3VdbeAddOp3(v, OP_Insert, iStatCur+1, regTemp, regNewRowid);
      sqlite3VdbeAddOp2(v, OP_Goto, 1, addrNext); /* P1==1 for end-of-loop */
      sqlite3VdbeJumpHere(v, addrIsNull);
      sqlite3VdbeJumpHere(v, addrRewind);
    }
#endif /* SQLITE_ENABLE_STAT3_OR_STAT4 */

    /* End of analysis */

  }


  /* Create a single sqlite_stat1 entry containing NULL as the index
  ** name and the row count as the content.
  */
  if( pOnlyIdx==0 && needTableCnt ){
    VdbeComment((v, "%s", pTab->zName));
    sqlite3VdbeAddOp2(v, OP_Count, iTabCur, regStat1);
    sqlite3VdbeAddOp2(v, OP_AddImm, regStat1, 10);
    sqlite3VdbeAddOp2(v, OP_Null, 0, regIdxname);
    assert( "BBB"[0]==SQLITE_AFF_TEXT );
    sqlite3VdbeAddOp4(v, OP_MakeRecord, regTabname, 3, regTemp, "BBB", 0);
    sqlite3VdbeAddOp2(v, OP_NewRowid, iStatCur, regNewRowid);
    sqlite3VdbeAddOp3(v, OP_Insert, iStatCur, regTemp, regNewRowid);
    sqlite3VdbeChangeP5(v, OPFLAG_APPEND);

  }
}


/*
** Generate code that will cause the most recent index analysis to
** be loaded into internal hash tables where is can be used.

Changes to test/analyze.test.

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    ANALYZE main.t1;
  }
} {0 {}}
do_test analyze-1.11 {
  execsql {
    SELECT * FROM sqlite_stat1
  }
} {}
do_test analyze-1.12 {
  catchsql {
    ANALYZE t1;
  }
} {0 {}}
do_test analyze-1.13 {
  execsql {
    SELECT * FROM sqlite_stat1
  }
} {}

# Create some indices that can be analyzed.  But do not yet add
# data.  Without data in the tables, no analysis is done.
#
do_test analyze-2.1 {
  execsql {
    CREATE INDEX t1i1 ON t1(a);
    ANALYZE main.t1;
    SELECT * FROM sqlite_stat1 ORDER BY idx;
  }
} {}
do_test analyze-2.2 {
  execsql {
    CREATE INDEX t1i2 ON t1(b);
    ANALYZE t1;
    SELECT * FROM sqlite_stat1 ORDER BY idx;
  }
} {}
do_test analyze-2.3 {
  execsql {
    CREATE INDEX t1i3 ON t1(a,b);
    ANALYZE main;
    SELECT * FROM sqlite_stat1 ORDER BY idx;
  }
} {}

# Start adding data to the table.  Verify that the analysis
# is done correctly.
#
do_test analyze-3.1 {
  execsql {
    INSERT INTO t1 VALUES(1,2);







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    ANALYZE main.t1;
  }
} {0 {}}
do_test analyze-1.11 {
  execsql {
    SELECT * FROM sqlite_stat1
  }
} {t1 {} 0}
do_test analyze-1.12 {
  catchsql {
    ANALYZE t1;
  }
} {0 {}}
do_test analyze-1.13 {
  execsql {
    SELECT * FROM sqlite_stat1
  }
} {t1 {} 0}

# Create some indices that can be analyzed. 
# Zero sqlite_stat1 entries are created.
#
do_test analyze-2.1 {
  execsql {
    CREATE INDEX t1i1 ON t1(a);
    ANALYZE main.t1;
    SELECT * FROM sqlite_stat1 ORDER BY idx;
  }
} {t1 t1i1 {0 0}}
do_test analyze-2.2 {
  execsql {
    CREATE INDEX t1i2 ON t1(b);
    ANALYZE t1;
    SELECT * FROM sqlite_stat1 ORDER BY idx;
  }
} {t1 t1i1 {0 0} t1 t1i2 {0 0}}
do_test analyze-2.3 {
  execsql {
    CREATE INDEX t1i3 ON t1(a,b);
    ANALYZE main;
    SELECT * FROM sqlite_stat1 ORDER BY idx;
  }
} {t1 t1i1 {0 0} t1 t1i2 {0 0} t1 t1i3 {0 0 0}}

# Start adding data to the table.  Verify that the analysis
# is done correctly.
#
do_test analyze-3.1 {
  execsql {
    INSERT INTO t1 VALUES(1,2);

Changes to test/analyze3.test.

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  CREATE TABLE t1(a,b,c);
  CREATE INDEX t1a ON t1(a);
  ANALYZE;
  SELECT * FROM sqlite_stat1;
  INSERT INTO sqlite_stat1(tbl,idx,stat) VALUES('t1','t1a','12000');
  INSERT INTO sqlite_stat1(tbl,idx,stat) VALUES('t1','t1a','12000');
  ANALYZE sqlite_master;
}

finish_test







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  CREATE TABLE t1(a,b,c);
  CREATE INDEX t1a ON t1(a);
  ANALYZE;
  SELECT * FROM sqlite_stat1;
  INSERT INTO sqlite_stat1(tbl,idx,stat) VALUES('t1','t1a','12000');
  INSERT INTO sqlite_stat1(tbl,idx,stat) VALUES('t1','t1a','12000');
  ANALYZE sqlite_master;
} {t1 t1a {0 0}}

finish_test