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Overview
Comment:Allow an automatic index to be used if the only uses of declared indexes for the same loop use the skip-scan algorithm.
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SHA1: c52f7971e90cac1058d6b66c9e334cbc8607def3
User & Date: drh 2014-11-18 21:45:35
Context
2014-11-18
21:54
Adding the "noskipscan" token to an sqlite_stat1.stat field prevents an index for being used with the skip-scan algorithm. check-in: 4461bf04 user: drh tags: trunk
21:45
Allow an automatic index to be used if the only uses of declared indexes for the same loop use the skip-scan algorithm. check-in: c52f7971 user: drh tags: trunk
20:49
Merge in all the other ROLLBACK fixes from the branch-3.8.7 branch. I don't know why I was doing them one-by-one. check-in: 296b0c73 user: drh tags: trunk
2014-11-14
19:34
Consider using an automatic-index for a scan even if there exists a possible skip-scan that uses one or more "=" operators. Closed-Leaf check-in: 93642a65 user: dan tags: experimental-autoindex-fix
Changes
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Changes to src/where.c.

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    /* whereLoopAddBtree() always generates and inserts the automatic index
    ** case first.  Hence compatible candidate WhereLoops never have a larger
    ** rSetup. Call this SETUP-INVARIANT */
    assert( p->rSetup>=pTemplate->rSetup );

    /* Any loop using an appliation-defined index (or PRIMARY KEY or
    ** UNIQUE constraint) with one or more == constraints is better
    ** than an automatic index. */
    if( (p->wsFlags & WHERE_AUTO_INDEX)!=0

     && (pTemplate->wsFlags & WHERE_INDEXED)!=0
     && (pTemplate->wsFlags & WHERE_COLUMN_EQ)!=0
     && (p->prereq & pTemplate->prereq)==pTemplate->prereq
    ){
      break;
    }








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    /* whereLoopAddBtree() always generates and inserts the automatic index
    ** case first.  Hence compatible candidate WhereLoops never have a larger
    ** rSetup. Call this SETUP-INVARIANT */
    assert( p->rSetup>=pTemplate->rSetup );

    /* Any loop using an appliation-defined index (or PRIMARY KEY or
    ** UNIQUE constraint) with one or more == constraints is better
    ** than an automatic index. Unless it is a skip-scan. */
    if( (p->wsFlags & WHERE_AUTO_INDEX)!=0
     && (pTemplate->nSkip)==0
     && (pTemplate->wsFlags & WHERE_INDEXED)!=0
     && (pTemplate->wsFlags & WHERE_COLUMN_EQ)!=0
     && (p->prereq & pTemplate->prereq)==pTemplate->prereq
    ){
      break;
    }

Changes to test/autoindex3.test.

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# focus of this script is testing automatic index creation logic,
# and specifically that an automatic index will not be created that
# shadows a declared index.
#

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


# The t1b and t2d indexes are not very selective.  It used to be that
# the autoindex mechanism would create automatic indexes on t1(b) or
# t2(d), make assumptions that they were reasonably selective, and use
# them instead of t1b or t2d.  But that would be cheating, because the
# automatic index cannot be any more selective than the real index.
#
................................................................................
} {/AUTO/}
do_execsql_test autoindex3-130 {
  EXPLAIN QUERY PLAN SELECT * FROM t1, t2 WHERE d IS NULL AND x=y;
} {/AUTO/}
do_execsql_test autoindex3-140 {
  EXPLAIN QUERY PLAN SELECT * FROM t1, t2 WHERE d IN (5,b) AND x=y;
} {/AUTO/}



































finish_test







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# focus of this script is testing automatic index creation logic,
# and specifically that an automatic index will not be created that
# shadows a declared index.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
set testprefix autoindex3

# The t1b and t2d indexes are not very selective.  It used to be that
# the autoindex mechanism would create automatic indexes on t1(b) or
# t2(d), make assumptions that they were reasonably selective, and use
# them instead of t1b or t2d.  But that would be cheating, because the
# automatic index cannot be any more selective than the real index.
#
................................................................................
} {/AUTO/}
do_execsql_test autoindex3-130 {
  EXPLAIN QUERY PLAN SELECT * FROM t1, t2 WHERE d IS NULL AND x=y;
} {/AUTO/}
do_execsql_test autoindex3-140 {
  EXPLAIN QUERY PLAN SELECT * FROM t1, t2 WHERE d IN (5,b) AND x=y;
} {/AUTO/}

reset_db
do_execsql_test 210 {
  CREATE TABLE v(b, d, e);
  CREATE TABLE u(a, b, c);
  ANALYZE sqlite_master;
  INSERT INTO "sqlite_stat1" VALUES('u','uab','40000 400 1');
  INSERT INTO "sqlite_stat1" VALUES('v','vbde','40000 400 1 1');
  INSERT INTO "sqlite_stat1" VALUES('v','ve','40000 21');

  CREATE INDEX uab on u(a, b);
  CREATE INDEX ve on v(e);
  CREATE INDEX vbde on v(b,d,e);

  DROP TABLE IF EXISTS sqlite_stat4;
  ANALYZE sqlite_master;
}

# At one point, SQLite was using the inferior plan:
#
#   0|0|1|SEARCH TABLE v USING INDEX ve (e>?)
#   0|1|0|SEARCH TABLE u USING COVERING INDEX uab (ANY(a) AND b=?)
#
# on the basis that the real index "uab" must be better than the automatic
# index. This is not right - a skip-scan is not necessarily better than an
# automatic index scan.
#
do_eqp_test 220 {
  select count(*) from u, v where u.b = v.b and v.e > 34;
} {
  0 0 1 {SEARCH TABLE v USING INDEX ve (e>?)} 
  0 1 0 {SEARCH TABLE u USING AUTOMATIC COVERING INDEX (b=?)}
}


finish_test