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Do not use index if no limit or limit + offset > expected tuples unless enable_seqscan = off

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This commit is contained in:
Andrew Kane
2024-01-20 17:16:42 -08:00
parent a1a38156d7
commit 8b06719ae9
4 changed files with 154 additions and 0 deletions
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14
src/hnsw.c
View File

@@ -94,6 +94,20 @@ hnswcostestimate(PlannerInfo *root, IndexPath *path, double loop_count,
return;
}
/*
* Do not use index if no limit or limit + offset > ef_search unless
* enable_seqscan = off
*/
if (root->limit_tuples < 0 || root->limit_tuples > hnsw_ef_search)
{
*indexStartupCost = 1.0e10 - 1;
*indexTotalCost = 1.0e10 - 1;
*indexSelectivity = 0;
*indexCorrelation = 0;
*indexPages = 0;
return;
}
MemSet(&costs, 0, sizeof(costs));
index = index_open(path->indexinfo->indexoid, NoLock);

14
src/ivfflat.c
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@@ -105,6 +105,20 @@ ivfflatcostestimate(PlannerInfo *root, IndexPath *path, double loop_count,
*/
costs.numIndexTuples = path->indexinfo->tuples * ratio;
/*
* Do not use index if no limit or limit + offset > expected tuples unless
* enable_seqscan = off
*/
if (root->limit_tuples < 0 || root->limit_tuples > costs.numIndexTuples)
{
*indexStartupCost = 1.0e10 - 1;
*indexTotalCost = 1.0e10 - 1;
*indexSelectivity = 0;
*indexCorrelation = 0;
*indexPages = 0;
return;
}
#if PG_VERSION_NUM >= 120000
genericcostestimate(root, path, loop_count, &costs);
#else

64
test/t/019_ivfflat_limit.pl Normal file
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@@ -0,0 +1,64 @@
use strict;
use warnings;
use PostgresNode;
use TestLib;
use Test::More;
# Initialize node
my $node = get_new_node('node');
$node->init;
$node->start;
# Create table and index
$node->safe_psql("postgres", "CREATE EXTENSION vector;");
$node->safe_psql("postgres", "CREATE TABLE tst (v vector(3));");
$node->safe_psql("postgres",
"INSERT INTO tst SELECT ARRAY[random(), random(), random()] FROM generate_series(1, 1000) i;"
);
$node->safe_psql("postgres", "CREATE INDEX ON tst USING ivfflat (v vector_l2_ops) WITH (lists = 10);");
# Test limit
my $explain = $node->safe_psql("postgres", qq(
EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 100;
));
like($explain, qr/Index Scan/);
# Test limit with probes
$explain = $node->safe_psql("postgres", qq(
SET ivfflat.probes = 2;
EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 200;
));
like($explain, qr/Index Scan/);
# Test limit + offset
$explain = $node->safe_psql("postgres", qq(
EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 90 OFFSET 10;
));
like($explain, qr/Index Scan/);
# Test limit > expected tuples
$explain = $node->safe_psql("postgres", qq(
EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 101;
));
like($explain, qr/Seq Scan/);
# Test limit > expected tuples with probes
$explain = $node->safe_psql("postgres", qq(
SET ivfflat.probes = 2;
EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 201;
));
like($explain, qr/Seq Scan/);
# Test limit + offset > expected tuples
$explain = $node->safe_psql("postgres", qq(
EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 91 OFFSET 10;
));
like($explain, qr/Seq Scan/);
# Test no limit
$explain = $node->safe_psql("postgres", qq(
EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]';
));
like($explain, qr/Seq Scan/);
done_testing();

62
test/t/020_hnsw_limit.pl Normal file
View File

@@ -0,0 +1,62 @@
use strict;
use warnings;
use PostgresNode;
use TestLib;
use Test::More;
# Initialize node
my $node = get_new_node('node');
$node->init;
$node->start;
# Create table and index
$node->safe_psql("postgres", "CREATE EXTENSION vector;");
$node->safe_psql("postgres", "CREATE TABLE tst (v vector(3));");
$node->safe_psql("postgres",
"INSERT INTO tst SELECT ARRAY[random(), random(), random()] FROM generate_series(1, 1000) i;"
);
$node->safe_psql("postgres", "CREATE INDEX ON tst USING hnsw (v vector_l2_ops);");
# Test limit
my $explain = $node->safe_psql("postgres", qq(
EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 40;
));
like($explain, qr/Index Scan/);
# Test limit with CTE
$explain = $node->safe_psql("postgres", qq(
EXPLAIN ANALYZE WITH cte AS (SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 40) SELECT * FROM cte;
));
like($explain, qr/Index Scan/);
# Test limit + offset
$explain = $node->safe_psql("postgres", qq(
EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 30 OFFSET 10;
));
like($explain, qr/Index Scan/);
# Test limit > ef_search
$explain = $node->safe_psql("postgres", qq(
EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 41;
));
like($explain, qr/Seq Scan/);
# Test limit > ef_search with CTE
$explain = $node->safe_psql("postgres", qq(
EXPLAIN ANALYZE WITH cte AS (SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 41) SELECT * FROM cte;
));
like($explain, qr/Seq Scan/);
# Test limit + offset > ef_search
$explain = $node->safe_psql("postgres", qq(
EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]' LIMIT 31 OFFSET 10;
));
like($explain, qr/Seq Scan/);
# Test no limit
$explain = $node->safe_psql("postgres", qq(
EXPLAIN ANALYZE SELECT * FROM tst ORDER BY v <-> '[1,2,3]';
));
like($explain, qr/Seq Scan/);
done_testing();