Merge #139265

139265: opt: remove incorrect query plans for trigram similarity filters r=normanchenn a=normanchenn

Previously, the optimizer would produce incorrect query plans for queries with trigram similarity filters when `pg_trgm.similarity_threshold == 0`, producing incorrect results.

To address this, this patch adds a check to return early if `pg_trgm.similarity_threshold == 0` in trigram similarity queries on inverted indices.

Fixes: #122443

Release note (bug fix): The optimizer could produce incorrect query plans for queries using trigram similarity filters (e.g. `col % 'val'`) when `pg_trgm.similarity_threshold` was set to 0. This bug was introduced in v22.2.0 and is now fixed. Note that this issue does not affect v24.2.0+ releases when the `optimizer_use_trigram_similarity_optimization` session variable (introduced in v24.2.0) is set to its default value `true`, as it would skip this behaviour.

Co-authored-by: Norman Chen <[email protected]>

pkg/sql/logictest/testdata/logic_test/trigram_indexes

@@ -358,3 +358,29 @@ FROM
             AS tab (col1_1, col1_2) ON
             (tab2.col1) = (tab.col1_1)
             AND (tab2.col2) = (tab.col1_2);
+
+subtest trigram_similarity_zero_threshold_inverted_index
+
+statement ok
+SET pg_trgm.similarity_threshold =  0;
+
+statement ok
+CREATE TABLE trigram_similarity_zero_threshold_inverted_index_a (
+  a INT PRIMARY KEY,
+  b STRING,
+  INVERTED INDEX c (b gin_trgm_ops)
+);
+
+statement ok
+SET optimizer_use_trigram_similarity_optimization = false;
+
+statement error pq: index "c" is inverted and cannot be used for this query
+SELECT * FROM trigram_similarity_zero_threshold_inverted_index_a@c WHERE b % 'foo';
+
+statement ok
+SET optimizer_use_trigram_similarity_optimization = true;
+
+statement error pq: index "c" is inverted and cannot be used for this query
+SELECT * FROM trigram_similarity_zero_threshold_inverted_index_a@c WHERE b % 'foo';
+
+subtest end

pkg/sql/opt/invertedidx/trigram.go

@@ -72,6 +72,12 @@ func (t *trigramFilterPlanner) extractInvertedFilterConditionFromLeaf(
 		if evalCtx.SessionData().OptimizerUseTrigramSimilarityOptimization {
 			return inverted.NonInvertedColExpression{}, expr, nil
 		}
+
+		// Do not plan inverted index scans when the trigram similarity threshold is 0
+		// because all strings will be matched.
+		if evalCtx.SessionData().TrigramSimilarityThreshold == 0 {
+			return inverted.NonInvertedColExpression{}, expr, nil
+		}
 		// If we're doing a % expression (similarity threshold), we need to
 		// construct an OR out of the spans: we need to find results that match any
 		// of the trigrams in the constant datum, and we'll filter the results

pkg/sql/opt/invertedidx/trigram_test.go

@@ -23,6 +23,7 @@ func TestTryFilterTrigram(t *testing.T) {
 	semaCtx := tree.MakeSemaContext(nil /* resolver */)
 	st := cluster.MakeTestingClusterSettings()
 	evalCtx := eval.NewTestingEvalContext(st)
+	evalCtx.SessionData().TrigramSimilarityThreshold = 0.3
 
 	tc := testcat.New()
 	if _, err := tc.ExecuteDDL(