Fix parallel-safety check of expressions and predicate for index builds

As coded, the planner logic that calculates the number of parallel
workers to use for a parallel index build uses expressions and
predicates from the relcache, which are flattened for the planner by
eval_const_expressions().

As reported in the bug, an immutable parallel-unsafe function flattened
in the relcache would become a Const, which would be considered as
parallel-safe, even if the predicate or the expressions including the
function are not safe in parallel workers.  Depending on the expressions
or predicate used, this could cause the parallel build to fail.

Tests are included that check parallel index builds with parallel-unsafe
predicate and expressions.  Two routines are added to lsyscache.h to be
able to retrieve expressions and predicate of an index from its pg_index
data.

Reported-by: Alexander Lakhin
Author: Tender Wang
Reviewed-by: Jian He, Michael Paquier
Discussion: https://postgr.es/m/CAHewXN=UaAaNn9ruHDH3Os8kxLVmtWqbssnf=dZN_s9=evHUFA@mail.gmail.com
Backpatch-through: 12

diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 65a9b0d802ac3a5c8ee403e47668cd088b5afe67..db00a593a65ad63bdb21b59a375f04153305dfaf 100644 (file)
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -6306,10 +6306,18 @@ plan_create_index_workers(Oid tableOid, Oid indexOid)
         * Currently, parallel workers can't access the leader's temporary tables.
         * Furthermore, any index predicate or index expressions must be parallel
         * safe.
+        *
+        * Fetch the list of expressions and predicates directly from the
+        * catalogs.  Retrieving this information from the relcache would cause
+        * the expressions and predicates to be flattened, losing properties that
+        * can be important to check if parallel workers can be used.  For
+        * example, immutable parallel-unsafe functions, that cannot be used in
+        * parallel workers, would be changed to Const nodes, that are safe in
+        * parallel workers.
         */
        if (heap->rd_rel->relpersistence == RELPERSISTENCE_TEMP ||
-               !is_parallel_safe(root, (Node *) RelationGetIndexExpressions(index)) ||
-               !is_parallel_safe(root, (Node *) RelationGetIndexPredicate(index)))
+               !is_parallel_safe(root, (Node *) get_index_expressions(indexOid)) ||
+               !is_parallel_safe(root, (Node *) get_index_predicate(indexOid)))
        {
                parallel_workers = 0;
                goto done;

diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 13f8dafa3081bce635a6042e0544dbdbf6d59533..db6b8a36ec94964744e128286f4d7fa9e2038e32 100644 (file)
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -3255,6 +3255,74 @@ get_index_column_opclass(Oid index_oid, int attno)
        return opclass;
 }
 
+/*
+ * get_index_expressions
+ *
+ *             Given the index OID, its a List of its expressions or NIL if none.
+ */
+List *
+get_index_expressions(Oid index_oid)
+{
+       List       *result;
+       HeapTuple       tuple;
+       Datum           exprDatum;
+       bool            isnull;
+       char       *exprString;
+
+       tuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(index_oid));
+       if (!HeapTupleIsValid(tuple))
+               elog(ERROR, "cache lookup failed for index %u", index_oid);
+
+       exprDatum = SysCacheGetAttr(INDEXRELID, tuple,
+                                                               Anum_pg_index_indexprs, &isnull);
+       if (isnull)
+       {
+               ReleaseSysCache(tuple);
+               return NIL;
+       }
+
+       exprString = TextDatumGetCString(exprDatum);
+       result = (List *) stringToNode(exprString);
+       pfree(exprString);
+       ReleaseSysCache(tuple);
+
+       return result;
+}
+
+/*
+ * get_index_predicate
+ *
+ *             Given the index OID, return a List of its predicate or NIL if none.
+ */
+List *
+get_index_predicate(Oid index_oid)
+{
+       List       *result;
+       HeapTuple       tuple;
+       Datum           predDatum;
+       bool            isnull;
+       char       *predString;
+
+       tuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(index_oid));
+       if (!HeapTupleIsValid(tuple))
+               elog(ERROR, "cache lookup failed for index %u", index_oid);
+
+       predDatum = SysCacheGetAttr(INDEXRELID, tuple,
+                                                               Anum_pg_index_indpred, &isnull);
+       if (isnull)
+       {
+               ReleaseSysCache(tuple);
+               return NIL;
+       }
+
+       predString = TextDatumGetCString(predDatum);
+       result = (List *) stringToNode(predString);
+       pfree(predString);
+       ReleaseSysCache(tuple);
+
+       return result;
+}
+
 /*
  * get_index_isreplident
  *

diff --git a/src/include/utils/lsyscache.h b/src/include/utils/lsyscache.h
index 53d4a2d1093469e6cf97f9c576d3ba8a814b987e..32ca83736eb857558e1633ee513773fae8ed02d1 100644 (file)
--- a/src/include/utils/lsyscache.h
+++ b/src/include/utils/lsyscache.h
@@ -182,6 +182,8 @@ extern char *get_namespace_name_or_temp(Oid nspid);
 extern Oid     get_range_subtype(Oid rangeOid);
 extern Oid     get_range_collation(Oid rangeOid);
 extern Oid     get_index_column_opclass(Oid index_oid, int attno);
+extern List *get_index_expressions(Oid index_oid);
+extern List *get_index_predicate(Oid index_oid);
 extern bool    get_index_isreplident(Oid index_oid);
 extern bool get_index_isvalid(Oid index_oid);
 extern bool get_index_isclustered(Oid index_oid);

diff --git a/src/test/regress/expected/btree_index.out b/src/test/regress/expected/btree_index.out
index f567117a4662780d17449e8c69ea7ba999394e12..8d0240f79beae9180f98127a95a0ccfe216aa467 100644 (file)
--- a/src/test/regress/expected/btree_index.out
+++ b/src/test/regress/expected/btree_index.out
@@ -330,3 +330,22 @@ VACUUM delete_test_table;
 -- The vacuum above should've turned the leaf page into a fast root. We just
 -- need to insert some rows to cause the fast root page to split.
 INSERT INTO delete_test_table SELECT i, 1, 2, 3 FROM generate_series(1,1000) i;
+-- Test with index expression and predicate that include a parallel unsafe
+-- function.
+CREATE FUNCTION para_unsafe_f() RETURNS int IMMUTABLE PARALLEL UNSAFE
+AS $$
+BEGIN
+    RETURN 0;
+EXCEPTION WHEN OTHERS THEN
+    RETURN 1;
+END$$ LANGUAGE plpgsql;
+CREATE TABLE btree_para_bld(i int);
+ALTER TABLE btree_para_bld SET (parallel_workers = 4);
+SET max_parallel_maintenance_workers TO 4;
+-- With parallel-unsafe expression
+CREATE INDEX ON btree_para_bld((i + para_unsafe_f()));
+-- With parallel-unsafe predicate
+CREATE INDEX ON btree_para_bld(i) WHERE i > para_unsafe_f();
+RESET max_parallel_maintenance_workers;
+DROP TABLE btree_para_bld;
+DROP FUNCTION para_unsafe_f;

diff --git a/src/test/regress/sql/btree_index.sql b/src/test/regress/sql/btree_index.sql
index 558dcae0ec7c5f9c4632f3a6417e7058927db48e..c80165c6ee784749b487a4baa01a285a8597df2b 100644 (file)
--- a/src/test/regress/sql/btree_index.sql
+++ b/src/test/regress/sql/btree_index.sql
@@ -160,3 +160,25 @@ VACUUM delete_test_table;
 -- The vacuum above should've turned the leaf page into a fast root. We just
 -- need to insert some rows to cause the fast root page to split.
 INSERT INTO delete_test_table SELECT i, 1, 2, 3 FROM generate_series(1,1000) i;
+
+-- Test with index expression and predicate that include a parallel unsafe
+-- function.
+CREATE FUNCTION para_unsafe_f() RETURNS int IMMUTABLE PARALLEL UNSAFE
+AS $$
+BEGIN
+    RETURN 0;
+EXCEPTION WHEN OTHERS THEN
+    RETURN 1;
+END$$ LANGUAGE plpgsql;
+
+CREATE TABLE btree_para_bld(i int);
+ALTER TABLE btree_para_bld SET (parallel_workers = 4);
+SET max_parallel_maintenance_workers TO 4;
+-- With parallel-unsafe expression
+CREATE INDEX ON btree_para_bld((i + para_unsafe_f()));
+-- With parallel-unsafe predicate
+CREATE INDEX ON btree_para_bld(i) WHERE i > para_unsafe_f();
+
+RESET max_parallel_maintenance_workers;
+DROP TABLE btree_para_bld;
+DROP FUNCTION para_unsafe_f;