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 80ad6bf1741c0f07965d99b478a5371893299ec6..a06e5edf6dbbc3c8d1505f67cbbc6f1ea149ba6c 100644 (file)
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -6695,10 +6695,18 @@ 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 60978f9415b33d1dd125ee76336ca57c619a09e2..b6e9a35d9c59f512eb7f217d4492e59da52fd0e8 100644 (file)
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -3504,6 +3504,74 @@ 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 4f5418b9728fdbb852ed0bc1690b9a80c20a20eb..7ca3bb3b1222251be9d77c286c196e7d9d1934b6 100644 (file)
--- a/src/include/utils/lsyscache.h
+++ b/src/include/utils/lsyscache.h
@@ -195,6 +195,8 @@ extern Oid  get_range_collation(Oid rangeOid);
 extern Oid get_range_multirange(Oid rangeOid);
 extern Oid get_multirange_range(Oid multirangeOid);
 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 93ed5e8cc00ea08463cb46840c7628c37ce27e82..cd94a636f7da6d2985b7bd77e40cd3c03213a0c2 100644 (file)
--- a/src/test/regress/expected/btree_index.out
+++ b/src/test/regress/expected/btree_index.out
@@ -387,3 +387,22 @@ ALTER INDEX btree_part_idx ALTER COLUMN id SET (n_distinct=100);
 ERROR:  ALTER action ALTER COLUMN ... SET cannot be performed on relation "btree_part_idx"
 DETAIL:  This operation is not supported for partitioned indexes.
 DROP TABLE btree_part;
+-- 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 239f4a4755f042832a55e44a030f893e29a10245..91934be48a1d9758ead0d72aa2e3faba7c1b0b70 100644 (file)
--- a/src/test/regress/sql/btree_index.sql
+++ b/src/test/regress/sql/btree_index.sql
@@ -242,3 +242,25 @@ CREATE TABLE btree_part (id int4) PARTITION BY RANGE (id);
 CREATE INDEX btree_part_idx ON btree_part(id);
 ALTER INDEX btree_part_idx ALTER COLUMN id SET (n_distinct=100);
 DROP TABLE btree_part;
+
+-- 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;