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 5da863d85de74406d80edba03e190521a749a7db..88cb97f445f688182ee46d4ca8eeb5c1c9ca9955 100644 (file)
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -5911,10 +5911,18 @@ 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 5564b53f25727c28831386b9b4c19965d07cc5bc..3c232aa960faa450a2f5ef44774e83ae6cdd7f37 100644 (file)
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -3510,6 +3510,74 @@ 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 77871aaefc330c3c3f554af8bb7571fcd9178181..704543fa07c7e9feb7de0bd85a95dbe591ce2b8c 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 c7328b1dc4f9974a90facae470663f0bb25c4066..0463d72faa7ccd61a278a033f7a21ae2ea03c9e0 100644 (file)
--- a/src/test/regress/expected/btree_index.out
+++ b/src/test/regress/expected/btree_index.out
@@ -341,3 +341,22 @@ CREATE INDEX btree_part_idx ON btree_part(id);
 ALTER INDEX btree_part_idx ALTER COLUMN id SET (n_distinct=100);
 ERROR:  "btree_part_idx" is not a table, materialized view, or foreign table
 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 c34502249f3ed043b2621736310e7be2fa56681c..71d816223da8e1dc1594ce8f8ebf83ad4428b484 100644 (file)
--- a/src/test/regress/sql/btree_index.sql
+++ b/src/test/regress/sql/btree_index.sql
@@ -183,3 +183,25 @@ 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;