Don't enter parallel mode when holding interrupts.

Doing so caused the leader to hang in wait_event=ParallelFinish, which
required an immediate shutdown to resolve.  Back-patch to v12 (all
supported versions).

Francesco Degrassi

Discussion: https://postgr.es/m/CAC-SaSzHUKT=vZJ8MPxYdC_URPfax+yoA1hKTcF4ROz_Q6z0_Q@mail.gmail.com

diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 821693c60ee27f3c1300d91ae3bbdcbaf0ebbe56..f533d2c7dc95b112261d1dc8174c76d74a29bda8 100644 (file)
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -332,6 +332,11 @@ standard_planner(Query *parse, const char *query_string, int cursorOptions,
     * if we want to allow parallel inserts in general; updates and deletes
     * have additional problems especially around combo CIDs.)
     *
+    * We don't try to use parallel mode unless interruptible.  The leader
+    * expects ProcessInterrupts() calls to reach HandleParallelMessages().
+    * Even if we called HandleParallelMessages() another way, starting a
+    * parallel worker is too delay-prone to be prudent when uncancellable.
+    *
     * For now, we don't try to use parallel mode if we're running inside a
     * parallel worker.  We might eventually be able to relax this
     * restriction, but for now it seems best not to have parallel workers
@@ -342,6 +347,7 @@ standard_planner(Query *parse, const char *query_string, int cursorOptions,
        parse->commandType == CMD_SELECT &&
        !parse->hasModifyingCTE &&
        max_parallel_workers_per_gather > 0 &&
+       INTERRUPTS_CAN_BE_PROCESSED() &&
        !IsParallelWorker())
    {
        /* all the cheap tests pass, so scan the query tree */

diff --git a/src/test/regress/expected/select_parallel.out b/src/test/regress/expected/select_parallel.out
index 7906a3a5c0c99fc6f99754f236b979c5e1af8c7c..ac32a1bc9be0903df67db8234a40b8bb81a847ea 100644 (file)
--- a/src/test/regress/expected/select_parallel.out
+++ b/src/test/regress/expected/select_parallel.out
@@ -1254,3 +1254,27 @@ reset force_parallel_mode;
 drop function set_and_report_role();
 drop function set_role_and_error(int);
 drop role regress_parallel_worker;
+-- don't freeze in ParallelFinish while holding an LWLock
+BEGIN;
+CREATE FUNCTION my_cmp (int4, int4)
+RETURNS int LANGUAGE sql AS
+$$
+   SELECT
+       CASE WHEN $1 < $2 THEN -1
+               WHEN $1 > $2 THEN  1
+               ELSE 0
+       END;
+$$;
+CREATE TABLE parallel_hang (i int4);
+INSERT INTO parallel_hang
+   (SELECT * FROM generate_series(1, 400) gs);
+CREATE OPERATOR CLASS int4_custom_ops FOR TYPE int4 USING btree AS
+   OPERATOR 1 < (int4, int4), OPERATOR 2 <= (int4, int4),
+   OPERATOR 3 = (int4, int4), OPERATOR 4 >= (int4, int4),
+   OPERATOR 5 > (int4, int4), FUNCTION 1 my_cmp(int4, int4);
+CREATE UNIQUE INDEX parallel_hang_idx
+                   ON parallel_hang
+                   USING btree (i int4_custom_ops);
+SET force_parallel_mode = on;
+DELETE FROM parallel_hang WHERE 380 <= i AND i <= 420;
+ROLLBACK;

diff --git a/src/test/regress/sql/select_parallel.sql b/src/test/regress/sql/select_parallel.sql
index 39870f0141d258ac364de55789a4387f0273575d..f4e8c8a1aa38bb2c24ec34931d7abe5e81fedfbc 100644 (file)
--- a/src/test/regress/sql/select_parallel.sql
+++ b/src/test/regress/sql/select_parallel.sql
@@ -487,3 +487,34 @@ reset force_parallel_mode;
 drop function set_and_report_role();
 drop function set_role_and_error(int);
 drop role regress_parallel_worker;
+
+-- don't freeze in ParallelFinish while holding an LWLock
+BEGIN;
+
+CREATE FUNCTION my_cmp (int4, int4)
+RETURNS int LANGUAGE sql AS
+$$
+   SELECT
+       CASE WHEN $1 < $2 THEN -1
+               WHEN $1 > $2 THEN  1
+               ELSE 0
+       END;
+$$;
+
+CREATE TABLE parallel_hang (i int4);
+INSERT INTO parallel_hang
+   (SELECT * FROM generate_series(1, 400) gs);
+
+CREATE OPERATOR CLASS int4_custom_ops FOR TYPE int4 USING btree AS
+   OPERATOR 1 < (int4, int4), OPERATOR 2 <= (int4, int4),
+   OPERATOR 3 = (int4, int4), OPERATOR 4 >= (int4, int4),
+   OPERATOR 5 > (int4, int4), FUNCTION 1 my_cmp(int4, int4);
+
+CREATE UNIQUE INDEX parallel_hang_idx
+                   ON parallel_hang
+                   USING btree (i int4_custom_ops);
+
+SET force_parallel_mode = on;
+DELETE FROM parallel_hang WHERE 380 <= i AND i <= 420;
+
+ROLLBACK;