Avoid Assert failure when processing empty statement in aborted xact.

tglsfdc · tglsfdc · commit a8be2356c556 · 2023-06-21T11:07:11.000-04:00
exec_parse_message() wants to create a cached plan in all cases, including for empty input. The empty-input path does not have a test for being in an aborted transaction, making it possible that plancache.c will fail due to trying to do database lookups even though there's no real work to do. One solution would be to throw an aborted-transaction error in this path too, but it's not entirely clear whether the lack of such an error was intentional or whether some clients might be relying on non-error behavior. Instead, let's hack plancache.c so that it treats empty statements with the same logic it already had for transaction control commands, ensuring that it can soldier through even in an already-aborted transaction. Per bug #17983 from Alexander Lakhin. Back-patch to all supported branches. Discussion: https://postgr.es/m/17983-da4569fcb878672e@postgresql.org
diff --git a/src/backend/utils/cache/plancache.c b/src/backend/utils/cache/plancache.c
@@ -74,9 +74,11 @@
 /*
  * We must skip "overhead" operations that involve database access when the
  * cached plan's subject statement is a transaction control command.
+ * For the convenience of postgres.c, treat empty statements as control
+ * commands too.
  */
 #define IsTransactionStmtPlan(plansource)  \
-	((plansource)->raw_parse_tree && \
+	((plansource)->raw_parse_tree == NULL || \
 	 IsA((plansource)->raw_parse_tree->stmt, TransactionStmt))
 
 /*
diff --git a/src/test/regress/expected/psql.out b/src/test/regress/expected/psql.out
@@ -215,6 +215,17 @@ SELECT 3 AS x, 'Hello', 4 AS y, true AS "dirty\name" \gdesc \g
  3 | Hello    | 4 | t
 (1 row)
 
+-- test for server bug #17983 with empty statement in aborted transaction
+set search_path = default;
+begin;
+bogus;
+ERROR:  syntax error at or near "bogus"
+LINE 1: bogus;
+        ^
+;
+\gdesc
+The command has no result, or the result has no columns.
+rollback;
 -- \gexec
 create temporary table gexec_test(a int, b text, c date, d float);
 select format('create index on gexec_test(%I)', attname)
diff --git a/src/test/regress/sql/psql.sql b/src/test/regress/sql/psql.sql
@@ -112,6 +112,14 @@ SELECT 1 AS x, 'Hello', 2 AS y, true AS "dirty\name"
 -- all on one line
 SELECT 3 AS x, 'Hello', 4 AS y, true AS "dirty\name" \gdesc \g
 
+-- test for server bug #17983 with empty statement in aborted transaction
+set search_path = default;
+begin;
+bogus;
+;
+\gdesc
+rollback;
+
 -- \gexec
 
 create temporary table gexec_test(a int, b text, c date, d float);
