Avoid Assert failure when processing empty statement in aborted xact.

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
index 0d6a295674873c06d0c86bca02bcab45fac4d166..21387fba9f10ac3afa7f4099498b38a1b35dcbaa 100644 (file)
--- a/src/backend/utils/cache/plancache.c
+++ b/src/backend/utils/cache/plancache.c
@@ -78,9 +78,11 @@
 /*
  * 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
index 9855abf2db77e4c90e5677af36db115493413dcf..29c6b2dae3bb9e04528807a068756702063b673b 100644 (file)
--- a/src/test/regress/expected/psql.out
+++ b/src/test/regress/expected/psql.out
@@ -237,6 +237,17 @@ 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
index 0a4be827d881ab8e70a1740f074a23401a27d472..94a54d6fd8d101f07586c6e3417a71284a63375d 100644 (file)
--- a/src/test/regress/sql/psql.sql
+++ b/src/test/regress/sql/psql.sql
@@ -119,6 +119,14 @@ 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);