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 87210fcf627de183942e5720cfc4b58b345fe63d..3d3f7a9beaeba6908d6c4d74a1afddf246968cbe 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 8f93028363682a9226ad41cc934bdf40bdf93fe4..c062c3dc7b5b6503b0b8f9d95fbd6c22ea767767 100644 (file)
--- a/src/test/regress/expected/psql.out
+++ b/src/test/regress/expected/psql.out
@@ -268,6 +268,17 @@ 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 630f638f02550a8f59eeaf67d1d58e2a5e348bd0..965021fd84dc95fcfd7c07ea419a570b1fc7027d 100644 (file)
--- a/src/test/regress/sql/psql.sql
+++ b/src/test/regress/sql/psql.sql
@@ -133,6 +133,14 @@ 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);