Skip empty transaction stream in test_decoding.

We were decoding empty transactions via streaming APIs added in commit
45fdc9738b even when the user used the option 'skip-empty-xacts'. The APIs
makes no effort to skip empty xacts under the assumption that we will
never try to stream such transactions. However, that is not true because
we can pick to stream a transaction that has change messages for
REORDER_BUFFER_CHANGE_INTERNAL_SNAPSHOT and we don't send such messages to
downstream rather they are just to update the internal state. So, we need
to skip such xacts when plugin uses the option 'skip-empty-xacts'.

Diagnosed-By: Amit Kapila
Author: Dilip Kumar
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/CAA4eK1+OqgFNZkf7=ETe_y5ntjgDk3T0wcdkd4Sot_u1hySGfw@mail.gmail.com

1 files changed, 37 insertions, 0 deletions

diff --git a/contrib/test_decoding/specs/concurrent_stream.spec b/contrib/test_decoding/specs/concurrent_stream.spec
new file mode 100644
index 00000000000..ad9fde9c284
--- /dev/null
+++ b/contrib/test_decoding/specs/concurrent_stream.spec
@@ -0,0 +1,37 @@
+# Test decoding of in-progress transaction containing dml and a concurrent
+# transaction with ddl operation. The transaction containing ddl operation
+# should not get streamed as it doesn't have any changes.
+
+setup
+{
+  SELECT 'init' FROM pg_create_logical_replication_slot('isolation_slot', 'test_decoding');
+
+  -- consume DDL
+  SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
+  CREATE OR REPLACE FUNCTION large_val() RETURNS TEXT LANGUAGE SQL AS 'select array_agg(md5(g::text))::text from generate_series(1, 80000) g';
+}
+
+teardown
+{
+    DROP TABLE IF EXISTS stream_test;
+    DROP TABLE IF EXISTS stream_test1;
+    SELECT 'stop' FROM pg_drop_replication_slot('isolation_slot');
+}
+
+session "s0"
+setup { SET synchronous_commit=on; }
+step "s0_begin" { BEGIN; }
+step "s0_ddl"   {CREATE TABLE stream_test1(data text);}
+
+# The transaction commit for s1_ddl will add the INTERNAL_SNAPSHOT change to
+# the currently running s0_ddl and we want to test that s0_ddl should not get
+# streamed when user asked to skip-empty-xacts.
+session "s1"
+setup { SET synchronous_commit=on; }
+step "s1_ddl"   { CREATE TABLE stream_test(data text); }
+step "s1_begin" { BEGIN; }
+step "s1_toast_insert" {INSERT INTO stream_test SELECT large_val();}
+step "s1_commit" { COMMIT; }
+step "s1_get_stream_changes" { SELECT data FROM pg_logical_slot_get_changes('isolation_slot', NULL,NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1');}
+
+permutation "s0_begin" "s0_ddl" "s1_ddl" "s1_begin" "s1_toast_insert" "s1_commit" "s1_get_stream_changes"