Stabilize the test added by commit 022564f60c.

The test was unstable in branches 14 and 15 as we were relying on the
number of changes in the table having a toast column to start streaming.
On branches >= 16, we have a GUC debug_logical_replication_streaming which
can stream each change, so the test was stable in those branches.

Change the test to use PREPARE TRANSACTION as that should make the result
consistent and test the code changed in 022564f60c.

Reported-by: Daniel Gustafsson as per buildfarm
Author: Hou Zhijie, Amit Kapila
Backpatch-through: 14
Discussion: https://postgr.es/m/8C2F86AA-981E-4803-B14D-E264C0255330@yesql.se

4 files changed, 45 insertions, 38 deletions

diff --git a/contrib/test_decoding/expected/stream.out b/contrib/test_decoding/expected/stream.out
index 2e319a89417..0f21dcb8e0e 100644
--- a/contrib/test_decoding/expected/stream.out
+++ b/contrib/test_decoding/expected/stream.out
@@ -106,26 +106,6 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL,NULL, 'incl
  committing streamed transaction
 (17 rows)
 
--- Test that accessing a TOAST table in streaming mode is allowed.
--- Create a table with a column that uses a TOASTed default value.
--- (temporarily hide query, to avoid the long CREATE TABLE stmt)
-\set ECHO none
-BEGIN;
-INSERT INTO test_tab SELECT repeat('a', 6000) || g.i FROM generate_series(1, 350) g(i);
--- Force WAL flush, so that the above changes will be streamed.
-SELECT 'force flush' FROM pg_switch_wal();
-  ?column?   
--------------
- force flush
-(1 row)
-
-SELECT count(*) FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1');
- count 
--------
-   315
-(1 row)
-
-COMMIT;
 DROP TABLE stream_test;
 SELECT pg_drop_replication_slot('regression_slot');
  pg_drop_replication_slot 
diff --git a/contrib/test_decoding/expected/twophase.out b/contrib/test_decoding/expected/twophase.out
index e89dc74a5e4..22d128d431f 100644
--- a/contrib/test_decoding/expected/twophase.out
+++ b/contrib/test_decoding/expected/twophase.out
@@ -205,10 +205,33 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
  COMMIT
 (3 rows)
 
+-- Test that accessing a TOAST table is permitted during the decoding of a
+-- prepared transaction.
+-- Create a table with a column that uses a TOASTed default value.
+-- (temporarily hide query, to avoid the long CREATE TABLE stmt)
+\set ECHO none
+BEGIN;
+INSERT INTO test_tab VALUES('test');
+PREPARE TRANSACTION 'test_toast_table_access';
+SELECT count(*) FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1');
+ count 
+-------
+     3
+(1 row)
+
+COMMIT PREPARED 'test_toast_table_access';
+-- consume commit prepared
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1');
+                   data                    
+-------------------------------------------
+ COMMIT PREPARED 'test_toast_table_access'
+(1 row)
+
 -- Test 8:
 -- cleanup and make sure results are also empty
 DROP TABLE test_prepared1;
 DROP TABLE test_prepared2;
+DROP TABLE test_tab;
 -- show results. There should be nothing to show
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
  data 
diff --git a/contrib/test_decoding/sql/stream.sql b/contrib/test_decoding/sql/stream.sql
index 9502a6d87cf..4feec62972a 100644
--- a/contrib/test_decoding/sql/stream.sql
+++ b/contrib/test_decoding/sql/stream.sql
@@ -44,23 +44,5 @@ toasted-123456789012345678901234567890123456789012345678901234567890123456789012
 
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL,NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1');
 
--- Test that accessing a TOAST table in streaming mode is allowed.
-
--- Create a table with a column that uses a TOASTed default value.
--- (temporarily hide query, to avoid the long CREATE TABLE stmt)
-\set ECHO none
-SELECT 'CREATE TABLE test_tab (a text DEFAULT ''' || string_agg('toast value', '') || ''');' FROM generate_series(1, 4000)
-\gexec
-\set ECHO all
-
-BEGIN;
-INSERT INTO test_tab SELECT repeat('a', 6000) || g.i FROM generate_series(1, 350) g(i);
-
--- Force WAL flush, so that the above changes will be streamed.
-SELECT 'force flush' FROM pg_switch_wal();
-
-SELECT count(*) FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1');
-COMMIT;
-
 DROP TABLE stream_test;
 SELECT pg_drop_replication_slot('regression_slot');
diff --git a/contrib/test_decoding/sql/twophase.sql b/contrib/test_decoding/sql/twophase.sql
index aff5114eb10..0ff6ede1f38 100644
--- a/contrib/test_decoding/sql/twophase.sql
+++ b/contrib/test_decoding/sql/twophase.sql
@@ -104,10 +104,32 @@ COMMIT PREPARED 'test_prepared_nodecode';
 -- should be decoded now
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
 
+-- Test that accessing a TOAST table is permitted during the decoding of a
+-- prepared transaction.
+
+-- Create a table with a column that uses a TOASTed default value.
+-- (temporarily hide query, to avoid the long CREATE TABLE stmt)
+\set ECHO none
+SELECT 'CREATE TABLE test_tab (a text DEFAULT ''' || string_agg('toast value', '') || ''');' FROM generate_series(1, 4000)
+\gexec
+\set ECHO all
+
+BEGIN;
+INSERT INTO test_tab VALUES('test');
+PREPARE TRANSACTION 'test_toast_table_access';
+
+SELECT count(*) FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1');
+
+COMMIT PREPARED 'test_toast_table_access';
+
+-- consume commit prepared
+SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1', 'stream-changes', '1');
+
 -- Test 8:
 -- cleanup and make sure results are also empty
 DROP TABLE test_prepared1;
 DROP TABLE test_prepared2;
+DROP TABLE test_tab;
 -- show results. There should be nothing to show
 SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');