Fix fetching default toast value during decoding of in-progress transactions.

During logical decoding of in-progress transactions, we perform the toast
table scan while fetching the default toast value for an attribute. We
forgot to initialize the flag during this scan to indicate that the system
table scan is in progress. We need this flag to ensure that during logical
decoding we never directly access the tableam or heap APIs because we check
for concurrent aborts only in systable_* APIs.

Reported-by: Alexander Lakhin
Author: Takeshi Ideriha, Hou Zhijie
Reviewed-by: Amit Kapila, Hou Zhijie
Backpatch-through: 14
Discussion: https://postgr.es/m/18641-6687273b7f15269d@postgresql.org

diff --git a/contrib/test_decoding/expected/stream.out b/contrib/test_decoding/expected/stream.out
index 0f21dcb8e0e442c14079ea99426b0d3a27f952b5..d4bfbf975db5ff05ba0a0add16647fa48183e786 100644 (file)
--- a/contrib/test_decoding/expected/stream.out
+++ b/contrib/test_decoding/expected/stream.out
@@ -106,6 +106,28 @@ 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
+SET debug_logical_replication_streaming = immediate;
+BEGIN;
+INSERT INTO test_tab VALUES(1);
+-- 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 
+-------
+     3
+(1 row)
+
+COMMIT;
+RESET debug_logical_replication_streaming;
 DROP TABLE stream_test;
 SELECT pg_drop_replication_slot('regression_slot');
  pg_drop_replication_slot 

diff --git a/contrib/test_decoding/sql/stream.sql b/contrib/test_decoding/sql/stream.sql
index 4feec62972a5e4b6ac40fddbaed3fc8836d645a7..0549d3204a2c981acc88c1ec25d19b7fadd284f4 100644 (file)
--- a/contrib/test_decoding/sql/stream.sql
+++ b/contrib/test_decoding/sql/stream.sql
@@ -44,5 +44,27 @@ 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
+
+SET debug_logical_replication_streaming = immediate;
+
+BEGIN;
+INSERT INTO test_tab VALUES(1);
+
+-- 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;
+
+RESET debug_logical_replication_streaming;
+
 DROP TABLE stream_test;
 SELECT pg_drop_replication_slot('regression_slot');

diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
index 16c7aa9fbf5bbebab7bcc7a386d5be7284c6d7c2..e3b626b30303ace239737f2570dac55b3a3a5929 100644 (file)
--- a/src/backend/access/index/genam.c
+++ b/src/backend/access/index/genam.c
@@ -703,6 +703,14 @@ systable_beginscan_ordered(Relation heapRelation,
    index_rescan(sysscan->iscan, key, nkeys, NULL, 0);
    sysscan->scan = NULL;
 
+   /*
+    * If CheckXidAlive is set then set a flag to indicate that system table
+    * scan is in-progress.  See detailed comments in xact.c where these
+    * variables are declared.
+    */
+   if (TransactionIdIsValid(CheckXidAlive))
+       bsysscan = true;
+
    return sysscan;
 }
 
@@ -747,6 +755,14 @@ systable_endscan_ordered(SysScanDesc sysscan)
    index_endscan(sysscan->iscan);
    if (sysscan->snapshot)
        UnregisterSnapshot(sysscan->snapshot);
+
+   /*
+    * Reset the bsysscan flag at the end of the systable scan.  See detailed
+    * comments in xact.c where these variables are declared.
+    */
+   if (TransactionIdIsValid(CheckXidAlive))
+       bsysscan = false;
+
    pfree(sysscan);
 }