Ability to advance replication slots

Ability to advance both physical and logical replication slots using a
new user function pg_replication_slot_advance().

For logical advance that means records are consumed as fast as possible
and changes are not given to output plugin for sending. Makes 2nd phase
(after we reached SNAPBUILD_FULL_SNAPSHOT) of replication slot creation
faster, especially when there are big transactions as the reorder buffer
does not have to deal with data changes and does not have to spill to
disk.

Author: Petr Jelinek
Reviewed-by: Simon Riggs

2 files changed, 45 insertions, 0 deletions

diff --git a/contrib/test_decoding/expected/slot.out b/contrib/test_decoding/expected/slot.out
index 9f5f8a9b766..21e9d56f73b 100644
--- a/contrib/test_decoding/expected/slot.out
+++ b/contrib/test_decoding/expected/slot.out
@@ -92,6 +92,36 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot2', NULL, NULL, 'in
  COMMIT
 (3 rows)
 
+INSERT INTO replication_example(somedata, text) VALUES (1, 4);
+INSERT INTO replication_example(somedata, text) VALUES (1, 5);
+SELECT pg_current_wal_lsn() AS wal_lsn \gset
+INSERT INTO replication_example(somedata, text) VALUES (1, 6);
+SELECT end_lsn FROM pg_replication_slot_advance('regression_slot1', :'wal_lsn') \gset
+SELECT slot_name FROM pg_replication_slot_advance('regression_slot2', pg_current_wal_lsn());
+    slot_name     
+------------------
+ regression_slot2
+(1 row)
+
+SELECT :'wal_lsn' = :'end_lsn';
+ ?column? 
+----------
+ t
+(1 row)
+
+SELECT data FROM pg_logical_slot_get_changes('regression_slot1', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
+                                                  data                                                   
+---------------------------------------------------------------------------------------------------------
+ BEGIN
+ table public.replication_example: INSERT: id[integer]:6 somedata[integer]:1 text[character varying]:'6'
+ COMMIT
+(3 rows)
+
+SELECT data FROM pg_logical_slot_get_changes('regression_slot2', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
+ data 
+------
+(0 rows)
+
 DROP TABLE replication_example;
 -- error
 SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot1', 'test_decoding', true);
diff --git a/contrib/test_decoding/sql/slot.sql b/contrib/test_decoding/sql/slot.sql
index fa9561f54ea..706340c1d8d 100644
--- a/contrib/test_decoding/sql/slot.sql
+++ b/contrib/test_decoding/sql/slot.sql
@@ -45,6 +45,21 @@ INSERT INTO replication_example(somedata, text) VALUES (1, 3);
 SELECT data FROM pg_logical_slot_get_changes('regression_slot1', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
 SELECT data FROM pg_logical_slot_get_changes('regression_slot2', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
 
+INSERT INTO replication_example(somedata, text) VALUES (1, 4);
+INSERT INTO replication_example(somedata, text) VALUES (1, 5);
+
+SELECT pg_current_wal_lsn() AS wal_lsn \gset
+
+INSERT INTO replication_example(somedata, text) VALUES (1, 6);
+
+SELECT end_lsn FROM pg_replication_slot_advance('regression_slot1', :'wal_lsn') \gset
+SELECT slot_name FROM pg_replication_slot_advance('regression_slot2', pg_current_wal_lsn());
+
+SELECT :'wal_lsn' = :'end_lsn';
+
+SELECT data FROM pg_logical_slot_get_changes('regression_slot1', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
+SELECT data FROM pg_logical_slot_get_changes('regression_slot2', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');
+
 DROP TABLE replication_example;
 
 -- error