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Add option to enable two_phase commits via pg_create_logical_replication_slot.

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Commit 0aa8a01d04 extends the output plugin API to allow decoding of
prepared xacts and allowed the user to enable/disable the two-phase option
via pg_logical_slot_get_changes(). This can lead to a problem such that
the first time when it gets changes via pg_logical_slot_get_changes()
without two_phase option enabled it will not get the prepared even though
prepare is after consistent snapshot. Now next time during getting changes,
if the two_phase option is enabled it can skip prepare because by that
time start decoding point has been moved. So the user will only get commit
prepared.

Allow to enable/disable this option at the create slot time and default
will be false. It will break the existing slots which is fine in a major
release.

Author: Ajin Cherian
Reviewed-by: Amit Kapila and Vignesh C
Discussion: https://postgr.es/m/d0f60d60-133d-bf8d-bd70-47784d8fabf3@enterprisedb.com
This commit is contained in:
Amit Kapila
2021-03-03 07:28:43 +05:30
parent ee28cacf61
commit 19890a064e
20 changed files with 131 additions and 93 deletions
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19
doc/src/sgml/logicaldecoding.sgml
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@@ -55,7 +55,7 @@
<programlisting>
postgres=# -- Create a slot named 'regression_slot' using the output plugin 'test_decoding'
postgres=# SELECT * FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');
postgres=# SELECT * FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding', false, true);
slot_name | lsn
-----------------+-----------
regression_slot | 0/16B1970
@@ -169,17 +169,18 @@ $ pg_recvlogical -d postgres --slot=test --drop-slot
<para>
The following example shows SQL interface that can be used to decode prepared
transactions. Before you use two-phase commit commands, you must set
<varname>max_prepared_transactions</varname> to at least 1. You must also set
the option 'two-phase-commit' to 1 while calling
<function>pg_logical_slot_get_changes</function>. Note that we will stream
the entire transaction after the commit if it is not already decoded.
<varname>max_prepared_transactions</varname> to at least 1. You must also have
set the two-phase parameter as 'true' while creating the slot using
<function>pg_create_logical_replication_slot</function>
Note that we will stream the entire transaction after the commit if it
is not already decoded.
</para>
<programlisting>
postgres=# BEGIN;
postgres=*# INSERT INTO data(data) VALUES('5');
postgres=*# PREPARE TRANSACTION 'test_prepared1';
postgres=# SELECT * FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'two-phase-commit', '1');
postgres=# SELECT * FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL);
lsn | xid | data
-----------+-----+---------------------------------------------------------
0/1689DC0 | 529 | BEGIN 529
@@ -188,7 +189,7 @@ postgres=# SELECT * FROM pg_logical_slot_get_changes('regression_slot', NULL, NU
(3 rows)
postgres=# COMMIT PREPARED 'test_prepared1';
postgres=# select * from pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'two-phase-commit', '1');
postgres=# select * from pg_logical_slot_get_changes('regression_slot', NULL, NULL);
lsn | xid | data
-----------+-----+--------------------------------------------
0/168A060 | 529 | COMMIT PREPARED 'test_prepared1', txid 529
@@ -198,7 +199,7 @@ postgres=#-- you can also rollback a prepared transaction
postgres=# BEGIN;
postgres=*# INSERT INTO data(data) VALUES('6');
postgres=*# PREPARE TRANSACTION 'test_prepared2';
postgres=# select * from pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'two-phase-commit', '1');
postgres=# select * from pg_logical_slot_get_changes('regression_slot', NULL, NULL);
lsn | xid | data
-----------+-----+---------------------------------------------------------
0/168A180 | 530 | BEGIN 530
@@ -207,7 +208,7 @@ postgres=# select * from pg_logical_slot_get_changes('regression_slot', NULL, NU
(3 rows)
postgres=# ROLLBACK PREPARED 'test_prepared2';
postgres=# select * from pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'two-phase-commit', '1');
postgres=# select * from pg_logical_slot_get_changes('regression_slot', NULL, NULL);
lsn | xid | data
-----------+-----+----------------------------------------------
0/168A4B8 | 530 | ROLLBACK PREPARED 'test_prepared2', txid 530