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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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10
doc/src/sgml/catalogs.sgml
View File

@ -11529,6 +11529,16 @@ SELECT * FROM pg_locks pl LEFT JOIN pg_prepared_xacts ppx
is <literal>-1</literal>.
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>two_phase</structfield> <type>bool</type>
</para>
<para>
True if the slot is enabled for decoding prepared transactions. Always
false for physical slots.
</para></entry>
</row>
</tbody>
</tgroup>
</table>

10
doc/src/sgml/func.sgml
View File

@ -25559,7 +25559,7 @@ postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
<indexterm>
<primary>pg_create_logical_replication_slot</primary>
</indexterm>
<function>pg_create_logical_replication_slot</function> ( <parameter>slot_name</parameter> <type>name</type>, <parameter>plugin</parameter> <type>name</type> <optional>, <parameter>temporary</parameter> <type>boolean</type> </optional> )
<function>pg_create_logical_replication_slot</function> ( <parameter>slot_name</parameter> <type>name</type>, <parameter>plugin</parameter> <type>name</type> <optional>, <parameter>temporary</parameter> <type>boolean</type>, <parameter>two_phase</parameter> <type>boolean</type> </optional> )
<returnvalue>record</returnvalue>
( <parameter>slot_name</parameter> <type>name</type>,
<parameter>lsn</parameter> <type>pg_lsn</type> )
@ -25571,9 +25571,11 @@ postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
parameter, <parameter>temporary</parameter>, when set to true, specifies that
the slot should not be permanently stored to disk and is only meant
for use by the current session. Temporary slots are also
released upon any error. A call to this function has the same
effect as the replication protocol command
<literal>CREATE_REPLICATION_SLOT ... LOGICAL</literal>.
released upon any error. The optional fourth parameter,
<parameter>two_phase</parameter>, when set to true, specifies
that the decoding of prepared transactions is enabled for this
slot. A call to this function has the same effect as the replication
protocol command <literal>CREATE_REPLICATION_SLOT ... LOGICAL</literal>.
</para></entry>
</row>

19
doc/src/sgml/logicaldecoding.sgml
View File

@ -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