<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>49.1. Logical Decoding Examples</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="logicaldecoding.html" title="Chapter 49. Logical Decoding" /><link rel="next" href="logicaldecoding-explanation.html" title="49.2. Logical Decoding Concepts" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">49.1. Logical Decoding Examples</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="logicaldecoding.html" title="Chapter 49. Logical Decoding">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="logicaldecoding.html" title="Chapter 49. Logical Decoding">Up</a></td><th width="60%" align="center">Chapter 49. Logical Decoding</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.12 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="logicaldecoding-explanation.html" title="49.2. Logical Decoding Concepts">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="LOGICALDECODING-EXAMPLE"><div class="titlepage"><div><div><h2 class="title" style="clear: both">49.1. Logical Decoding Examples</h2></div></div></div><p> The following example demonstrates controlling logical decoding using the SQL interface. </p><p> Before you can use logical decoding, you must set <a class="xref" href="runtime-config-wal.html#GUC-WAL-LEVEL">wal_level</a> to <code class="literal">logical</code> and <a class="xref" href="runtime-config-replication.html#GUC-MAX-REPLICATION-SLOTS">max_replication_slots</a> to at least 1. Then, you should connect to the target database (in the example below, <code class="literal">postgres</code>) as a superuser. </p><pre class="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'); slot_name | lsn -----------------+----------- regression_slot | 0/16B1970 (1 row) postgres=# SELECT slot_name, plugin, slot_type, database, active, restart_lsn, confirmed_flush_lsn FROM pg_replication_slots; slot_name | plugin | slot_type | database | active | restart_lsn | confirmed_flush_lsn -----------------+---------------+-----------+----------+--------+-------------+----------------- regression_slot | test_decoding | logical | postgres | f | 0/16A4408 | 0/16A4440 (1 row) postgres=# -- There are no changes to see yet postgres=# SELECT * FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL); lsn | xid | data -----+-----+------ (0 rows) postgres=# CREATE TABLE data(id serial primary key, data text); CREATE TABLE postgres=# -- DDL isn't replicated, so all you'll see is the transaction postgres=# SELECT * FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL); lsn | xid | data -----------+-------+-------------- 0/BA2DA58 | 10297 | BEGIN 10297 0/BA5A5A0 | 10297 | COMMIT 10297 (2 rows) postgres=# -- Once changes are read, they're consumed and not emitted postgres=# -- in a subsequent call: postgres=# SELECT * FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL); lsn | xid | data -----+-----+------ (0 rows) postgres=# BEGIN; postgres=# INSERT INTO data(data) VALUES('1'); postgres=# INSERT INTO data(data) VALUES('2'); postgres=# COMMIT; postgres=# SELECT * FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL); lsn | xid | data -----------+-------+--------------------------------------------------------- 0/BA5A688 | 10298 | BEGIN 10298 0/BA5A6F0 | 10298 | table public.data: INSERT: id[integer]:1 data[text]:'1' 0/BA5A7F8 | 10298 | table public.data: INSERT: id[integer]:2 data[text]:'2' 0/BA5A8A8 | 10298 | COMMIT 10298 (4 rows) postgres=# INSERT INTO data(data) VALUES('3'); postgres=# -- You can also peek ahead in the change stream without consuming changes postgres=# SELECT * FROM pg_logical_slot_peek_changes('regression_slot', NULL, NULL); lsn | xid | data -----------+-------+--------------------------------------------------------- 0/BA5A8E0 | 10299 | BEGIN 10299 0/BA5A8E0 | 10299 | table public.data: INSERT: id[integer]:3 data[text]:'3' 0/BA5A990 | 10299 | COMMIT 10299 (3 rows) postgres=# -- The next call to pg_logical_slot_peek_changes() returns the same changes again postgres=# SELECT * FROM pg_logical_slot_peek_changes('regression_slot', NULL, NULL); lsn | xid | data -----------+-------+--------------------------------------------------------- 0/BA5A8E0 | 10299 | BEGIN 10299 0/BA5A8E0 | 10299 | table public.data: INSERT: id[integer]:3 data[text]:'3' 0/BA5A990 | 10299 | COMMIT 10299 (3 rows) postgres=# -- options can be passed to output plugin, to influence the formatting postgres=# SELECT * FROM pg_logical_slot_peek_changes('regression_slot', NULL, NULL, 'include-timestamp', 'on'); lsn | xid | data -----------+-------+--------------------------------------------------------- 0/BA5A8E0 | 10299 | BEGIN 10299 0/BA5A8E0 | 10299 | table public.data: INSERT: id[integer]:3 data[text]:'3' 0/BA5A990 | 10299 | COMMIT 10299 (at 2017-05-10 12:07:21.272494-04) (3 rows) postgres=# -- Remember to destroy a slot you no longer need to stop it consuming postgres=# -- server resources: postgres=# SELECT pg_drop_replication_slot('regression_slot'); pg_drop_replication_slot ----------------------- (1 row) </pre><p> The following example shows how logical decoding is controlled over the streaming replication protocol, using the program <a class="xref" href="app-pgrecvlogical.html" title="pg_recvlogical"><span class="refentrytitle"><span class="application">pg_recvlogical</span></span></a> included in the PostgreSQL distribution. This requires that client authentication is set up to allow replication connections (see <a class="xref" href="warm-standby.html#STREAMING-REPLICATION-AUTHENTICATION" title="26.2.5.1. Authentication">Section 26.2.5.1</a>) and that <code class="varname">max_wal_senders</code> is set sufficiently high to allow an additional connection. </p><pre class="programlisting"> $ pg_recvlogical -d postgres --slot=test --create-slot $ pg_recvlogical -d postgres --slot=test --start -f - <span class="keycap"><strong>Control</strong></span>+<span class="keycap"><strong>Z</strong></span> $ psql -d postgres -c "INSERT INTO data(data) VALUES('4');" $ fg BEGIN 693 table public.data: INSERT: id[integer]:4 data[text]:'4' COMMIT 693 <span class="keycap"><strong>Control</strong></span>+<span class="keycap"><strong>C</strong></span> $ pg_recvlogical -d postgres --slot=test --drop-slot </pre></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="logicaldecoding.html" title="Chapter 49. 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