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  1. <?xml version="1.0" encoding="UTF-8" standalone="no"?>

  2. <!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>48.1. 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 V1.79.1" /><link rel="prev" href="logicaldecoding.html" title="Chapter 48. Logical Decoding" /><link rel="next" href="logicaldecoding-explanation.html" title="48.2. 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">48.1. Logical Decoding Examples</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="logicaldecoding.html" title="Chapter 48. Logical Decoding">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="logicaldecoding.html" title="Chapter 48. Logical Decoding">Up</a></td><th width="60%" align="center">Chapter 48. Logical Decoding</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="logicaldecoding-explanation.html" title="48.2. 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">48.1. Logical Decoding Examples</h2></div></div></div><p>

  3.     The following example demonstrates controlling logical decoding using the

  4.     SQL interface.

  5.    </p><p>

  6.     Before you can use logical decoding, you must set

  7.     <a class="xref" href="runtime-config-wal.html#GUC-WAL-LEVEL">wal_level</a> to <code class="literal">logical</code> and

  8.     <a class="xref" href="runtime-config-replication.html#GUC-MAX-REPLICATION-SLOTS">max_replication_slots</a> to at least 1.  Then, you

  9.     should connect to the target database (in the example

  10.     below, <code class="literal">postgres</code>) as a superuser.

  11.    </p><pre class="programlisting">

  12. postgres=# -- Create a slot named 'regression_slot' using the output plugin 'test_decoding'

  13. postgres=# SELECT * FROM pg_create_logical_replication_slot('regression_slot', 'test_decoding');

  14.     slot_name    |    lsn

  15. -----------------+-----------

  16.  regression_slot | 0/16B1970

  17. (1 row)

  18. 

  19. postgres=# SELECT slot_name, plugin, slot_type, database, active, restart_lsn, confirmed_flush_lsn FROM pg_replication_slots;

  20.     slot_name    |    plugin     | slot_type | database | active | restart_lsn | confirmed_flush_lsn

  21. -----------------+---------------+-----------+----------+--------+-------------+-----------------

  22.  regression_slot | test_decoding | logical   | postgres | f      | 0/16A4408   | 0/16A4440

  23. (1 row)

  24. 

  25. postgres=# -- There are no changes to see yet

  26. postgres=# SELECT * FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL);

  27.  lsn | xid | data 

  28. -----+-----+------

  29. (0 rows)

  30. 

  31. postgres=# CREATE TABLE data(id serial primary key, data text);

  32. CREATE TABLE

  33. 

  34. postgres=# -- DDL isn't replicated, so all you'll see is the transaction

  35. postgres=# SELECT * FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL);

  36.     lsn    |  xid  |     data     

  37. -----------+-------+--------------

  38.  0/BA2DA58 | 10297 | BEGIN 10297

  39.  0/BA5A5A0 | 10297 | COMMIT 10297

  40. (2 rows)

  41. 

  42. postgres=# -- Once changes are read, they're consumed and not emitted

  43. postgres=# -- in a subsequent call:

  44. postgres=# SELECT * FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL);

  45.  lsn | xid | data 

  46. -----+-----+------

  47. (0 rows)

  48. 

  49. postgres=# BEGIN;

  50. postgres=# INSERT INTO data(data) VALUES('1');

  51. postgres=# INSERT INTO data(data) VALUES('2');

  52. postgres=# COMMIT;

  53. 

  54. postgres=# SELECT * FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL);

  55.     lsn    |  xid  |                          data                           

  56. -----------+-------+---------------------------------------------------------

  57.  0/BA5A688 | 10298 | BEGIN 10298

  58.  0/BA5A6F0 | 10298 | table public.data: INSERT: id[integer]:1 data[text]:'1'

  59.  0/BA5A7F8 | 10298 | table public.data: INSERT: id[integer]:2 data[text]:'2'

  60.  0/BA5A8A8 | 10298 | COMMIT 10298

  61. (4 rows)

  62. 

  63. postgres=# INSERT INTO data(data) VALUES('3');

  64. 

  65. postgres=# -- You can also peek ahead in the change stream without consuming changes

  66. postgres=# SELECT * FROM pg_logical_slot_peek_changes('regression_slot', NULL, NULL);

  67.     lsn    |  xid  |                          data                           

  68. -----------+-------+---------------------------------------------------------

  69.  0/BA5A8E0 | 10299 | BEGIN 10299

  70.  0/BA5A8E0 | 10299 | table public.data: INSERT: id[integer]:3 data[text]:'3'

  71.  0/BA5A990 | 10299 | COMMIT 10299

  72. (3 rows)

  73. 

  74. postgres=# -- The next call to pg_logical_slot_peek_changes() returns the same changes again

  75. postgres=# SELECT * FROM pg_logical_slot_peek_changes('regression_slot', NULL, NULL);

  76.     lsn    |  xid  |                          data                           

  77. -----------+-------+---------------------------------------------------------

  78.  0/BA5A8E0 | 10299 | BEGIN 10299

  79.  0/BA5A8E0 | 10299 | table public.data: INSERT: id[integer]:3 data[text]:'3'

  80.  0/BA5A990 | 10299 | COMMIT 10299

  81. (3 rows)

  82. 

  83. postgres=# -- options can be passed to output plugin, to influence the formatting

  84. postgres=# SELECT * FROM pg_logical_slot_peek_changes('regression_slot', NULL, NULL, 'include-timestamp', 'on');

  85.     lsn    |  xid  |                          data                           

  86. -----------+-------+---------------------------------------------------------

  87.  0/BA5A8E0 | 10299 | BEGIN 10299

  88.  0/BA5A8E0 | 10299 | table public.data: INSERT: id[integer]:3 data[text]:'3'

  89.  0/BA5A990 | 10299 | COMMIT 10299 (at 2017-05-10 12:07:21.272494-04)

  90. (3 rows)

  91. 

  92. postgres=# -- Remember to destroy a slot you no longer need to stop it consuming

  93. postgres=# -- server resources:

  94. postgres=# SELECT pg_drop_replication_slot('regression_slot');

  95.  pg_drop_replication_slot

  96. -----------------------

  97. 

  98. (1 row)

  99. </pre><p>

  100.     The following example shows how logical decoding is controlled over the

  101.     streaming replication protocol, using the

  102.     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

  103.     distribution.  This requires that client authentication is set up to allow

  104.     replication connections

  105.     (see <a class="xref" href="warm-standby.html#STREAMING-REPLICATION-AUTHENTICATION" title="26.2.5.1. Authentication">Section 26.2.5.1</a>) and

  106.     that <code class="varname">max_wal_senders</code> is set sufficiently high to allow

  107.     an additional connection.

  108.    </p><pre class="programlisting">

  109. $ pg_recvlogical -d postgres --slot=test --create-slot

  110. $ pg_recvlogical -d postgres --slot=test --start -f -

  111. <span class="keycap"><strong>Control</strong></span>+<span class="keycap"><strong>Z</strong></span>

  112. $ psql -d postgres -c "INSERT INTO data(data) VALUES('4');"

  113. $ fg

  114. BEGIN 693

  115. table public.data: INSERT: id[integer]:4 data[text]:'4'

  116. COMMIT 693

  117. <span class="keycap"><strong>Control</strong></span>+<span class="keycap"><strong>C</strong></span>

  118. $ pg_recvlogical -d postgres --slot=test --drop-slot

  119. </pre></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="logicaldecoding.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="logicaldecoding.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="logicaldecoding-explanation.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 48. Logical Decoding </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 48.2. Logical Decoding Concepts</td></tr></table></div></body></html>
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