doc/src/sgml/test-decoding.sgml

   1 <!-- doc/src/sgml/test-decoding.sgml -->
   2
   3 <sect1 id="test-decoding" xreflabel="test_decoding">
   4  <title>test_decoding &mdash; SQL-based test/example module for WAL logical decoding</title>
   5
   6  <indexterm zone="test-decoding">
   7   <primary>test_decoding</primary>
   8  </indexterm>
   9
  10  <para>
  11   <filename>test_decoding</filename> is an example of a logical decoding
  12   output plugin. It doesn't do anything especially useful, but can serve as
  13   a starting point for developing your own output plugin.
  14  </para>
  15
  16  <para>
  17   <filename>test_decoding</filename> receives WAL through the logical decoding
  18   mechanism and decodes it into text representations of the operations
  19   performed.
  20  </para>
  21
  22  <para>
  23   Typical output from this plugin, used over the SQL logical decoding
  24   interface, might be:
  25
  26 <programlisting>
  27 postgres=# SELECT * FROM pg_logical_slot_get_changes('test_slot', NULL, NULL, 'include-xids', '0');
  28    lsn     | xid |                       data
  29 -----------+-----+--------------------------------------------------
  30  0/16D30F8 | 691 | BEGIN
  31  0/16D32A0 | 691 | table public.data: INSERT: id[int4]:2 data[text]:'arg'
  32  0/16D32A0 | 691 | table public.data: INSERT: id[int4]:3 data[text]:'demo'
  33  0/16D32A0 | 691 | COMMIT
  34  0/16D32D8 | 692 | BEGIN
  35  0/16D3398 | 692 | table public.data: DELETE: id[int4]:2
  36  0/16D3398 | 692 | table public.data: DELETE: id[int4]:3
  37  0/16D3398 | 692 | COMMIT
  38 (8 rows)
  39 </programlisting>
  40  </para>
  41
  42 <para>
  43   We can also get the changes of the in-progress transaction, and the typical
  44   output might be:
  45
  46 <programlisting>
  47 postgres[33712]=#* SELECT * FROM pg_logical_slot_get_changes('test_slot', NULL, NULL, 'stream-changes', '1');
  48     lsn    | xid |                       data
  49 -----------+-----+--------------------------------------------------
  50  0/16B21F8 | 503 | opening a streamed block for transaction TXN 503
  51  0/16B21F8 | 503 | streaming change for TXN 503
  52  0/16B2300 | 503 | streaming change for TXN 503
  53  0/16B2408 | 503 | streaming change for TXN 503
  54  0/16BEBA0 | 503 | closing a streamed block for transaction TXN 503
  55  0/16B21F8 | 503 | opening a streamed block for transaction TXN 503
  56  0/16BECA8 | 503 | streaming change for TXN 503
  57  0/16BEDB0 | 503 | streaming change for TXN 503
  58  0/16BEEB8 | 503 | streaming change for TXN 503
  59  0/16BEBA0 | 503 | closing a streamed block for transaction TXN 503
  60 (10 rows)
  61 </programlisting>
  62  </para>
  63
  64 </sect1>