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<!-- doc/src/sgml/test-decoding.sgml -->
<sect1 id="test-decoding" xreflabel="test_decoding">
<title>test_decoding</title>
<indexterm zone="test-decoding">
<primary>test_decoding</primary>
</indexterm>
<para>
<filename>test_decoding</filename> is an example of a logical decoding
output plugin. It doesn't do anything especially useful, but can serve as
a starting point for developing your own output plugin.
</para>
<para>
<filename>test_decoding</filename> receives WAL through the logical decoding
mechanism and decodes it into text representations of the operations
performed.
</para>
<para>
Typical output from this plugin, used over the SQL logical decoding
interface, might be:
<programlisting>
postgres=# SELECT * FROM pg_logical_slot_get_changes('test_slot', NULL, NULL, 'include-xids', '0');
lsn | xid | data
-----------+-----+--------------------------------------------------
0/16D30F8 | 691 | BEGIN
0/16D32A0 | 691 | table public.data: INSERT: id[int4]:2 data[text]:'arg'
0/16D32A0 | 691 | table public.data: INSERT: id[int4]:3 data[text]:'demo'
0/16D32A0 | 691 | COMMIT
0/16D32D8 | 692 | BEGIN
0/16D3398 | 692 | table public.data: DELETE: id[int4]:2
0/16D3398 | 692 | table public.data: DELETE: id[int4]:3
0/16D3398 | 692 | COMMIT
(8 rows)
</programlisting>
</para>
<para>
We can also get the changes of the in-progress transaction, and the typical
output might be:
<programlisting>
postgres[33712]=#* SELECT * FROM pg_logical_slot_get_changes('test_slot', NULL, NULL, 'stream-changes', '1');
lsn | xid | data
-----------+-----+--------------------------------------------------
0/16B21F8 | 503 | opening a streamed block for transaction TXN 503
0/16B21F8 | 503 | streaming change for TXN 503
0/16B2300 | 503 | streaming change for TXN 503
0/16B2408 | 503 | streaming change for TXN 503
0/16BEBA0 | 503 | closing a streamed block for transaction TXN 503
0/16B21F8 | 503 | opening a streamed block for transaction TXN 503
0/16BECA8 | 503 | streaming change for TXN 503
0/16BEDB0 | 503 | streaming change for TXN 503
0/16BEEB8 | 503 | streaming change for TXN 503
0/16BEBA0 | 503 | closing a streamed block for transaction TXN 503
(10 rows)
</programlisting>
</para>
</sect1>
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