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Introduce logical decoding.

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This feature, building on previous commits, allows the write-ahead log
stream to be decoded into a series of logical changes; that is,
inserts, updates, and deletes and the transactions which contain them.
It is capable of handling decoding even across changes to the schema
of the effected tables.  The output format is controlled by a
so-called "output plugin"; an example is included.  To make use of
this in a real replication system, the output plugin will need to be
modified to produce output in the format appropriate to that system,
and to perform filtering.

Currently, information can be extracted from the logical decoding
system only via SQL; future commits will add the ability to stream
changes via walsender.

Andres Freund, with review and other contributions from many other
people, including Álvaro Herrera, Abhijit Menon-Sen, Peter Gheogegan,
Kevin Grittner, Robert Haas, Heikki Linnakangas, Fujii Masao, Abhijit
Menon-Sen, Michael Paquier, Simon Riggs, Craig Ringer, and Steve
Singer.
This commit is contained in:
Robert Haas
2014-03-03 16:32:18 -05:00
parent de94b47c0a
commit b89e151054
89 changed files with 12998 additions and 194 deletions
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1
doc/src/sgml/contrib.sgml
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@ -140,6 +140,7 @@ CREATE EXTENSION <replaceable>module_name</> FROM unpackaged;
&sslinfo;
&tablefunc;
&tcn;
&test-decoding;
&test-parser;
&test-shm-mq;
&tsearch2;

1
doc/src/sgml/filelist.sgml
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@ -143,6 +143,7 @@
<!ENTITY sslinfo SYSTEM "sslinfo.sgml">
<!ENTITY tablefunc SYSTEM "tablefunc.sgml">
<!ENTITY tcn SYSTEM "tcn.sgml">
<!ENTITY test-decoding SYSTEM "test-decoding.sgml">
<!ENTITY test-parser SYSTEM "test-parser.sgml">
<!ENTITY test-shm-mq SYSTEM "test-shm-mq.sgml">
<!ENTITY tsearch2 SYSTEM "tsearch2.sgml">

42
doc/src/sgml/test-decoding.sgml Normal file
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@ -0,0 +1,42 @@
<!-- 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</> 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 decoder.
</para>
<para>
<filename>test_decoding</> 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', 'now', 'include-xids', '0');
location | 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>
</sect1>