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Add function pg_xlog_location_diff to help comparisons

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Comparing two xlog locations are useful for example when calculating
replication lag.

Euler Taveira de Oliveira, reviewed by Fujii Masao, and some cleanups
from me
This commit is contained in:
Magnus Hagander
2012-03-04 12:15:24 +01:00
parent 0e5e167aae
commit bc5ac36865
5 changed files with 114 additions and 2 deletions
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20
doc/src/sgml/func.sgml
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@ -14475,11 +14475,15 @@ SELECT set_config('log_statement_stats', 'off', false);
<indexterm>
<primary>pg_xlogfile_name_offset</primary>
</indexterm>
<indexterm>
<primary>pg_xlog_location_diff</primary>
</indexterm>
<para>
The functions shown in <xref
linkend="functions-admin-backup-table"> assist in making on-line backups.
These functions cannot be executed during recovery.
These functions cannot be executed during recovery (except
<function>pg_xlog_location_diff</function>).
</para>
<table id="functions-admin-backup-table">
@ -14547,6 +14551,13 @@ SELECT set_config('log_statement_stats', 'off', false);
<entry><type>text</>, <type>integer</></entry>
<entry>Convert transaction log location string to file name and decimal byte offset within file</entry>
</row>
<row>
<entry>
<literal><function>pg_xlog_location_diff(<parameter>location</> <type>text</>, <parameter>location</> <type>text</>)</function></literal>
</entry>
<entry><type>numeric</></entry>
<entry>Calculate the difference between two transaction log locations</entry>
</row>
</tbody>
</tgroup>
</table>
@ -14639,6 +14650,13 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
needs to be archived.
</para>
<para>
<function>pg_xlog_location_diff</> calculates the difference in bytes
between two transaction log locations. It can be used with
<structname>pg_stat_replication</structname> or some functions shown in
<xref linkend="functions-admin-backup-table"> to get the replication lag.
</para>
<para>
For details about proper usage of these functions, see
<xref linkend="continuous-archiving">.