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xlog location arithmetic

From: Euler Taveira de Oliveira <euler(at)timbira(dot)com>
To: Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: xlog location arithmetic
Date: 2011-12-06 04:19:49
Message-ID: 4EDD97E5.8080201@timbira.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Hi,

A while ago when blogging about WAL [1], I noticed a function to deal with
xlog location arithmetic is wanted. I remembered Depez [2] mentioning it and
after some questions during trainings and conferences I decided to translate
my shell script function in C.

The attached patch implements the function pg_xlog_location_diff (bikeshed
colors are welcome). It calculates the difference between two given
transaction log locations. Now that we have pg_stat_replication view, it will
be easy to get the lag just passing columns as parameters. Also, the
monitoring tools could take advantage of it instead of relying on a fragile
routine to get the lag.

I noticed that pg_xlogfile_name* functions does not sanity check the xrecoff
boundaries but that is material for another patch.


[1] http://eulerto.blogspot.com/2011/11/understanding-wal-nomenclature.html
[2]
http://www.depesz.com/index.php/2011/01/24/waiting-for-9-1-pg_stat_replication/


-- 
   Euler Taveira de Oliveira - Timbira       http://www.timbira.com.br/
   PostgreSQL: Consultoria, Desenvolvimento, Suporte 24x7 e Treinamento

Attachment: xlogdiff.patch
Description: text/x-patch (5.1 KB)

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