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From: Sergey Burladyan <eshkinkot@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Cc: Dmitriy Sarafannikov <dsarafannikov@yandex.ru>
Cc: Vladimir Borodin <root@simply.name>
Subject: Re: Broken hint bits (freeze)
Date: Tue, 20 Jun 2017 19:24:49 +0300
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Amit Kapila <amit.kapila16@gmail.com> writes:

> > I am not sure about rsync, in my production server I have for example
> > 111 GB in pg_xlog and if I run rsync for pg_xlog it must send ~ 40GB
> > of new WALs I think.
> >
>
> Isn't the difference between old and new is just the last WAL segment
> file?  What is the source of this difference?

Postgres generate WAL files forward, and at standby too :-(
For example:
=== master ===
$ psql -c 'select pg_current_xlog_insert_location()'
 pg_current_xlog_insert_location 
---------------------------------
 4ED09/34A74590
(1 row)

$ ls 9.2/main/pg_xlog/ | awk '/4ED0900000034/,/xxx/ { print }' | wc -l
2262
==============

=== standby ===
$ psql -c 'select pg_last_xlog_replay_location()'
 pg_last_xlog_replay_location 
------------------------------
 4ED0A/AECFD7B8
(1 row)

postgres@avi-sql29:~$ ls 9.2/main/pg_xlog/ | awk '/4ED0A000000AE/,/xxx/ { print }' | wc -l
2456
===============

See https://www.postgresql.org/docs/9.2/static/wal-configuration.html
> they are recycled (renamed to become the next segments in the numbered sequence)

-- 
Sergey Burladyan


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