From: Sergey Burladyan <eshkinkot@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Bruce Momjian <bruce@momjian.us>,
  PostgreSQL-development <pgsql-hackers@postgresql.org>,
  Dmitriy Sarafannikov <dsarafannikov@yandex.ru>,
  Vladimir Borodin <root@simply.name>
Subject: Re: Broken hint bits (freeze)
References: <C4ADB713-CF88-4A75-A3C3-10E4E0A750DB@simply.name>
	<20170613193124.GQ13873@momjian.us> <87mv98af8j.fsf@seb.koffice.internal>
	<CAA4eK1JB=5gHNhRWgtVcqCQbUzGwR2LM9msYBQVULDfA+1ugUA@mail.gmail.com>
	<20170616164641.GP11450@momjian.us> <87fuezalc3.fsf@seb.koffice.internal>
	<CAA4eK1KMxzg_q2-0rMRh22EMWGutQ0QbCtMqc_5GeuNVyJ8kmA@mail.gmail.com>
	<20170619222113.GF3180@momjian.us>
	<CAJ2ymdg=0knii-bavVLpKEGc9DanaZC+UXjnipx_n-gFvOkdcg@mail.gmail.com>
	<20170620025919.GA28277@momjian.us> <20170620033726.GB28277@momjian.us>
	<87h8zb6kbx.fsf@seb.koffice.internal>
	<CAA4eK1JmEAj9qUMbS-=u7b4Boqsr3mAoadevT9LDWm4JgxamBg@mail.gmail.com>
	<8760fq7pfe.fsf@seb.koffice.internal>
	<CAA4eK1JxV1+UTyU3T2WM6rhiDEZy6zk3cx+Y3TaXCXAwQxcU1Q@mail.gmail.com>
Date: Tue, 20 Jun 2017 19:24:49 +0300
In-Reply-To: 
 <CAA4eK1JxV1+UTyU3T2WM6rhiDEZy6zk3cx+Y3TaXCXAwQxcU1Q@mail.gmail.com> (Amit
	Kapila's message of "Tue, 20 Jun 2017 19:24:41 +0530")
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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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