Re: please explain vacuum with WAL

From: Dmitry Melekhov <dm(at)belkam(dot)com>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: please explain vacuum with WAL
Date: 2008-07-08 08:54:57
Message-ID: 48732B61.4010708@belkam.com
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Simon Riggs пишет:
> On Tue, 2008-07-08 at 13:09 +0500, Dmitry Melekhov wrote:
>
>> Hello!
>>
>> I tried to ask this question in novice list.
>> Just because there are no replies I try here.
>> This is really novice question- I'm oracle dba :-)
>>
>>
>>> I just installed 8.3 with WAL enabled.
>>> But I can't understand why postgres generated many archive logs during
>>> vacuum, if WAL is enabled.
>>> Could you explain?
>>>
>
> What do you mean "WAL is enabled"? That's not a term I recognize since
> WAL is always enabled.
>
>
AFAIK, it can be disabled. May be I'm wrong...
> Best read this
> http://developer.postgresql.org/pgdocs/postgres/routine-vacuuming.html
>
> VACUUM needs to perform writes to clear up, which generates WAL.
>
>
This is what I don't understand.
I think WAL can be used for point-in-time recovery.
So, if I have database backup and WAL generated after this backup, I can
do recovery, this mean WAL already contains all changes to database,
without vacuum. Could you tell me what is wrong in my sentence?

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