Re: please explain vacuum with WAL

Glyn Astill пишет:
> WAL is the journal for postgres, so every event that happens goes into the WAL. Using it for backup or replication simply uses it to replay all events on the backup / replicated database.
>
>
>
>

As I thought, thank you.
But why vacuum generates WAL ? As I understand all database changes are
already logged....

> ----- Original Message ----
>
>> From: Dmitry Melekhov <dm(at)belkam(dot)com>
>> To: Simon Riggs <simon(at)2ndquadrant(dot)com>
>> Cc: pgsql-general(at)postgresql(dot)org
>> Sent: Tuesday, 8 July, 2008 9:54:57 AM
>> Subject: Re: [GENERAL] please explain vacuum with WAL
>>
>> 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?
>>
>>
>>