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
simplyuses 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@belkam.com>
>> To: Simon Riggs <simon@2ndquadrant.com>
>> Cc: pgsql-general@postgresql.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?
>>
>>
>>