Message-ID: <467B3459.9030808@oss.ntt.co.jp>
Date: Fri, 22 Jun 2007 11:30:49 +0900
From: Toru SHIMOGAKI <shimogaki.toru@oss.ntt.co.jp>
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To: Tom Lane <tgl@sss.pgh.pa.us>, Dan Gorman <dgorman@hi5.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: PITR Backups
References: <7E0807EE-B970-4869-A248-B838E42AD9EE@hi5.com>
	<9761.1182472005@sss.pgh.pa.us>
In-Reply-To: <9761.1182472005@sss.pgh.pa.us>
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Tom Lane wrote:
> Dan Gorman <dgorman@hi5.com> writes:
>>    All of our databases are on NetApp storage and I have been looking  
>> at SnapMirror (PITR RO copy ) and FlexClone (near instant RW volume  
>> replica) for backing up our databases. The problem is because there  
>> is no write-suspend or even a 'hot backup mode' for postgres it's  
>> very plausible that the database has data in RAM that hasn't been  
>> written and will corrupt the data.

> Alternatively, you can use a PITR base backup as suggested here:
> http://www.postgresql.org/docs/8.2/static/continuous-archiving.html

I think Dan's problem is important if we use PostgreSQL to a large size database:

- When we take a PITR base backup with hardware level snapshot operation
  (not filesystem level) which a lot of storage vender provide, the backup data
  can be corrupted as Dan said. During recovery we can't even read it,
  especially if meta-data was corrupted.

- If we don't use hardware level snapshot operation, it takes long time to take
  a large backup data, and a lot of full-page-written WAL files are made.

So, I think users need a new feature not to write out heap pages during taking a
backup.

Any comments?

Best regards,

-- 
Toru SHIMOGAKI<shimogaki.toru@oss.ntt.co.jp>
NTT Open Source Software Center