On 30.11.2010 18:22, Robert Haas wrote:
> On Tue, Nov 30, 2010 at 11:16 AM, Tom Lane<tgl@sss.pgh.pa.us> wrote:
>> How much is "quite a lot"? Do we have any real reason to think that
>> this solution is unacceptable performance-wise?
>
> Well, let's imagine a 1GB insert-only table. It has 128K pages. If
> you XLOG setting the bit on each page, you'll need to write 128K WAL
> records, each containing a 12-byte relfilenode and a 4-byte block
> offset, for a total of 16 bytes of WAL per page, thus 2MB of WAL.
Plus WAL headers, I think it's something like 32 or 40 bytes of WAL per
page.
> But you did just dirty a gigabyte of data.
Good point.
-- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com
