Re: "full_page_writes" makes no difference?

On Wed, May 4, 2011 at 7:16 AM, Tian Luo <jackrobin(at)gmail(dot)com> wrote:

> Hi guys,
>
> No matter I turn on or turn off the "full_page_writes", I always
> observe 8192-byte writes of log data for simple write operations
> (write/update).
>
>
Not sure how you measured it, but ISTM that the correct GUC to play with is
"fsync". If thats turned off, the WAL buffers won't be fsynced to the disk
at every commit. But that would mean reduced reliability in case of database
crash.

> But according to the document, when this is off, it could speed up
> operations but may cause problems during recovery. So, I guess this is
> because it writes less when the option is turned off. However, this
> contradicts my observations ....
>
>
When full_page_writes is turned off, the full page won't be backed up in the
WAL record after the first modification after a checkpoint. So yes, it can
reduce the amount of WAL written to the disk.

Thanks,
Pavan

--
Pavan Deolasee
EnterpriseDB http://www.enterprisedb.com