Re: effects of posix_fadvise on WAL logs

On Tue, 26 May 2009, Mark Wong wrote:

> Maybe there isn't enough activity to the WAL relative to the rest of the 
> database to show anything interesting?

Maybe you could reduce checkpoint_segments and focus on UPDATEs?  That's 
how I've been able to generate the most WAL activity relative to database 
writes in the past, because of the full_page_writes behavior.  Quoth the 
docs:  "To ensure data page consistency, the first modification of a data 
page after each checkpoint results in logging the entire page content. In 
that case, a smaller checkpoint interval increases the volume of output to 
the WAL log, partially negating the goal of using a smaller interval, and 
in any case causing more disk I/O."

You've got checkpoint_segments set to 3000 in your tests and 
checkpoint_time to 1 hour, which means the tests you ran are really 
generating minimal WAL volume.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD