Re: unlogged tables

On Sun, Nov 21, 2010 at 11:07 PM, Andy Colson <andy(at)squeakycode(dot)net> wrote:
> After all this... there are too many numbers for me.  I have no idea what
> this means.

I think what it means that is that, for you, unlogged tables were
almost as fast as shutting off all of synchronous_commit,
full_page_writes, and fsync, and further setting
bgwriter_lru_maxpages=0. Now, that seems a little strange, because
you'd think if anything it would be faster. I'm not sure what
accounts for the difference, although I wonder if checkpoints are part
of it. With the current code, which doesn't exclude unlogged table
pages from checkpoints, a checkpoint will still be faster with
fsync=off than with unlogged tables. It seems like we're agreed that
this is a problem to be fixed in phase two, though, either by fsyncing
every unlogged table we can find at shutdown time, or else by
providing two durability options, one that works as the current code
does (but survives clean shutdowns) and another that excludes dirty
pages from checkpoints (and does not survive clean shutdowns).

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company