On Mar 17, 2010, at 9:41 AM, Craig James wrote: > On 3/17/10 2:52 AM, Greg Stark wrote: >> On Wed, Mar 17, 2010 at 7:32 AM, Pierre C<li...@peufeu.com> wrote: >>>> I was thinking in something like that, except that the factor I'd use >>>> would be something like 50% or 100% of current size, capped at (say) 1 GB. >> >> This turns out to be a bad idea. One of the first thing Oracle DBAs >> are told to do is change this default setting to allocate some >> reasonably large fixed size rather than scaling upwards. >> >> This might be mostly due to Oracle's extent-based space management but >> I'm not so sure. Recall that the filesystem is probably doing some >> rounding itself. If you allocate 120kB it's probably allocating 128kB >> itself anyways. Having two layers rounding up will result in odd >> behaviour. >> >> In any case I was planning on doing this a while back. Then I ran some >> experiments and couldn't actually demonstrate any problem. ext2 seems >> to do a perfectly reasonable job of avoiding this problem. All the >> files were mostly large contiguous blocks after running some tests -- >> IIRC running pgbench. > > This is one of the more-or-less solved problems in Unix/Linux. Ext* file > systems have a "reserve" usually of 10% of the disk space that nobody except > root can use. It's not for root, it's because with 10% of the disk free, you > can almost always do a decent job of allocating contiguous blocks and get > good performance. Unless Postgres has some weird problem that Linux has > never seen before (and that wouldn't be unprecedented...), there's probably > no need to fool with file-allocation strategies. > > Craig >
Its fairly easy to break. Just do a parallel import with say, 16 concurrent tables being written to at once. Result? Fragmented tables. > -- > Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-performance -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
