I agree with Tom, any reordering attempt is at best second guessing the filesystem and underlying storage.
However, having the ability to control the extent size would be a worthwhile improvement for systems that walk and chew gum (write to lots of tables) concurrently. I'm thinking of Oracle's AUTOEXTEND settings for tablespace datafiles .... I think the ideal way to do it for PG would be to make the equivalent configurable in postgresql.conf system wide, and allow specific per-table settings in the SQL metadata, similar to auto-vacuum. An awesomely simple alternative is to just specify the extension as e.g. 5% of the existing table size .... it starts by adding one block at a time for tiny tables, and once your table is over 20GB, it ends up adding a whole 1GB file and pre-allocating it. Very little wasteage. Cheers Dave On Tue, Mar 16, 2010 at 4:49 PM, Alvaro Herrera <alvhe...@commandprompt.com>wrote: > Tom Lane escribió: > > Alvaro Herrera <alvhe...@commandprompt.com> writes: > > > Maybe it would make more sense to try to reorder the fsync calls > > > instead. > > > > Reorder to what, though? You still have the problem that we don't know > > much about the physical layout on-disk. > > Well, to block numbers as a first step. > > However, this reminds me that sometimes we take the block-at-a-time > extension policy too seriously. We had a customer that had a > performance problem because they were inserting lots of data to TOAST > tables, causing very frequent extensions. I kept wondering whether an > allocation policy that allocated several new blocks at a time could be > useful (but I didn't try it). This would also alleviate fragmentation, > thus helping the physical layout be more similar to logical block > numbers. > > -- > Alvaro Herrera > http://www.CommandPrompt.com/ > PostgreSQL Replication, Consulting, Custom Development, 24x7 support >
