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
<alvherre@commandprompt.com> wrote:
Tom Lane escribió:
> Alvaro Herrera <
alvherre@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.
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.
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