On Mon, Aug 20, 2012 at 6:44 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> On Mon, Aug 20, 2012 at 4:27 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> Surely we could just prevent creation of the FSM until the table has
>>> reached at least, say, 10 blocks.
>>>
>>> Any threshold beyond one block would mean potential space wastage,
>>> but it's hard to get excited about that until you're into the dozens
>>> of pages.
>
>> I dunno, I think one-row tables are pretty common.
>
> Sure, and for that you don't need an FSM, because any row allocation
> attempt will default to trying the last existing block before it extends
> (see RelationGetBufferForTuple). It's only once you've got more than
> one block in the table that it becomes interesting.
>
> If we had a convention that FSM is only created for rels of more than
> N blocks, perhaps it'd be worthwhile to teach RelationGetBufferForTuple
> to try all existing blocks when relation size <= N. Or equivalently,
> hack the FSM code to return all N pages when it has no info.
Now that's an idea I could get behind. I'd pick a smaller value of N
than what you suggested (10), perhaps 5. But I like it otherwise.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company