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Re: Large number of open(2) calls with bulk INSERT into empty table

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Bruce Momjian <bruce(at)momjian(dot)us>, Florian Weimer <fweimer(at)bfk(dot)de>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Large number of open(2) calls with bulk INSERT into empty table
Date: 2012-08-21 13:52:02
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Lists: pgsql-hackers
On Mon, Aug 20, 2012 at 6:44 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Mon, Aug 20, 2012 at 4:27 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)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
The Enterprise PostgreSQL Company

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