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Re: Largeobject Access Controls (r2460)

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: "KaiGai Kohei" <kaigai(at)ak(dot)jp(dot)nec(dot)com>, "Greg Smith" <greg(at)2ndquadrant(dot)com>, "Robert Haas" <robertmhaas(at)gmail(dot)com>, "Takahiro Itagaki" <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, pgsql-hackers(at)postgresql(dot)org, "Jaime Casanova" <jcasanov(at)systemguards(dot)com(dot)ec>
Subject: Re: Largeobject Access Controls (r2460)
Date: 2010-01-22 20:55:24
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Lists: pgsql-hackers
"Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> writes:
> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> We've heard of people with many tens of thousands of
>> tables, and pg_dump speed didn't seem to be a huge bottleneck for
>> them (at least not in recent versions).  So I'm feeling we should
>> not dismiss the idea of one TOC entry per blob.
>> Thoughts?

> I suspect that 7 million BLOBs (and growing fast) would be a problem
> for this approach.  Of course, if we're atypical, we could stay with
> bytea if this changed.  Just a data point.

Do you have the opportunity to try an experiment on hardware similar to
what you're running that on?  Create a database with 7 million tables
and see what the dump/restore times are like, and whether
pg_dump/pg_restore appear to be CPU-bound or memory-limited when doing
it.  If they aren't, we could conclude that millions of TOC entries
isn't a problem.

A compromise we could consider is some sort of sub-TOC-entry scheme that
gets the per-BLOB entries out of the main speed bottlenecks, while still
letting us share most of the logic.  For instance, I suspect that the
first bottleneck in pg_dump would be the dependency sorting, but we
don't really need to sort all the blobs individually for that.

			regards, tom lane

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