Re: Wal -long transaction

From: Greg Stark <gsstark(at)mit(dot)edu>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Martijn van Oosterhout <kleptog(at)svana(dot)org>, Agnes Bocchino <agnes(dot)bocchino(at)bull(dot)net>, pgsql-general(at)postgresql(dot)org
Subject: Re: Wal -long transaction
Date: 2006-03-13 18:35:44
Message-ID: 873bhmkxa7.fsf@stark.xeocode.com
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Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> Of course, there's no free lunch --- the price we pay for escaping
> rollback-segment-overflow is table bloat if you don't vacuum often
> enough.

Well it's worse than that. If you have long-running transactions that would
cause rollback-segment-overflow in Oracle then the equivalent price in
Postgres would be table bloat *regardless* of how frequently you vacuum.

I suppose you can argue it's not "bloat" as long as you reach a steady state.
But the extra space in the tables is a performance cost on every sequential
scan and on every cache miss it causes whatever you call it.

I'm not saying I like rollback segments better, just yes, TANSTAAFL.

--
greg

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