From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Zoltan Boszormenyi <zb(at)cybertec(dot)at> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: What's the difference between SET STORAGE MAIN and EXTENDED? |
Date: | 2007-09-07 15:45:50 |
Message-ID: | 22599.1189179950@sss.pgh.pa.us |
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Lists: | pgsql-general |
Zoltan Boszormenyi <zb(at)cybertec(dot)at> writes:
> Tom Lane =EDrta:
>> Zoltan Boszormenyi <zb(at)cybertec(dot)at> writes:
>>> At the end of the day, the behaviour is the same, isn't it?
>>
>> No, there's a difference in terms of the priority for pushing this
>> column out to toast storage, versus pushing other columns of the row
>> out to toast.
> Thanks very much for clarifying.
> I was thinking of a binary data that wouldn't fit
> into the maximum inline tuple size. In this case
> both MAIN and EXTENDED end up compressed
> and out-of-line. I didn't consider having multiple
> bytea or text columns filled with small amount of data.
It'd be pretty unwise to mark a column MAIN if it's likely to contain
wide values ("wide" meaning more than 1K or so). As you say, it'll
still get toasted --- but not until after everything else in the row has
been toasted, even quite narrow values that happen to be of toastable
types.
regards, tom lane
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