Re: Compression and on-disk sorting - Mailing list pgsql-hackers

From Tom Lane
Subject Re: Compression and on-disk sorting
Date
Msg-id 20432.1147880285@sss.pgh.pa.us
Whole thread Raw
In response to Re: Compression and on-disk sorting  ("Jim C. Nasby" <jnasby@pervasive.com>)
Responses Re: Compression and on-disk sorting
List pgsql-hackers
"Jim C. Nasby" <jnasby@pervasive.com> writes:
> What *might* make sense would be to provide two locations for pgsql_tmp,
> because a lot of operations in there involve reading and writing at the
> same time:

> Read from heap while writing tapes to pgsql_tmp
> read from tapes while writing final version to pgsql_tmp

Note that a large part of the reason for the current logtape.c design
is to avoid requiring 2X or more disk space to sort X amount of data.
AFAICS, any design that does the above will put us right back in the 2X
regime.  That's a direct, measurable penalty; it'll take more than
handwaving arguments to convince me we should change it in pursuit of
unquantified speed benefits.
        regards, tom lane


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