Re: [PATCHES] COPY with no WAL, in certain circumstances - Mailing list pgsql-hackers

Robert Treat <xzilla@users.sourceforge.net> writes:
> On Saturday 06 January 2007 16:36, Simon Riggs wrote:
> <snip>
>> BEGIN;
>> CREATE TABLE foo...
>> INSERT INTO foo    --uses WAL
>> COPY foo..    --no WAL
>> INSERT INTO foo    --uses WAL
>> COPY foo..    --no WAL
>> INSERT INTO foo    --uses WAL
>> COPY foo...    --no WAL
>> COMMIT;

> Is there some technical reason that the INSERT statements need to use WAL in
> these scenarios?

First, there's enough other overhead to an INSERT that you'd not save
much percentagewise.  Second, not using WAL doesn't come for free: the
cost is having to fsync the whole table afterwards.  So it really only
makes sense for commands that one can expect are writing pretty much
all of the table.  I could easily see it being a net loss for individual
INSERTs.

            regards, tom lane