On Thursday 16 December 2010 23:34:02 Heikki Linnakangas wrote: > On 17.12.2010 00:29, Andres Freund wrote: > > On Thursday 16 December 2010 19:33:10 Joachim Wieland wrote: > >> On Thu, Dec 16, 2010 at 12:48 PM, Heikki Linnakangas > >> > >> <heikki.linnakan...@enterprisedb.com> wrote: > >>> As soon as we have parallel pg_dump, the next big thing is going to be > >>> parallel dump of the same table using multiple processes. Perhaps we > >>> should prepare for that in the directory archive format, by allowing > >>> the data of a single table to be split into multiple files. That way > >>> parallel pg_dump is simple, you just split the table in chunks of > >>> roughly the same size, say 10GB each, and launch a process for each > >>> chunk, writing to a separate file. > >> > >> How exactly would you "just split the table in chunks of roughly the > >> same size" ? Which queries should pg_dump send to the backend? If it > >> just sends a bunch of WHERE queries, the server would still scan the > >> same data several times since each pg_dump client would result in a > >> seqscan over the full table. > > > > I would suggest implementing< > support for tidscans and doing it in > > segment size... > > I don't think there's any particular gain from matching the server's > data file segment size, although 1GB does sound like a good chunk size > for this too. Its noticeable more efficient reading from different files in different processes in comparison to all hammering the same file.
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