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How to get parallel restore in PG 8.4 to work?

From: henk de wit <henk53602(at)hotmail(dot)com>
To: <pgsql-performance(at)postgresql(dot)org>
Subject: How to get parallel restore in PG 8.4 to work?
Date: 2009-03-31 22:57:34
Message-ID: COL104-W6288B22DCD85FC12769A2F58A0@phx.gbl (view raw or flat)
Thread:
Lists: pgsql-performance
Hi,
For performance reasons (obviously ;)) I'm experimenting with parallel restore in PG 8.4. I grabbed the latest source snapshot (of today, March 30) and compiled this with zlib support. I dumped a DB from PG 8.3.5 (using maximum compression). I got this message however:
postgres(at)mymachine:/home/henk/postgresql-8.4/bin$ time
./pg_restore -p 5434 -h localhost -U henk -d db_test -j 8 -Fc
/home/henk/test-databases/dumps/db_test.custom
pg_restore: [archiver] WARNING: archive is compressed, but this
installation does not support compression -- no data will be available
pg_restore: [archiver] cannot restore from compressed archive (compression
not supported in this installation)

So initially it seemed its only possible to do a pg_restore using the uncompressed pg_dump custom format. So I tried the uncompressed dump, but this too failed. This last part was a little problematic anyway, since pg_dump absolutely wants to read its input from a file and does not accept any input from stdin. I assume reading from a file is necessary for the multiple parallel processes to each read their own part of the file, something which might be difficult to do when reading from stdin.
Apart from the fact that it simply doesn't work for me at the moment, I see a major problem with this approach though. Dumping in the custom format (option -Fc) is far slower than dumping in the plain format. Even if the parallel restore would speed up things, then the combined time of a dump and restore would still be negatively affected when compared to doing a plain dump and restore. I'm aware of the fact that I might be hitting some bugs, as a development snapshot is by definition of course not stable. Also, perhaps I'm missing something.
My question is thus; could someone advise me how to get parallel restore to work and how to speed up a dump in the custom file format?
Many thanks in advance


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Subject: Re: How to get parallel restore in PG 8.4 to work?
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