Re: How to move a database from HP server to Linux Server that had already one database.

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От Kevin Grittner
Тема Re: How to move a database from HP server to Linux Server that had already one database.
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Msg-id 4C61116402000025000343F3@gw.wicourts.gov
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Ответ на Re: How to move a database from HP server to Linux Server that had already one database.  (Bruce Momjian <bruce@momjian.us>)
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Bruce Momjian <bruce@momjian.us> wrote:
> ENGEMANN, DAYSE wrote:

>>  pg_dump -h sourcemachine -U sourceuser source_dbname \
>>   | psql target_dbname
>
> Has anyone done any measurement of whether it is faster to do the
> dump on the local machine with psql remote or from a remote
> machine (where psql would be local)?

I haven't, because I want to dump with the pg_dump from the target
environment and because I want to restore using a database
superuser, which we only allow through a local ident connection.
It would take a pretty big performance difference to overcome the
operational motivations for running on the target.

Thinking about this a little, though, brought to mind the
performance issues when we were converting from Sybase to PostgreSQL
using a home-grown Java conversion utility.  We found best
performance running it on the target for that.  We also got a rather
large performance boost by reading on one thread and writing on
another -- even a 50 row queue to decouple the threads yielded a
very large benefit.  I've heard that we have a big bottleneck in
parsing the input during a restore; I suspect that this alternates
with disk I/O as a bottleneck.  I know multi-threading is always
controversial, but I wonder whether there wouldn't be some way to
decouple the parsing during a COPY FROM from the tuple insert, to
keep two cores busy on the target even during a piped conversion
like this.

-Kevin

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