From: | Thomas Lockhart <lockhart(at)fourpalms(dot)org> |
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To: | mlw <markw(at)mohawksoft(dot)com> |
Cc: | Justin Clift <justin(at)postgresql(dot)org>, Haroldo Stenger <hstenger(at)adinet(dot)com(dot)uy>, "Marc G(dot) Fournier" <scrappy(at)hub(dot)org>, pgsql-hackers(at)postgresql(dot)org, Peter Eisentraut <peter_e(at)gmx(dot)net>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Subject: | Re: Threaded PosgreSQL server |
Date: | 2002-02-07 17:22:56 |
Message-ID: | 3C62B7F0.F93B9803@fourpalms.org |
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Lists: | pgsql-hackers |
...
> As I have said before, multithreading queries within a connection
> process would be pretty cool, on a low load server, this could make a
> big performance increase, but it may be easier to create a couple I/O
> threads per connection process and devise some queuing mechanism for
> disk reads/write. In essence provide an asynchronous I/O system. This
> would give you the some of the performance of multithreading a query,
> while not requiring a complete thread-safe implementation.
The other use case would be a high load server with only one or a few
connections (big queries, few clients); see below.
> I think threading connections is a VERY bad idea. I am dubious that the
> amount of work will result in a decent return on investment.
Agreed. A subset area which *might* be a benefit for the use case above
is to allow threading of subqueries, which might happen after the
optimizer section of code. That is a (pretty big) fraction of the code,
not all of it, and it would still continue the benefits of the
process-per-client model while allowing a client to spread across
multiple processors.
The other area which could be exploited with restructuring to allow
post-optimizer threading is distributed databases, where each of those
subqueries could be rerouted to another server.
A first cut would be to allow read-only distributed databases; that
might demote the nomenclature for this to federated databases, but it is
still an interesting capability.
- Thomas
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