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Re: Parallel (concurrent) inserts?

From: Ivan Voras <ivoras(at)freebsd(dot)org>
To: Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Parallel (concurrent) inserts?
Date: 2012-05-25 23:56:57
Message-ID: CAF-QHFWALNOmSj_+EVbdRc=e5kai5ckRL7P2153SzmkcPO=u-w@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On 26 May 2012 01:36, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
> On Fri, May 25, 2012 at 3:04 PM, Ivan Voras <ivoras(at)freebsd(dot)org> wrote:
>> Hello,
>>
>> I'm wondering if there is ia document describing which guarantees (if
>> any) PostgreSQL makes about concurrency for various operations? Speaking
>> in general (i.e. IO can handle it, number of CPU cores and client
>> threads is optimal), are fully concurrent operations (independant and
>> non-blocking) possible for:
>
> By "fully concurrent" do you mean that there is no detectable
> sub-linear scaling at all?  I'm pretty sure that no such guarantees
> can be made.

> For concurrent bulk loads, there was severe contention on generating
> WAL between concurrent bulk loaders.  That is greatly improved in the
> upcoming 9.2 release.

I was thinking about major exclusive locks in the code paths which
would block multiple clients operating on unrelated data (the same
questions go for update operations). For example: if the free space
map or whole index trees are exclusively locked, things like that. The
WAL issue you mention seems exactly like what I was asking about, but
are there any others?

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