From: Ivan Voras <ivoras@freebsd.org>
To: pgsql-performance@postgresql.org
Subject: Re: [HACKERS] MIT benchmarks pgsql multicore (up to 48)performance
Date: Thu, 07 Oct 2010 00:31:19 +0200
Message-ID: <i8itbn$kre$1@dough.gmane.org> (raw)
In-Reply-To: <4CAA21C7.1030701@agliodbs.com>
References: <AANLkTimW2UgVPGw6MRUBj9HabvwmsmkZasL3hKv-nUJ2@mail.gmail.com>
<20101004175545.GA2690@csail.mit.edu>
<4CAA21C7.1030701@agliodbs.com>
On 10/04/10 20:49, Josh Berkus wrote:
>> The other major bottleneck they ran into was a kernel one: reading from
>> the heap file requires a couple lseek operations, and Linux acquires a
>> mutex on the inode to do that. The proper place to fix this is
>> certainly in the kernel but it may be possible to work around in
>> Postgres.
>
> Or we could complain to Kernel.org. They've been fairly responsive in
> the past. Too bad this didn't get posted earlier; I just got back from
> LinuxCon.
>
> So you know someone who can speak technically to this issue? I can put
> them in touch with the Linux geeks in charge of that part of the kernel
> code.
Hmmm... lseek? As in "lseek() then read() or write()" idiom? It AFAIK
cannot be fixed since you're modifying the global "strean position"
variable and something has got to lock that.
OTOH, pread() / pwrite() don't have to do that.
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To: pgsql-performance@postgresql.org
Cc: ivoras@freebsd.org
Subject: Re: [HACKERS] MIT benchmarks pgsql multicore (up to 48)performance
In-Reply-To: <i8itbn$kre$1@dough.gmane.org>
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