Message-ID: <55E75A5C.2090409@dalibo.com>
Date: Wed, 02 Sep 2015 22:21:48 +0200
From: Julien Rouhaud <julien.rouhaud@dalibo.com>
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To: Andres Freund <andres@anarazel.de>
CC: Jeff Janes <jeff.janes@gmail.com>, Bruce Momjian <bruce@momjian.us>,
 Merlin Moncure <mmoncure@gmail.com>,
 "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: Allow a per-tablespace effective_io_concurrency setting
References: 
 <CAHyXU0yaUG9R_E5=1gdXhD-MpWR=Gr=4=EHFD_fRid2+SCQrqA@mail.gmail.com>
 <CAHyXU0yiVvfQAnR9cyH=HWh1WbLRsioe=mzRJTHwtr=2azsTdQ@mail.gmail.com>
 <20141206130828.GA1314@momjian.us>
 <CAHyXU0wgpE2E3B+rmZ959tJT_adPFfPvHNqeA9K9mkJRAT9HXw@mail.gmail.com>
 <20141209204337.GC24488@momjian.us>
 <CAMkU=1w0nXDcwhyQurh+XCdQ2AyeSLBcMGqrNAYsckLbTqq3mw@mail.gmail.com>
 <55AA2469.20306@dalibo.com> <55AA27C3.7060009@dalibo.com>
 <20150902135351.GA5286@alap3.anarazel.de>
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On 02/09/2015 15:53, Andres Freund wrote:
> On 2015-07-18 12:17:39 +0200, Julien Rouhaud wrote:
> 
> You also didn't touch /* * How many buffers PrefetchBuffer callers
> should try to stay ahead of their * ReadBuffer calls by.  This is
> maintained by the assign hook for * effective_io_concurrency.  Zero
> means "never prefetch". */ int			target_prefetch_pages = 0; which
> surely doesn't make sense anymore after these changes.
> 
> But do we even need that variable now?
> 

I thought this was related to the effective_io_concurrency GUC
(possibly overloaded by the per-tablespace setting), so I didn't make
any change on that.

I also just found an issue with my previous patch, the global
effective_io_concurrency GUC was ignored if the tablespace had a
specific seq_page_cost or random_page_cost setting, I just fixed that
in my local branch.


>> diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h 
>> index dc167f9..57008fc 100644 --- a/src/include/utils/guc.h +++
>> b/src/include/utils/guc.h @@ -26,6 +26,9 @@ #define MAX_KILOBYTES
>> (INT_MAX / 1024) #endif
>> 
>> +/* upper limit for effective_io_concurrency */ +#define
>> MAX_IO_CONCURRENCY 1000 + /* * Automatic configuration file name
>> for ALTER SYSTEM. * This file will be used to store values of
>> configuration parameters @@ -256,6 +259,8 @@ extern int
>> temp_file_limit;
>> 
>> extern int	num_temp_buffers;
>> 
>> +extern int	effective_io_concurrency; +
> 
> target_prefetch_pages is declared in bufmgr.h - that seems like a
> better place for these.
> 

I was rather sceptical about that too. I'll move these in bufmgr.h.


Regards.


- -- 
Julien Rouhaud
http://dalibo.com - http://dalibo.org
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