From: | Alfred Perlstein <alfred(at)freebsd(dot)org> |
---|---|
To: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
Cc: | Andrew Dunstan <andrew(at)dunslane(dot)net>, Magnus Hagander <magnus(at)hagander(dot)net>, Andres Freund <andres(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Palle Girgensohn <girgen(at)freebsd(dot)org>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com>, Francois Tigeot <ftigeot(at)wolfpond(dot)org> |
Subject: | Re: Perfomance degradation 9.3 (vs 9.2) for FreeBSD |
Date: | 2014-04-21 17:41:25 |
Message-ID: | 53555845.6010601@freebsd.org |
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Lists: | pgsql-hackers |
On 4/21/14, 9:52 AM, Alvaro Herrera wrote:
> Alfred Perlstein wrote:
>
>> I am unsure of the true overhead of making this a runtime tunable so
>> pardon if I'm asking for "a lot". From the perspective of both an
>> OS developer and postgresql user (I am both) it really makes more
>> sense to have it a runtime tunable for the following reasons:
>>
>> From an OS developer making this a runtime allows us to much more
>> easily do the testing (instead of needing two compiled versions).
>> From a sysadmin perspective it makes switching to/from a LOT easier
>> in case the new mmap code exposes a stability or performance bug.
> In this case, AFAICS the only overhead of a runtime option (what we call
> a GUC) is the added potential for user confusion, and the necessary
> documentation. If we instead go for a compile-time option, both items
> become smaller.
>
> In any case, I don't see that there's much need for a runtime option,
> really; you already know that the mmap code path is slower in FreeBSD.
> You only need to benchmark both options once the FreeBSD vm code itself
> is fixed, right?
>
> In fact, it might not even need to be a configure option; I would
> suggest a pg_config_manual.h setting instead, and perhaps tweaks to the
> src/template/freebsd file to enable it automatically on the "broken"
> FreeBSD releases. We could then, in the future, have the template
> itself turn the option off for the future FreeBSD release that fixes the
> problem.
>
That is correct, until you're in prod and suddenly one option becomes
unstable, or you want to try a quick kernel patch without rebooting.
Look, this is an argument I've lost time and time again in open source
software communities, the idea of a software option as opposed to
compile time really seems to hit people the wrong way.
I think from now on it just makes sense to sit back and let whatever
happens happen.
-Alfred
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