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From: Tobias Oberstein <tobias.oberstein@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers@postgresql.org
Subject: Re: lseek/read/write overhead becomes visible at scale ..
Date: Wed, 25 Jan 2017 22:27:40 +0100
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Hi,

>> Synthetic PG workload or real world production workload?
>
> Both might work, production-like has bigger pull, but I'd guess
> synthetic is good enough.

Thanks! The box should get PostgreSQL in the not too distant future. 
It'll get a backup from prod, but will act as new prod, so it might take 
some time until a job can be run and a profile collected.

>> So how would I do a perf profile that would be acceptable as prove?
>
> You'd have to look at cpu time, not number of syscalls.  IIRC I
> suggested doing a cycles profile with -g and then using "perf report
> --children" to see how many cycles are spent somewhere below lseek.

Understood. Either profile manually or expand the function.

> I'd also suggest sharing a profile cycles profile, it's quite likely
> that the overhead is completely elsewhere.

Yeah, could be. It'll be interesting to see for sure. I should get a 
chance to collect such profile and then I'll post it back here -

/Tobias



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