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Re: Shared buffers, db transactions commited, and write IO on Solaris

From: Josh Berkus <josh(at)agliodbs(dot)com>
To: Erik Jones <erik(at)myemma(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: Shared buffers, db transactions commited, and write IO on Solaris
Date: 2007-03-30 21:46:35
Message-ID: 200703301446.35858.josh@agliodbs.com (view raw or flat)
Thread:
Lists: pgsql-performance
Erik,

> You'er welcome!  However, I believe our situation is very different
> from what you're testing if I understand you correctly.  Are you
> saying that you're entire database will fit in memory?  If so, then
> these are very different situations as there is no way ours could
> ever do that.  In fact, I'm not sure that forcedirectio would really
> net you any gain in that situation as the IO service time will be
> basically nil if the filesystem cache doesn't have to page which I
> would think is why your seeing what you are.

Even more interesting.  I guess we've been doing too much work with 
benchmark workloads, which tend to be smaller databases.  

Thing is, there's *always* I/O for a read/write database.  If nothing else, 
updates have to be synched to disk.

Anyway ... regarding the mystery transactions ... are you certain that it's 
not your application?  I can imagine that, if your app has a fairly tight 
retry interval for database non-response, that I/O sluggishness could 
result in commit attempts spinning out of control.

-- 
--Josh

Josh Berkus
PostgreSQL @ Sun
San Francisco

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