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Searching on this more, I find <A HREF="http://www.westnet.com/~gsmith/content/linux-pdflush.htm">http://www.westnet.com/~gsmith/content/linux-pdflush.htm</A> <BR>
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How is this for a working hypothesis: <BR>
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Old Dell servers were 8GB, and I think our DB buffering might have used 2GB of that. <BR>
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New Dell servers are 24GB, and Progress OpenEdge is 64 bit, and uses a good bit more buffer space. <BR>
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<B>/proc/sys/vm/dirty_background_ratio</B> is the same 10%, but that's 3X the amount of dirty accumulated. <BR>
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According to /proc/meminfo, I've seen Dirty: over 3013kB. <BR>
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It would seem that dropping <B>/proc/sys/vm/dirty_background_ratio</B> to 6% might be worth a stab to see if it evens out the peak sync times. It's not that the system is slow, it's just when we bust through a 3 second SLA the client goes bat-crazy. <BR>
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On Tue, 2014-01-21 at 20:57 -0500, Neal Rhodes wrote:<BR>
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So, the context is a pair of new Dell 24 core servers installed this year, running 2.6.32-431.1.2.0.1.el6.x86_64. <BR>
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This replaced older Dell servers running I don't remember what. <BR>
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Both old and new servers ran about 200,000 web service queries a day using Tomcat6 and Progress OpenEdge. <BR>
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The new servers, while faster at DB updates, will several times a month, usually during prime high volumes in early afternoon, exhibit a period of 3 seconds of all DB updates being frozen. When we've chased it down, it seems the DB has completed a checkpoint, and issued a sync call afterwards, and that freezes everyone until it completes. <BR>
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The older servers, while not as fast, didn't exhibit this behavior. <BR>
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I may be wrong about the sync being the culprit; that's what the timings in the DB logs seem to indicate. <BR>
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Is there any tuning parameters which would affect the amount of time for a sync to complete on a busy server? <BR>
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Neal Rhodes<BR>
MNOP Ltd. <BR>
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