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Date: Thu, 08 Jan 2015 21:53:42 -0700
From: Shawn Heisey <apache@elyograg.org>
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Subject: GC tuning question - can improving GC pauses cause indexing to slow
 down?
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Is it possible that tuning garbage collection to achieve much better
pause characteristics might actually *decrease* index performance?

Rebuilds that I did while still using a tuned CMS config would take
between 5.5 and 6 hours, sometimes going slightly over 6 hours.

A rebuild that I did recently with G1 took 6.82 hours.  A rebuild that I
did yesterday with further tuned G1 settings (which seemed to result in
much smaller pauses than the previous G1 settings) took 8.97 hours, and
that was on slightly faster hardware than the rebuild that took 6.82 hours.

These rebuilds are done with DIH from MySQL.

It seems completely counter-intuitive that settings which show better GC
pause characteristics would result in indexing performance going down
... so can anyone shed light on this, tell me whether I'm out of my mind?

Thanks,
Shawn