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POReducing JVM pause time > 1 second using UseConcMarkSweepGC
 

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  1. POReducing JVM pause time > 1 second using UseConcMarkSweepGC
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    <p>I'm running a memory intensive app on a machine with 16Gb of RAM, and an 8-core processor, and Java 1.6 all running on CentOS release 5.2 (Final). Exact JVM details are:</p> <pre><code>java version "1.6.0_10" Java(TM) SE Runtime Environment (build 1.6.0_10-b33) Java HotSpot(TM) 64-Bit Server VM (build 11.0-b15, mixed mode) </code></pre> <p>I'm launching the app with the following command line options:</p> <pre><code>java -XX:+UseConcMarkSweepGC -verbose:gc -server -Xmx10g -Xms10g ... </code></pre> <p>My application exposes a JSON-RPC API, and my goal is to respond to requests within 25ms. Unfortunately, I'm seeing delays up to and exceeding 1 second and it appears to be caused by garbage collection. Here are some of the longer examples:</p> <pre><code>[GC 4592788K-&gt;4462162K(10468736K), 1.3606660 secs] [GC 5881547K-&gt;5768559K(10468736K), 1.2559860 secs] [GC 6045823K-&gt;5914115K(10468736K), 1.3250050 secs] </code></pre> <p>Each of these garbage collection events was accompanied by a delayed API response of very similar duration to the length of the garbage collection shown (to within a few ms).</p> <p>Here are some typical examples (these were all produced within a few seconds):</p> <pre><code>[GC 3373764K-&gt;3336654K(10468736K), 0.6677560 secs] [GC 3472974K-&gt;3427592K(10468736K), 0.5059650 secs] [GC 3563912K-&gt;3517273K(10468736K), 0.6844440 secs] [GC 3622292K-&gt;3589011K(10468736K), 0.4528480 secs] </code></pre> <p>The thing is that I thought the UseConcMarkSweepGC would avoid this, or at least make it extremely rare. On the contrary, delays exceeding 100ms are occurring almost once a minute or more (although delays of over 1 second are considerably rarer, perhaps once every 10 or 15 minutes).</p> <p>The other thing is that I thought only a FULL GC would cause threads to be paused, yet these don't appear to be full GCs.</p> <p>It may be relevant to note that most of the memory is occupied by a LRU memory cache that makes use of soft references.</p> <p>Any assistance or advice would be greatly appreciated.</p>
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    1. COWhat JDK/JRE and what OS?
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    2. COSorry, just added that info
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