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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: StorageService.requestGC() ?
Date Thu, 29 Sep 2011 18:50:12 GMT
As the comment says,
            // retry after GCing to force unmap of compacted SSTables
so they can be deleted

See also http://wiki.apache.org/cassandra/MemtableSSTable

Note that this has changed in 1.0:
https://issues.apache.org/jira/browse/CASSANDRA-2521

On Thu, Sep 29, 2011 at 1:14 PM, Yang <teddyyyy123@gmail.com> wrote:
> Table.getDataFileLocation() calls StorageService.requestGC(), which
> calls System.gc()
>
> I think I saw one GC in my log due to this code, and it caused a JVM
> freeze for 14 seconds.
> why do we need to call explicit GC ?
>
> thanks
> Yang
>
>
>
> [Times: user=2.81 sys=0.00, real=0.46 secs]
> 3472.943: [GC 3472.943: [ParNew: 21339139K->326984K(23592960K),
> 0.4742050 secs] 30764101K->10032251K(49807360K), 0.4743710 secs]
> [Times: user=2.91 sys=0.01, real=0.47 secs]
> 3519.043: [GC 3519.043: [ParNew: 21298504K->386099K(23592960K),
> 0.5201430 secs] 31003771K->10363088K(49807360K), 0.5203120 secs]
> [Times: user=3.15 sys=0.03, real=0.52 secs]
> 3560.277: [GC 3560.278: [ParNew: 21357619K->434850K(23592960K),
> 0.4693880 secs] 31334608K->10676370K(49807360K), 0.4695450 secs]
> [Times: user=2.92 sys=0.00, real=0.47 secs]
> 3601.343: [Full GC (System) 3601.343: [CMS:
> 10241519K->3496676K(26214400K), 14.6823750 secs]
> 28763882K->3496676K(49807360K), [CMS Perm : 27683K->27623K(27776K)],
> 14.6900120 secs] [Times: user=14.73 sys=0.00, real=14.69 secs]
> 3665.223: [GC 3665.224: [ParNew: 20971520K->361802K(23592960K),
> 0.2379040 secs] 24468196K->3858479K(49807360K), 0.2380660 secs]
> [Times: user=1.57 sys=0.01, real=0.23 secs]
> 3704.967: [GC 3704.968: [ParNew: 21333322K->359503K(23592960K),
> 0.4433910 secs] 24829999K->4173314K(49807360K), 0.4435500 secs]
> [Times: user=2.72 sys=0.02, real=0.44 secs]
> 3801.962: [GC 3801.962: [ParNew: 21331023K->388609K(23592960K),
> 0.5236180 secs] 25144834K->4479343K(49807360K), 0.5238240 secs]
> [Times: user=3.42 sys=0.00, real=0.53 secs]
>



-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of DataStax, the source for professional Cassandra support
http://www.datastax.com

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