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From Yang <teddyyyy...@gmail.com>
Subject Re: StorageService.requestGC() ?
Date Thu, 29 Sep 2011 19:03:41 GMT
I thought the need for GC was based on the code that sstables
deletions are tracked through weak/phantom references.
now I see that sstable is deleted in SStableReader.ReleaseReferences()
---> SegmentedFile.cleanup(),
if this is true, is GC still necessary?

Thanks
Yang

On Thu, Sep 29, 2011 at 11:50 AM, Jonathan Ellis <jbellis@gmail.com> wrote:
> 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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