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https://issues.apache.org/jira/browse/HBASE-16287?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15395123#comment-15395123
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Anoop Sam John commented on HBASE-16287:
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No we can not do size check before putting block to cache and reject new cache
requests. Then it wont be LRU in nature any more. The current way of Eviction
thread doing the work is correct only. Though agree to the point that when this
thread is slow, we might grow much big in size ! So the proposed way of some
safe check seems reasonable.
bq.(32g-1g)*0.3=9.3g.
Why -1g? We calc the BC size by conf xmx value * BC percentage.
Why the eviction thread is so slow?
> BlockCache size should not exceed acceptableSize too many
> ---------------------------------------------------------
>
> Key: HBASE-16287
> URL: https://issues.apache.org/jira/browse/HBASE-16287
> Project: HBase
> Issue Type: Improvement
> Components: BlockCache
> Reporter: Yu Sun
>
> Our regionserver has a configuation as bellow：
> -Xmn4g -Xms32g -Xmx32g -XX:SurvriorRatio=2 -XX:+UseConcMarkSweepGC
> also we only use blockcache,and set hfile.block.cache.size = 0.3 in
> hbase_site.xml,so under this configuration, the lru block cache size will
> be(32g-1g)*0.3=9.3g. but in some scenarios，some of the rs will occur
> continuous FullGC for hours and most importantly, after FullGC most of the
> object in old will not be GCed. so we dump the heap and analyse with MAT and
> we observed a obvious memory leak in LruBlockCache, which occpy about 16g
> memory, then we set set class LruBlockCache log level to TRACE and observed
> this in log:
> {quote}
> 2016-07-22 12:17:58,158 INFO [LruBlockCacheStatsExecutor]
> hfile.LruBlockCache: totalSize=15.29 GB, freeSize=-5.99 GB, max=9.30 GB,
> blockCount=628182, accesses=101799469125, hits=93517800259, hitRatio=91.86%,
> , cachingAccesses=99462650031, cachingHits=93468334621,
> cachingHitsRatio=93.97%, evictions=238199, evicted=4776350518,
> evictedPerRun=20051.93359375{quote}
> we can see blockcache size has exceeded acceptableSize too many, which will
> cause the FullGC more seriously.
> Afterfter some investigations, I found in this function:
> {code:borderStyle=solid}
> public void cacheBlock(BlockCacheKey cacheKey, Cacheable buf, boolean
> inMemory,
> final boolean cacheDataInL1) {
> {code}
> No matter the blockcache size has been used, just put the block into it. but
> if the evict thread is not fast enough, blockcache size will increament
> significantly.
> So here I think we should have a check, for example, if the blockcache size >
> 1.2 * acceptableSize(), just return and dont put into it until the blockcache
> size if under watrmark. if this is reasonable, I can make a small patch for
> this.
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