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https://issues.apache.org/jira/browse/HBASE-16287?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15395150#comment-15395150
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Yu Li commented on HBASE-16287:
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bq. Why -1g? We calc the BC size by conf xmx value * BC percentage.
Not actually... In CacheConfig#instantiateBlockCache, we use
{{ManagementFactory.getMemoryMXBean().getHeapMemoryUsage()}} as the base, and
JVM will return {{Xmx-survivorSize}} for this. We could also confirm this from
the TRACE log: "totalSize=15.29 GB, freeSize=-5.99 GB, max=9.30 GB"
bq. Why the eviction thread is so slow?
It's possible that the loading speed is higher than eviction in some cases like
with PCIe SSD, according to our observation.
bq. The keypoint is "hard capacity limit". We need a buffer, 1.2x is good
Yep, that's why I suggest to attache the patch, codes are easier to read than
words for us, I guess. :-)
> 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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