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https://issues.apache.org/jira/browse/HBASE-7404?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13804386#comment-13804386
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Lars Hofhansl commented on HBASE-7404:
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Was waiting for HBASE-8894, but it seems that has some ways to go.
The problem with this patch is that when you enable the off-heap bucketcache
the blockcache is disabled for all but the index blocks. There is no
in-between. So from that angle it is not very useful, because most folks
couldn't just switch it on, since it is quite a bit slower than the blockcache.
If it would be configurable per table/cf that would be another story. One could
then have smaller, hot table still use the blockcache and have larger
not-so-tables use the offheap cache; and thus we'd be able to make use of RAM
sizes of 128gb or more.
At the same time, since this is all new code, I'm fine with reviewing Dave's
backport a bit more and then committing it.
Comments?
> Bucket Cache:A solution about CMS,Heap Fragment and Big Cache on HBASE
> ----------------------------------------------------------------------
>
> Key: HBASE-7404
> URL: https://issues.apache.org/jira/browse/HBASE-7404
> Project: HBase
> Issue Type: New Feature
> Affects Versions: 0.94.3
> Reporter: chunhui shen
> Assignee: chunhui shen
> Fix For: 0.95.0
>
> Attachments: 7404-0.94-fixed-lines.txt, 7404-trunk-v10.patch,
> 7404-trunk-v11.patch, 7404-trunk-v12.patch, 7404-trunk-v13.patch,
> 7404-trunk-v13.txt, 7404-trunk-v14.patch, BucketCache.pdf,
> hbase-7404-94v2.patch, HBASE-7404-backport-0.94.patch,
> hbase-7404-trunkv2.patch, hbase-7404-trunkv9.patch, Introduction of Bucket
> Cache.pdf
>
>
> First, thanks @neil from Fusion-IO share the source code.
> Usage:
> 1.Use bucket cache as main memory cache, configured as the following:
> –"hbase.bucketcache.ioengine" "heap"
> –"hbase.bucketcache.size" 0.4 (size for bucket cache, 0.4 is a percentage of
> max heap size)
> 2.Use bucket cache as a secondary cache, configured as the following:
> –"hbase.bucketcache.ioengine" "file:/disk1/hbase/cache.data"(The file path
> where to store the block data)
> –"hbase.bucketcache.size" 1024 (size for bucket cache, unit is MB, so 1024
> means 1GB)
> –"hbase.bucketcache.combinedcache.enabled" false (default value being true)
> See more configurations from org.apache.hadoop.hbase.io.hfile.CacheConfig and
> org.apache.hadoop.hbase.io.hfile.bucket.BucketCache
> What's Bucket Cache?
> It could greatly decrease CMS and heap fragment by GC
> It support a large cache space for High Read Performance by using high speed
> disk like Fusion-io
> 1.An implementation of block cache like LruBlockCache
> 2.Self manage blocks' storage position through Bucket Allocator
> 3.The cached blocks could be stored in the memory or file system
> 4.Bucket Cache could be used as a mainly block cache(see CombinedBlockCache),
> combined with LruBlockCache to decrease CMS and fragment by GC.
> 5.BucketCache also could be used as a secondary cache(e.g. using Fusionio to
> store block) to enlarge cache space
> How about SlabCache?
> We have studied and test SlabCache first, but the result is bad, because:
> 1.SlabCache use SingleSizeCache, its use ratio of memory is low because kinds
> of block size, especially using DataBlockEncoding
> 2.SlabCache is uesd in DoubleBlockCache, block is cached both in SlabCache
> and LruBlockCache, put the block to LruBlockCache again if hit in SlabCache ,
> it causes CMS and heap fragment don't get any better
> 3.Direct heap performance is not good as heap, and maybe cause OOM, so we
> recommend using "heap" engine
> See more in the attachment and in the patch
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