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https://issues.apache.org/jira/browse/HBASE-15788?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15664692#comment-15664692
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stack commented on HBASE-15788:
-------------------------------
The writeInt doesn't belong in the new BBWriter Interface being a perf
improvement only. Suggested adding a note stating this and then +1 again on
commit. Thanks.
> Use Offheap ByteBuffers from BufferPool to read RPC requests.
> -------------------------------------------------------------
>
> Key: HBASE-15788
> URL: https://issues.apache.org/jira/browse/HBASE-15788
> Project: HBase
> Issue Type: Sub-task
> Components: regionserver
> Reporter: ramkrishna.s.vasudevan
> Assignee: Anoop Sam John
> Fix For: 2.0.0
>
> Attachments: HBASE-15788.patch, HBASE-15788_V10.patch,
> HBASE-15788_V4.patch, HBASE-15788_V5.patch, HBASE-15788_V6.patch,
> HBASE-15788_V7.patch, HBASE-15788_V8.patch, HBASE-15788_v9.patch
>
>
> Right now, when an RPC request reaches RpcServer, we read the request into an
> on demand created byte[]. When it is write request and including many
> mutations, the request size will be some what larger and we end up creating
> many temp on heap byte[] and causing more GCs.
> We have a ByteBufferPool of fixed sized off heap BBs. This is used at
> RpcServer while sending read response only. We can make use of the same while
> reading reqs also. Instead of reading whole of the request bytes into a
> single BB, we can read into N BBs (based on the req size). When BB is not
> available from pool, we will fall back to old way of on demand on heap byte[]
> creation.
> Remember these are off heap BBs. We read many proto objects from this read
> request bytes (like header, Mutation protos etc). Thanks to PB 3 and our
> shading work as it supports off heap BB now. Also the payload cells are also
> in these DBBs now. The codec decoder can work on these and create off heap
> BBs. Whole of our write path work with Cells now. At the time of addition to
> memstore, these cells are by default copied to MSLAB ( off heap based pooled
> MSLAB issue to follow this one). If MSLAB copy is not possible, we will do a
> copy to on heap byte[].
> One possible down side of this is :
> Before adding to Memstore, we do write to WAL. So the Cells created out of
> the offheap BBs (Codec#Decoder) will be used to write to WAL. The default
> FSHLog works with an OS obtained from DFSClient. This will have only standard
> OS write APIs which is byte[] based. So just to write to WAL, we will end up
> in temp on heap copy for each of the Cell. The other WAL imp (ie. AsynWAL)
> supports writing offheap Cells directly. We have work in progress to make
> AsycnWAL as default. Also we can raise HDFS req to support BB based write
> APIs in their client OS? Until then, will try for a temp workaround solution.
> Patch to say more on this.
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