[jira] [Commented] (HBASE-15180) Reduce garbage created while reading Cells from Codec Decoder

["Anoop Sam John (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-15180?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15173243#comment-15173243 ] 

Anoop Sam John commented on HBASE-15180:
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So in this patch made sure that on client side we wont go with optimization of Cells created directly over the response read buffer.   The cells will be handed over to user app and we can not be sure whether some of the cells will be cached or not.  Caching even single cell will make it such that we can not GC the bigger sized response buffer.  Server side we have MSLAB and copy to that before adding Cells to memstore.  [~enis]  Ping for ur review as well.

> Reduce garbage created while reading Cells from Codec Decoder
> -------------------------------------------------------------
>
>                 Key: HBASE-15180
>                 URL: https://issues.apache.org/jira/browse/HBASE-15180
>             Project: HBase
>          Issue Type: Sub-task
>          Components: regionserver
>    Affects Versions: 0.98.0
>            Reporter: Anoop Sam John
>            Assignee: Anoop Sam John
>             Fix For: 2.0.0
>
>         Attachments: HBASE-15180.patch, HBASE-15180_V2.patch, HBASE-15180_V4.patch, HBASE-15180_V6.patch, HBASE-15180_V7.patch
>
>
> In KeyValueDecoder#parseCell (Default Codec decoder) we use KeyValueUtil#iscreate to read cells from the InputStream. Here we 1st create a byte[] of length 4 and read the cell length and then an array of Cell's length and read in cell bytes into it and create a KV.
> Actually in server we read the reqs into a byte[] and CellScanner is created on top of a ByteArrayInputStream on top of this. By default in write path, we have MSLAB usage ON. So while adding Cells to memstore, we will copy the Cell bytes to MSLAB memory chunks (default 2 MB size) and recreate Cells over that bytes.  So there is no issue if we create Cells over the RPC read byte[] directly here in Decoder.  No need for 2 byte[] creation and copy for every Cell in request.
> My plan is to make a Cell aware ByteArrayInputStream which can read Cells directly from it.  
> Same Codec path is used in client side also. There better we can avoid this direct Cell create and continue to do the copy to smaller byte[]s path.  Plan to introduce some thing like a CodecContext associated with every Codec instance which can say the server/client context.



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