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https://issues.apache.org/jira/browse/HBASE-15180?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15124908#comment-15124908
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Anoop Sam John commented on HBASE-15180:
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bq.Yes, I noticed about 5-10% improvement on GC times and CPU utilization after
disabling MSLAB only if using G1GC. Tuning MSLAB helps a little but I don't see
to much advantage to have it enabled when G1GC is there.
I believe [[email protected]] done some YCSB test with writes (G1GC we
have) and he said it was giving bad results.
bq.MSLAB is like an HBASE-14918 Segment. Would it make sense to make it a
Segment?
Segment is a part of the memstore right? MSLAB is a place for only keeping the
Cell data. So I am not sure whether MSLAB can be a Segment.
Any way our work in this umbrella Jira is to make the write path off heap and
make an off heap MSLAB impl.
> 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
> Reporter: Anoop Sam John
> Assignee: Anoop Sam John
> Fix For: 2.0.0
>
> Attachments: HBASE-15180.patch, HBASE-15180_V2.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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