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https://issues.apache.org/jira/browse/HBASE-16891?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15614990#comment-15614990
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Anoop Sam John commented on HBASE-16891:
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In AsyncFSOutputHelper
{code}
@Override
188 public void writeInt(int i) {
189 write(Ints.toByteArray(i));
190 }
191
192 @Override
193 public void write(ByteBuffer bb) {
194 byte[] dst = new byte[bb.remaining()];
195 bb.get(dst);
196 write(dst);
197 }
{code}
U can just create the 'out' here as
org.apache.hadoop.hbase.io.ByteArrayOutputStream object and then u can just
delegate the call to this.out
I mean here
{code}
return new AsyncFSOutput() {
private final ByteArrayOutputStream out = new ByteArrayOutputStream();
{code}
Else LGTM
Ya we can not avoid the BB duplicate call as netty ByteBuff do not accept any
offset pos and length. It will be bit strange to accept those with a BB on
which one can set position and length. We did that to avoid garbage.
> Try copying to the Netty ByteBuf directly from the WALEdit
> ----------------------------------------------------------
>
> Key: HBASE-16891
> URL: https://issues.apache.org/jira/browse/HBASE-16891
> Project: HBase
> Issue Type: Sub-task
> Components: wal
> Affects Versions: 2.0.0
> Reporter: ramkrishna.s.vasudevan
> Assignee: ramkrishna.s.vasudevan
> Fix For: 2.0.0
>
> Attachments: HBASE-16891-v1.patch, HBASE-16891-v2.patch,
> HBASE-16891.patch
>
>
> -> The FanOutOneBlockAsyncDFSOutput is a much sophisticated dfs client model
> that works with Netty ByteBuf. Here we hold on connection to the datanodes
> using
> Netty Channels. And the idea is to write data direclty to these channels.
> AsyncHLog gets an append call. The AysncWAL uses the HBase's
> ByteArrayOutputSTream and so the content of the cell is written to this BAOS
> and that is again
> copied to the netty Bytebuf in the FanOutOneBlockAsyncDFSOutput.
> So when the sync call happens this FanoutDFSoutput does the checksum
> calcualtion itself and then writes the content of this buffer direclty to the
> DN channel.
> -> In case of FSHLOg this is different. When an append call comes we direclty
> write the content to the FSDataOutputStream (it is copied to this stream).
> Then here internally there is a checkSum calculation that happens. when a
> sync call happens there is noth ing to do except to notify the NN to flush
> the latest
> data.
> AS we can see from the above that there are two copies in AsyncWAL
> -> From the Cell to the BAOS
> -> From the BAOS to the Netty byte buf
> -> On sync() call, do check sum and finally flush the netty byte buf to the
> DN channel
> In case of FSHLog
> -> From cell to the FSDataoutputstream. data is copied. Check sum happens
> here.
> -> Sync call just tries to notify the NN.
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