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https://issues.apache.org/jira/browse/HBASE-16891?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15614811#comment-15614811
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Anoop Sam John commented on HBASE-16891:
----------------------------------------
U can see in EnsureKvEncoder
{code}
public void write(Cell cell) throws IOException {
checkFlushed();
// Make sure to write tags into WAL
ByteBufferUtils.putInt(this.out, KeyValueUtil.getSerializedSize(cell,
true));
KeyValueUtil.oswrite(cell, this.out, true);
}
{code}
KVUtil#oswrite
{code}
public static int oswrite(final Cell cell, final OutputStream out, final
boolean withTags)
throws IOException {
if (cell instanceof ExtendedCell) {
return ((ExtendedCell)cell).write(out, withTags);
} else {
..
{code}
All our cells in server side will be ExtendedCell type.
Pls see OffheapKeyValue
{code}
public int write(OutputStream out, boolean withTags) throws IOException {
int length = getSerializedSize(withTags);
ByteBufferUtils.copyBufferToStream(out, this.buf, this.offset, length);
return length;
}
{code}
And then BBUtil
{code}
public static void copyBufferToStream(OutputStream out, ByteBuffer in,
int offset, int length) throws IOException {
if (out instanceof ByteBufferSupportOutputStream) {
((ByteBufferSupportOutputStream) out).write(in, offset, length);
} else if (in.hasArray()) {
out.write(in.array(), in.arrayOffset() + offset, length);
} else {
for (int i = 0; i < length; ++i) {
out.write(toByte(in, offset + i));
}
}
}
{code}
So ya in Encoders we have OutputSTream type only.. Here in this util there is a
type check and we avoid on heap copy from DBB.
> 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.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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