[jira] [Commented] (HBASE-21879) Read HFile's block to ByteBuffer directly instead of to byte for reducing young gc purpose

["stack (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-21879?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16766211#comment-16766211 ] 

stack commented on HBASE-21879:
-------------------------------

Sounds really good [~openinx] (What API are you referring to here => "...but 2.7+ has supported this now, so we can fix this now.."). Thanks.

> Read HFile's block to ByteBuffer directly instead of to byte for reducing young gc purpose
> ------------------------------------------------------------------------------------------
>
>                 Key: HBASE-21879
>                 URL: https://issues.apache.org/jira/browse/HBASE-21879
>             Project: HBase
>          Issue Type: Improvement
>            Reporter: Zheng Hu
>            Assignee: Zheng Hu
>            Priority: Major
>             Fix For: 3.0.0, 2.2.0, 2.3.0, 2.1.4
>
>         Attachments: QPS-latencies-before-HBASE-21879.png, gc-data-before-HBASE-21879.png
>
>
> In HFileBlock#readBlockDataInternal,  we have the following: 
> {code}
> @VisibleForTesting
> protected HFileBlock readBlockDataInternal(FSDataInputStream is, long offset,
>     long onDiskSizeWithHeaderL, boolean pread, boolean verifyChecksum, boolean updateMetrics)
>  throws IOException {
>  // .....
>   // TODO: Make this ByteBuffer-based. Will make it easier to go to HDFS with BBPool (offheap).
>   byte [] onDiskBlock = new byte[onDiskSizeWithHeader + hdrSize];
>   int nextBlockOnDiskSize = readAtOffset(is, onDiskBlock, preReadHeaderSize,
>       onDiskSizeWithHeader - preReadHeaderSize, true, offset + preReadHeaderSize, pread);
>   if (headerBuf != null) {
>         // ...
>   }
>   // ...
>  }
> {code}
> In the read path,  we still read the block from hfile to on-heap byte[], then copy the on-heap byte[] to offheap bucket cache asynchronously,  and in my  100% get performance test, I also observed some frequent young gc,  The largest memory footprint in the young gen should be the on-heap block byte[].
> In fact, we can read HFile's block to ByteBuffer directly instead of to byte[] for reducing young gc purpose. we did not implement this before, because no ByteBuffer reading interface in the older HDFS client, but 2.7+ has supported this now,  so we can fix this now. I think. 
> Will provide an patch and some perf-comparison for this. 



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