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

["Michael Stack (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HBASE-21879?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Michael Stack updated HBASE-21879:
----------------------------------
    Release Note: 
Before this issue, we've made the read path 100% offheap when block is in the BucketCache but if a cache miss, then the RS needs to read the block via an on-heap API which would causes high young-GC pressure.

This issue adds reading the block via offheap even if reading the block from filesystem directly.  It requires hadoop version(>=2.9.3) but can also work with older hadoop versions (all works but we continue to read block onheap). We have written a careful doc about the implementation, performance and practice here: https://docs.google.com/document/d/1xSy9axGxafoH-Qc17zbD2Bd--rWjjI00xTWQZ8ZwI_E/edit#heading=h.nch5d72p27ex

  was:
Before this issue, we've made the read path 100% offheap when block hit the BucketCache 100%, but if the cache missed then RS need to read the block by on-heap API, which would cause high young GC pressure.
This issue will read the block by offheap even if reading the block from filesystem directly, it have some requirement for hadoop version(>=2.9.3) but can also works with older hadoop version(means still works fine but will read block onheap). We have written a careful doc about the implementation, performance and practice here: https://docs.google.com/document/d/1xSy9axGxafoH-Qc17zbD2Bd--rWjjI00xTWQZ8ZwI_E/edit#heading=h.nch5d72p27ex, for more details please read it.


> 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-alpha-1, 2.3.0
>
>         Attachments: HBASE-21879.v1.patch, HBASE-21879.v1.patch, 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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