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https://issues.apache.org/jira/browse/HBASE-21879?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Zheng Hu updated HBASE-21879:
-----------------------------
Release Note:
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, 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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