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https://issues.apache.org/jira/browse/HBASE-27370?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on HBASE-27370 started by Wellington Chevreuil.
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> Avoid decompressing blocks when reading from bucket cache prefetch threads
> ---------------------------------------------------------------------------
>
> Key: HBASE-27370
> URL: https://issues.apache.org/jira/browse/HBASE-27370
> Project: HBase
> Issue Type: Improvement
> Reporter: Wellington Chevreuil
> Assignee: Wellington Chevreuil
> Priority: Major
>
> When prefetching blocks into bucket cache, we had observed a consistent CPU
> usage around 70% with no other workloads ongoing. For large bucket caches
> (i.e. when using file based bucket cache), the prefetch can last for sometime
> and having such a high CPU usage may impact the database usage by client
> applications.
> Further analysis of the prefetch threads stack trace showed that very often,
> decompress logic is being executed by these threads:
> {noformat}
> "hfile-prefetch-1654895061122" #234 daemon prio=5 os_prio=0
> tid=0x0000557bb2907000 nid=0x406d runnable [0x00007f294a504000]
> java.lang.Thread.State: RUNNABLE
> at
> org.apache.hadoop.io.compress.snappy.SnappyDecompressor.decompressBytesDirect(Native
> Method)
> at
> org.apache.hadoop.io.compress.snappy.SnappyDecompressor.decompress(SnappyDecompressor.java:235)
> at
> org.apache.hadoop.io.compress.BlockDecompressorStream.decompress(BlockDecompressorStream.java:88)
> at
> org.apache.hadoop.io.compress.DecompressorStream.read(DecompressorStream.java:105)
> at java.io.BufferedInputStream.read1(BufferedInputStream.java:284)
> at java.io.BufferedInputStream.read(BufferedInputStream.java:345)
> - locked <0x00000002d24c0ae8> (a java.io.BufferedInputStream)
> at
> org.apache.hadoop.hbase.io.util.BlockIOUtils.readFullyWithHeapBuffer(BlockIOUtils.java:105)
> at
> org.apache.hadoop.hbase.io.compress.Compression.decompress(Compression.java:465)
> at
> org.apache.hadoop.hbase.io.encoding.HFileBlockDefaultDecodingContext.prepareDecoding(HFileBlockDefaultDecodingContext.java:90)
> at
> org.apache.hadoop.hbase.io.hfile.HFileBlock.unpack(HFileBlock.java:650)
> at
> org.apache.hadoop.hbase.io.hfile.HFileReaderImpl.readBlock(HFileReaderImpl.java:1342)
> {noformat}
> This is because *HFileReaderImpl.readBlock* is always decompressing blocks
> even when *hbase.block.data.cachecompressed* is set to true.
> This patch proposes an alternative flag to differentiate prefetch from normal
> reads, so that doesn't decompress DATA blocks when prefetching with
> *hbase.block.data.cachecompressed* set to true.
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