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From "Lars Hofhansl (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-4496) HFile V2 does not honor setCacheBlocks when scanning.
Date Tue, 27 Sep 2011 18:53:46 GMT

     [ https://issues.apache.org/jira/browse/HBASE-4496?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Lars Hofhansl updated HBASE-4496:

    Attachment: 4496.txt

This fixes the problem for me.

TestHFileBlock, TestCacheOnWrite, TestHFileBlockIndex, and TestHFileWriterV2 still pass.

It's not pretty, though. Lots of places where cacheBlock now needs to be passed around.
I erred on the side of caution, where is wasn't clear whether the block should be cached of
not, I kept it being cached (as before).

Somebody with more knowledge about HFileReaderV2 should have a look. If there's something
nicer to do, please let me know.
It is not clear to be how to write a test for this.
> HFile V2 does not honor setCacheBlocks when scanning.
> -----------------------------------------------------
>                 Key: HBASE-4496
>                 URL: https://issues.apache.org/jira/browse/HBASE-4496
>             Project: HBase
>          Issue Type: Bug
>          Components: regionserver
>    Affects Versions: 0.92.0, 0.94.0
>            Reporter: Lars Hofhansl
>            Assignee: Lars Hofhansl
>             Fix For: 0.92.0, 0.94.0
>         Attachments: 4496.txt
> While testing the LRU cache during the scanning I noticed quite some churn in the cache
even when Scan.cacheBlocks is set to false. After debugging this, I found that HFile V2 always
caches blocks in the LRU cache regardless of the cacheBlocks setting.
> Here's a trace (from Eclipse) showing the problem:
> HFileReaderV2.readBlock(long, int, boolean, boolean, boolean) line: 279	
> HFileReaderV2.readBlockData(long, long, int, boolean) line: 219	
> HFileBlockIndex$BlockIndexReader.seekToDataBlock(byte[], int, int, HFileBlock) line:
> HFileReaderV2$ScannerV2.seekTo(byte[], int, int, boolean) line: 502	
> HFileReaderV2$ScannerV2.reseekTo(byte[], int, int) line: 539	
> StoreFileScanner.reseekAtOrAfter(HFileScanner, KeyValue) line: 151	
> StoreFileScanner.reseek(KeyValue) line: 110	
> KeyValueHeap.reseek(KeyValue) line: 255	
> StoreScanner.reseek(KeyValue) line: 409	
> StoreScanner.next(List<KeyValue>, int) line: 304	
> KeyValueHeap.next(List<KeyValue>, int) line: 114	
> KeyValueHeap.next(List<KeyValue>) line: 143	
> HRegion$RegionScannerImpl.nextRow(byte[]) line: 2774	
> HRegion$RegionScannerImpl.nextInternal(int) line: 2722	
> HRegion$RegionScannerImpl.next(List<KeyValue>, int) line: 2682	
> HRegion$RegionScannerImpl.next(List<KeyValue>) line: 2699	
> HRegionServer.next(long, int) line: 2092	
> Every scanner.next causes a reseek, which eventually causes a call to HFileBlockIndex$BlockIndexReader.seekToDataBlock(...)
at which point the cacheBlocks information is lost. HFileReaderV2.readBlockData calls HFileReaderV2.readBlock
with cacheBlocks set unconditionally to true.
> The fix is not immediately clear, unless we want to pass cacheBlocks to HFileBlockIndex$BlockIndexReader.seekToDataBlock
and then on to HFileBlock.BasicReader.readBlockData and all its implementers, which is ugly
as readBlockData should not care about caching.
> Avoiding caching during scans is somewhat important for us.

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