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From "Yu Li (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-14463) Severe performance downgrade when parallel reading a single key from BucketCache
Date Sun, 08 Nov 2015 13:27:11 GMT

    [ https://issues.apache.org/jira/browse/HBASE-14463?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14995627#comment-14995627
] 

Yu Li commented on HBASE-14463:
-------------------------------

Thanks [~tedyu] for help commit, and thanks all for review!

Regarding patch for 0.98, I could prepare a patch with only WeakObjectPool but no changes
in KeyLocker, or a full backport of HBASE-14268. [~apurtell] please let me know which way
you prefer. Thanks.

> Severe performance downgrade when parallel reading a single key from BucketCache
> --------------------------------------------------------------------------------
>
>                 Key: HBASE-14463
>                 URL: https://issues.apache.org/jira/browse/HBASE-14463
>             Project: HBase
>          Issue Type: Bug
>    Affects Versions: 0.98.14, 1.1.2
>            Reporter: Yu Li
>            Assignee: Yu Li
>             Fix For: 2.0.0, 1.2.0, 1.3.0, 0.98.17
>
>         Attachments: 14463-branch-1-v12.txt, GC_with_WeakObjectPool.png, HBASE-14463.patch,
HBASE-14463_v11.patch, HBASE-14463_v12.patch, HBASE-14463_v12.patch, HBASE-14463_v2.patch,
HBASE-14463_v3.patch, HBASE-14463_v4.patch, HBASE-14463_v5.patch, TestBucketCache-new_with_IdLock.png,
TestBucketCache-new_with_IdReadWriteLock.png, TestBucketCache_with_IdLock-latest.png, TestBucketCache_with_IdLock.png,
TestBucketCache_with_IdReadWriteLock-latest.png, TestBucketCache_with_IdReadWriteLock-resolveLockLeak.png,
TestBucketCache_with_IdReadWriteLock.png, pe_use_same_keys.patch, test-results.tar.gz
>
>
> We store feature data of online items in HBase, do machine learning on these features,
and supply the outputs to our online search engine. In such scenario we will launch hundreds
of yarn workers and each worker will read all features of one item(i.e. single rowkey in HBase),
so there'll be heavy parallel reading on a single rowkey.
> We were using LruCache but start to try BucketCache recently to resolve gc issue, and
just as titled we have observed severe performance downgrade. After some analytics we found
the root cause is the lock in BucketCache#getBlock, as shown below
> {code}
>       try {
>         lockEntry = offsetLock.getLockEntry(bucketEntry.offset());
>         // ...
>         if (bucketEntry.equals(backingMap.get(key))) {
>           // ...
>           int len = bucketEntry.getLength();
>           Cacheable cachedBlock = ioEngine.read(bucketEntry.offset(), len,
>               bucketEntry.deserializerReference(this.deserialiserMap));
> {code}
> Since ioEnging.read involves array copy, it's much more time-costed than the operation
in LruCache. And since we're using synchronized in IdLock#getLockEntry, parallel read dropping
on the same bucket would be executed in serial, which causes a really bad performance.
> To resolve the problem, we propose to use ReentranceReadWriteLock in BucketCache, and
introduce a new class called IdReadWriteLock to implement it.



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