[jira] [Updated] (HBASE-5898) Consider double-checked locking for block cache lock

["Todd Lipcon (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HBASE-5898?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Todd Lipcon updated HBASE-5898:
-------------------------------

    Attachment: hbase-5898.txt

Here's a patch which implements the double checked locking. The first attempt to look up the value does so without locking it. If it fails, then it tries to acquire the lock, and checks again. If the re-check fails, then it actually goes to disk. Assuming that going to disk is slow, the extra check of cache should be inconsequential, but this made a big difference in throughput of a read-only in-cache workload.
                
> Consider double-checked locking for block cache lock
> ----------------------------------------------------
>
>                 Key: HBASE-5898
>                 URL: https://issues.apache.org/jira/browse/HBASE-5898
>             Project: HBase
>          Issue Type: Improvement
>          Components: performance
>    Affects Versions: 0.94.1
>            Reporter: Todd Lipcon
>         Attachments: hbase-5898.txt
>
>
> Running a workload with a high query rate against a dataset that fits in cache, I saw a lot of CPU being used in IdLock.getLockEntry, being called by HFileReaderV2.readBlock. Even though it was all cache hits, it was wasting a lot of CPU doing lock management here. I wrote a quick patch to switch to a double-checked locking and it improved throughput substantially for this workload.

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