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Date: Wed, 24 Jun 2009 15:34:07 -0700 (PDT)
From: "Jonathan Gray (JIRA)" <jira@apache.org>
To: hbase-dev@hadoop.apache.org
Subject: [jira] Commented: (HBASE-1460) Concurrent LRU Block Cache
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    [ https://issues.apache.org/jira/browse/HBASE-1460?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12723778#action_12723778 ] 

Jonathan Gray commented on HBASE-1460:
--------------------------------------

Came across this interesting project:  http://code.google.com/p/concurrentlinkedhashmap/

Their "old algorithm" is much like this one.  The new algoirthm looks very cool but is not production ready yet.

> Concurrent LRU Block Cache
> --------------------------
>
>                 Key: HBASE-1460
>                 URL: https://issues.apache.org/jira/browse/HBASE-1460
>             Project: Hadoop HBase
>          Issue Type: Improvement
>          Components: io
>            Reporter: Jonathan Gray
>            Assignee: Jonathan Gray
>             Fix For: 0.20.0
>
>         Attachments: HBASE-1460-v1.patch, HBASE-1460-v2.patch, HBASE-1460-v3.patch
>
>
> The LRU-based block cache that will be committed in HBASE-1192 is thread-safe but contains a big lock on the hash map.  Under high load, the block cache will be hit very heavily from a number of threads, so it needs to be built to handle massive concurrency.
> This issue aims to implement a new block cache with LRU eviction, but backed by a ConcurrentHashMap and a separate eviction thread.  Influence will be drawn from Solr's ConcurrentLRUCache, however there are major differences because solr treats all cached elements as equal size whereas we are dependent on our HeapSize interface with realistic (though approximate) heap usage.

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