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From "Josh Elser (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-3982) Add LRU mechanism to address memory concerns and possibly pre-fetch Tablet Locations.
Date Mon, 31 Aug 2015 17:56:47 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-3982?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14723778#comment-14723778
] 

Josh Elser commented on ACCUMULO-3982:
--------------------------------------

bq. he Locator needs more testing: for example, it always uses a single write lock to serialize
lookups, which is a bad behavior for random tablet lookups. Locator does some simple read-ahead.
Is it enough? Is it too much?

We've had a number of requests to get a Locator impl into the public API. Perhaps now would
be a good time to refactor it into the API and make sure we can adequately test it? Would
be happy to try to help get behind this.

> Add LRU mechanism to address memory concerns and possibly pre-fetch Tablet Locations.
> -------------------------------------------------------------------------------------
>
>                 Key: ACCUMULO-3982
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-3982
>             Project: Accumulo
>          Issue Type: New Feature
>          Components: client, tserver
>    Affects Versions: 1.6.3, 1.7.0, 1.8.0
>            Reporter: marco polo
>            Assignee: Eric Newton
>             Fix For: 1.8.0
>
>
> On larger systems, especially those of which may split frequently, I've seen churn in
the TabletLocator caches. Could we possibly pre-fetch entries for a table so that we don't
constantly access the metadata table for tablet locations. 
> Additionally, instead of clearing the cache in the case of a miss or failure, could we
simply update those entries in the cache? If we do this we may minimize cache misses overall
and the need to scan the meta data table. If need be, we could have a threshold before clearing
the cache entirely if people see the need for that.
> It would also be helpful to add an LRU cache ( or maybe even priority based LRU cache
). In ACCUMULO-3549, we added a cache clear to TabletServer to avoid overwhelming memory.
An LRU cache might address this concern and make the clear cache call unnecessary.



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