[jira] [Commented] (MAPREDUCE-6197) Cache MapOutputLocations in ShuffleHandler

["Junping Du (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MAPREDUCE-6197?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15328449#comment-15328449 ] 

Junping Du commented on MAPREDUCE-6197:
---------------------------------------

The similar issue get fixed for Hive in HIVE-9912. Attache a patch refer most of the original patch but remove the dirWatcher.

> Cache MapOutputLocations in ShuffleHandler
> ------------------------------------------
>
>                 Key: MAPREDUCE-6197
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-6197
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>    Affects Versions: 2.6.0
>            Reporter: Siddharth Seth
>            Assignee: Junping Du
>         Attachments: MAPREDUCE-6197.patch
>
>
> ShuffleHandler currently seems to create a map of mapId - mapInfo (file.out / index information) when it receives a message.
> This should be caching map info across requests, so that the a scan of all directories is not required for each reducer fetching from the same map.
> Also, the scan for each map output / index file is performed twice per mapId within a request. In populateHeaders - once in the call to getMapOutputInfo, and then directly in the method.
> For an invocation where we do end up with more than 1000 (default) mapIds in a single call, and don't cache them in the map - the path constructed for such entries will be invalid. This is highly unlikely to be the case though, until there's proper caching.
> {code}
> MapOutputInfo info = mapOutputInfoMap.get(mapId);
>           if (info == null) {
>             info = getMapOutputInfo(outputBasePathStr, mapId, reduceId, user);
>           }
> {code}



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