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https://issues.apache.org/jira/browse/MAPREDUCE-6197?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15333020#comment-15333020
]
Jian He commented on MAPREDUCE-6197:
------------------------------------
lgtm,
one question is how/why do you choose such policy for determining the weight ?
{code}
maximumWeight(MAX_WEIGHT).weigher(
new Weigher<AttemptPathIdentifier, AttemptPathInfo>() {
@Override
public int weigh(AttemptPathIdentifier key,
AttemptPathInfo value) {
return key.jobId.length() + key.user.length() +
key.attemptId.length()+
value.indexPath.toString().length() +
value.dataPath.toString().length();
}
}
)
{code}
> 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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