[MAPREDUCE-6197] Cache MapOutputLocations in ShuffleHandler

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.6.0
• Fix Version/s: 2.9.0, 3.0.0-alpha1
• Target Version/s: 2.9.0
• Hadoop Flags: Reviewed
• Assignee: Junping Du
• Reporter: Siddharth Seth
• Created: 16/Dec/14 01:07
• Updated: 29/Aug/19 09:25
• Resolved: 21/Jun/16 21:26

Description

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.

MapOutputInfo info = mapOutputInfoMap.get(mapId);
          if (info == null) {
            info = getMapOutputInfo(outputBasePathStr, mapId, reduceId, user);
          }

Issue Links

• relates to: MAPREDUCE-7237 Supports config the shuffle's path cache related parameters