TrackerDistributedCacheManager takes a blocking lock fo a loop that executes
10K times
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Key: MAPREDUCE-1909
URL: https://issues.apache.org/jira/browse/MAPREDUCE-1909
Project: Hadoop Map/Reduce
Issue Type: Improvement
Reporter: Dick King
Assignee: Dick King
In {{TrackerDistributedCachaManager.java}} , the portion where the cache is
cleaned up, the lock is taken on the main hash table and then all the entries
are scanned to see if they can be deleted. That's a long lockage. The table
is likely to have 10K entries.
I would like to reduce the longest lock duration by maintaining the set of
{{CacheStatus}} es to delete incrementally.
1: Let there be a new {{HashSet}}, {{deleteSet}}, that's protected under
{{synchronized(cachedArchives)}}
2: When {{refcount}} is decreased to 0, move the {{CacheStatus}} from
{{cachedArchives}} to {{deleteSet}}
3: When seeking an existing {{CacheStatus}}, look in {{deleteSet}} if it isn't
in {{cachedArchives}}
4: When {{refcount}} is increased from 0 to 1 in a pre-existing {{CacheStatus}}
[see 3:, above] move the {{CacheStatus}} from {{deleteSet}} to
{{cachedArchives}}
5: When we clean the cache, under {{synchronized(cachedArchives)}} , move
{{deleteSet}} to a local variable and create a new empty {{HashSet}}. This is
constant time.
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