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https://issues.apache.org/jira/browse/MAPREDUCE-1909?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12884485#action_12884485
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Dick King commented on MAPREDUCE-1909:
--------------------------------------
Might as well make our unique directory names with
{noformat}
static private AtomicLong uniqueDirNumber = new AtomicLong();
...
String uniqueString = "D" + uniqueDirNumber.getAndIncrement();
{noformat}
if we're in the area.
> TrackerDistributedCacheManager takes a blocking lock fo a loop that executes
> 10K times
> --------------------------------------------------------------------------------------
>
> 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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