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From Murtuza Boxwala <mboxw...@pivotal.io>
Subject GEODE-6637
Date Thu, 27 Jun 2019 14:11:55 GMT
Problem:

Every time we make a put the code in BucketRegion.searchAndLock and BucketRegion.removeAndNotifyKeys
locks (synchronized) on a hash map, the allKeysMap, to checkout the key to be modified and
prevent anyone else from updating at the same time. This area of the code gets a lot of contention,
especially if the same keys are getting checked out.

Deeper Problem:

In trying to fix this, I would like to use a different data structure, like a ConcurrentHashMap
but am running across a problem.  It seems that when we want to put a single item, we end
up calling the same code that putAll calls, and we just wrap the single key in an array. It
further seems that the entire allKeysMap is synchronized because we want to lock multiple
keys at the same time and do the putAll ‘atomically.’

Question

Is there any reason that putAll needs to lock all the keys and insert at the same-ish time.
Could putAll be turned into something that looked like: 

public void putAll(entries)
	for(Entry entry: entries)
		put(entry.key, entry.value)

Or is it important that they all happen together?  Does putAll guarantee some kind of transactional
properties?

An analogy

Imagine a restaurant (our hash map) that has a bunch of tables built for 1 person (think classroom
chairs with a pull out desk).  PutAll is like coming to this restaurant and asking for a table
for four people.  Now someone has to go, find four tables, pull them together, etc…you know
how it goes.


Any help is appreciated.

Thanks,
Murtuza

https://issues.apache.org/jira/browse/GEODE-6637
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