[infinispan-dev] Passivation and BCHM WAS: fixing eviction with transactions (critical for Hibernate Search)

[Galder Zamarreño]

On Jun 10, 2011, at 3:18 PM, Sanne Grinovero wrote:

> </snip>
> 
> 3) so every time we evict an entry, we write it to the store.. I guess
> that leads to re-write quite often values which are already in the
> store, and for which there's no need to store again. I think this
> argument came up before, but we didn't want to track an additional
> boolean to keep the memory need low. Still when we're using it as a
> cache with eviction rules in place, it seems to me that overall
> performance would be better by avoiding more writes at the cost of
> being able to store some less entries in memory.

Hmmm, are you still talking about passivation? If you do, passivation does not work like that. With passivation, when an entry is stored, it's removed from memory, and when it's activated, it's removed from the store and put in memory. 

So, your theory of re-writing the entry is not right for passivation. If you have a simple cache loader set up with eviction, then your issue does not happen either unless there's a modification of the entry in memory.

I'm not sure what boolean you're talking about...

> 
> Cheers.
> Sanne
> 
> 2011/6/10 Manik Surtani <manik at jboss.org>:
>> So I've taken on this sub-task from Sanne (ISPN-1169), and here is the deal:
>> BCHM analyses whether or not to evict stuff every time an operation (put,
>> get, replace) is run, based on the configured eviction policy (LIRS, LRU or
>> NONE).  It does so by calling evictionStrategy.execute(), which returns a
>> Set of hash entries removed from the BCHM.
>> https://github.com/infinispan/infinispan/blob/master/core/src/main/java/org/infinispan/util/concurrent/BoundedConcurrentHashMap.java#L341
>> Note that execute() actually removes entries from the BCHM, so after
>> execute() is called, these entries are no longer in the BCHM!
>> This is set is then sent to the EvictionManager
>> https://github.com/infinispan/infinispan/blob/master/core/src/main/java/org/infinispan/eviction/EvictionManager.java#L61
>> which in turn passivates the evicted entries:
>> https://github.com/infinispan/infinispan/blob/master/core/src/main/java/org/infinispan/eviction/EvictionManagerImpl.java#L189
>> So we have a window where the entry is neither accessible from memory or
>> from a cache store, since it is "in-fly".
>> My proposed fix is to:
>> 1) Make sure the PassivationManager is passed in to the DataContainer, and
>> available to any EvictionStrategy
>> 2) EvictionStrategies ensure passivation occurs *before* removing an entry
>> from the BCHM
>> 3) The additional window of a reader thread in the ActivationInterceptor
>> determining that an entry is in memory and bypasses activation, only to find
>> that the entry has been removed from the BCHM by the time it gets to it,
>> should not be a problem since when testing the DataContainer in the
>> ActivationInterceptor, the entry is placed in the caller's InvocationContext
>> so a handle on the entry is there.
>> Does anyone have any concerns with this?  Vladimir, does this adversely
>> affect the BCHM/EvictionStrategy design?
>> Cheers
>> Manik
>> On 8 Jun 2011, at 19:15, Vladimir Blagojevic wrote:
>> 
>> On 11-06-08 12:10 PM, Sanne Grinovero wrote:
>> 
>> Yes, we're on the same channel now. That's exactly what I meant
>> 
>> yesterday on IRC when mentioning the BoundedCHM, and what I meant
>> 
>> above with "we should acquire it before it's actually evicted".
>> 
>> But this issue is getting complex, I've split it in 4 different
>> 
>> problems and I'm going to solve the first three soon, the BoundedCHM
>> 
>> is the fourth and I'm not sure I'll fix that today.
>> 
>> Sanne,
>> 
>> Sounds good, please consult us when it comes to changing BCHM!
>> 
>> Cheers.
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>> 
>> --
>> Manik Surtani
>> manik at jboss.org
>> twitter.com/maniksurtani
>> Lead, Infinispan
>> http://www.infinispan.org
>> 
>> 
>> 
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> 
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--
Galder Zamarreño
Sr. Software Engineer
Infinispan, JBoss Cache