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

[Sanne Grinovero]

It looks as a good improvement, especially as we remove the locking,
but I still have some doubts:

1) as the passivation happens in the eviction thread, is that going to
be fast enough or hindering the eviction performance? especially with
LIRS, being this the user thread it means that put operations suffer a
mayor performance hit (for async caheloaders, see next point). Well
this was the case already, I guess.

2) with async stores, the issue is back. The value is not going to be
found while it's "in flight" in the async storage queue; so unless you
want to avoid supporting it for now, the actual removal from the
container should be performed from the async cache loader code.

So it looks like that - when passivation is enabled - the proper way
to implement this is to use the eviction policy only to identify
what's going to be removed from the container, but not to actually
remove it.

I'd still focus on having the best performance possible for the case
in which passivation is not enabled, that looks like the "performance
needing" setup, or maybe we need separate eviction strategies fro when
passivation is enabled.


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.

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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