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From Unico Hommes <un...@hippo.nl>
Subject Re: Turning off default MRU store
Date Fri, 05 Mar 2004 14:45:54 GMT
Geoff Howard wrote:

> Unico Hommes wrote:
>
>> Sylvain Wallez wrote:
>>
>>> Unico Hommes wrote:
>>>
>>>>
>>>> Unico Hommes wrote:
>>>>
>>>>>
>>>>>
>>>>> Corin Moss wrote:
>>>>>
>>>>>> Hi Guys,
>>>>>>
>>>>>> I might be getting ahead of myself a bit here, but I'm going to 
>>>>>> try and turn off the default MRU store, in favour of the JCS 
>>>>>> based persistent store.  I'd like to try some tests on 
>>>>>> performance without the default MRU - has anyone else tried 
>>>>>> anything similar? I've simply set the core store's role to point

>>>>>> to the JCS store implementation.
>>>>>>
>>>>>
>>>>> I guess I already got ahead of you when I renamed 
>>>>> JCSPersistentStore JCSStore just now :-) (And merged it with the 
>>>>> AbstractJCSStore BTW). It seems to me that JCS is both and it 
>>>>> could replace all three stores: DefaultStore, TransientStore and 
>>>>> PersistentStore.
>>>>>
>>>>
>>>> I have to add that this is not the whole story. We do actually need 
>>>> to distinguish between persistent and transient storage. Some 
>>>> components explicitly want to persist some data instead of just 
>>>> cache it for speed. But as far as caching is concerned I think it 
>>>> we can leave it completely up to JCS.
>>>
>>>
>>>
>>>
>>>
>>> Some components are explicitely using the transient-store to keep 
>>> data that shouldn't (or cannot) be serialized. But AFAIK, no 
>>> component directly uses the persistent-store except the store itself.
>>>
>>
>> To my knowlegde there is one in eventcache block that uses the 
>> PersistentStore to persist some info it needs to recover upon next 
>> startup.
>>
>> It does not look to me as though JCS would fit the PersistentStore 
>> role very well. I was thinking that perhaps. We could have JCSStore 
>> as a replacement for TransientStore and Store roles and use 
>> FilesystemStore for the PersistentStore role.
>
>
>
> Wait a minute.  The original issue that brought JCS to the front as 
> that the persistent store was broken and had license problems.  Are 
> you saying that JCS isn't a good candidate for persisting the cached 
> info to disk, or that the fact that it by default has an MRU memory 
> front-end makes it not map directly to persistent-store role cleanly?
>
IIUC, JCS will always use a memory store in front yes. And it suggests 
on the JCS website that the persistence process is not very reliable:

from http://jakarta.apache.org/turbine/jcs/IndexedDiskAuxCache.html :

"When the disk cache is properly shutdown, the memory index is written 
to disk and the value file is defragmented. When the cache starts up, 
the disk cache can be configured to read or delete the index file. This 
provides an unreliable persistence mechanism."

> The use of persistent store in eventcache shouldn't be a problem with 
> JCS as long as at shutdown, it persists everything it has in its MRU 
> if it hasn't already.  If there is some problem it would be much 
> better to just go back to the old serializing persistence for the 
> event cache data because the only benefit to putting it in the store 
> is that you more or less guaranteed that the events and cached 
> responses would be kept together.


Yes, giving up that feature would be too bad.

Unico




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