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Re: Opening multiple database channels
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Re: Opening multiple database channels

  • Subject: Re: Opening multiple database channels
  • From: John Huss <email@hidden>
  • Date: Fri, 23 Mar 2012 12:56:31 -0500
Cayenne supports this kind of concurrency and will utilize multiple connections to the database without requiring a duplicate stack like EOF does.  So for concurrency it is a much better choice than EOF.   And it's easy to get started if you're familiar with EOF already.  It can be used inside a WO app with no problems.

John

On Fri, Mar 23, 2012 at 10:58 AM, Ramsey Gurley <email@hidden> wrote:
My main goal is to better understand EOF conceptually :-) I was playing with the ERXOSCPool just for kicks and found a leak. I wondered why an entirely new OSC was even needed to make a second connection to the db.  Seems like overkill. So I fugetuboutit.

Later, I'm rereading through the old docs and find that little gem about opening new database channels.  It seems that at least conceptually, creating new channels would be the proper way to handle multiple connections to the database.

But it doesn't work. After finding the object store lock… I wonder if it ever worked?  The fact that it was documented makes me think that maybe once upon a time, it worked.  However, this wouldn't be the first time the docs were totally wrong.  The fact that it suggests making every session in the app a listener for that notification only reinforces my suspicions that the docs were just wrong.

Because of the lock, that notification is only ever fired once. So it's possible to create multiple connections, but only one of them will ever be used. The docs also suggest that an EODatabase may have multiple EODatabaseContexts.  But then this will have the same problem with the object store lock and may even exhibit the same problem that results in leaks in the OSCPool.

I'm coming to the conclusion that the best way to distribute load across multiple channels would be to simply have multiple instances of an app. Knowing that would definitely have an influence on any sort of bulk processing operations I might design in the future.

I also wonder if this information can be used to implement more effective load balancing.  No reason to direct users to an instance if one user on that instance has EOF tied up fetching a large blob out of the database for instance. I'll have to look for the location of the load balancer in WO sometime.  I'd like to see how it works.

Anyway, thanks for all the input everyone :-) I think I understand the point of the object store lock now.

Ramsey

On Mar 22, 2012, at 7:53 PM, Chuck Hill wrote:

> OK, so... my first question has to be "what is your goal?  What are you trying to accomplish?"  This is NOT going to make EOF multi-threaded.
>
>
> Chuck
>
>
> On 2012-03-22, at 7:34 PM, Ramsey Gurley wrote:
>
>> Hi all,
>>
>> I'm looking at trying to open multiple database channels in a single instance of a WO app. No reason, just wondering if it can be done.  I know there's ERXObjectStoreCoordinator pool, but this conceptually seems like the wrong way to do it.  Maybe I want 4 open connections for one database, but only one on another… whatever.  So I have a look at
>>
>> https://developer.apple.com/legacy/mac/library/documentation/WebObjects/Enterprise_Objects/Connecting/Connecting.html#//apple_ref/doc/uid/TP30001011-CH210-TPXREF145
>>
>> and this seems to be the answer to my question.  Well, until I try it. It turns out that inside of objectsWithFetchSpec on EOEditingContext, the objectstore is locked before a fetch takes place. As a result, no other fetch can proceed until the object store is unlocked.  The answer seemed suspicious in the fact that it's being done on the Session anyway...
>>
>> So, I guess my question boils down to… is it even possible? Is this the 'single EOF lock' that Chuck Hill and Ravi Mendis were referring to in a previous list message?
>>
>> Thanks,
>>
>> Ramsey
>>
>>
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> --
> Chuck Hill             Senior Consultant / VP Development
>
> Practical WebObjects - for developers who want to increase their overall knowledge of WebObjects or who are trying to solve specific problems.
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  • Follow-Ups:
    • Re: Opening multiple database channels
      • From: Mai Nguyen <email@hidden>
References: 
 >Opening multiple database channels (From: Ramsey Gurley <email@hidden>)
 >Re: Opening multiple database channels (From: Ramsey Gurley <email@hidden>)

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