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From Clinton Begin <clinton.be...@gmail.com>
Subject Re: Migrating from ibatis 2 to 3
Date Fri, 05 Mar 2010 02:54:26 GMT
As I said, it's fine to share sqlmapclient... But not sessions.

And you wouldn't have to modify iB3 to implement a a multi-thread
capable sqlmapclient-like class.

Clinton

On 2010-03-04, François Schiettecatte <fschiettecatte@gmail.com> wrote:
> Clinton
>
> Thanks for explaining that, much clearer now and it makes my code simpler. I
> know I *could* modify the iBATIS 3 code but I am loath to do that because it
> would introduce variability.
>
> FWIW iBATIS 2 was completely stable sharing SqlMapClient, I had no issues
> for 18 months.
>
> Cheers
>
> François
>
>
> On Mar 4, 2010, at 9:22 AM, Clinton Begin wrote:
>
>>>> Session Level Cache ... does not work if the data has been changed by
>>>> another process
>>
>> The session level cache is exactly that... session level.  It only
>> clears things local to your session.  If another process changes data,
>> you should have cache flushing rules in place to cause the cache to
>> flush upon writing.  This is no different than iBATIS 2.0.
>>
>>>> sharing sql sessions across threads
>>
>> Neither iBATIS 2 or 3 are safe to share sessions between threads.  If
>> it's working for you in iBATIS 2, you're getting lucky, and it will
>> fail some day.
>>
>> iBATIS 2 had the SqlMapClient, which was "thread safe" because it used
>> a ThreadLocal variable to manage the sessions for you.  But the
>> sessions themselves are not thread safe.
>>
>> iBATIS 3 has done away with the ThreadLocal API, in favor of better
>> practices like Dependency Injection.   But it would take all of 30
>> seconds for you to create your own ThreadLocal manager (you could
>> practically copy the iBATIS 2.0 SqlMapClient).
>>
>> But definitely review your code to ensure you're not sharing sessions
>> across threads... Session == Connection... so that's that's very bad.
>>
>>
>> Cheers,
>> Clinton
>>
>> 2010/3/4 François Schiettecatte <fschiettecatte@gmail.com>:
>>> Hi
>>>
>>> I have been migrating a project from ibatis 2 to 3 and have run into some
>>> issues, mostly to do with connection pool management (C3P0), and I will
>>> write up my notes on my blog once I am done.
>>>
>>> Two issues specifically with the Session Level Cache:
>>>
>>> ---------
>>> Clearing the Session Level Cache
>>>
>>>        void clearCache()
>>>
>>> The SqlSession instance has a local cache that is cleared upon update,
>>> commit, rollback and close. To close it explicitly (perhaps with the
>>> intention to do more work), you can call clearCache().
>>> ---------
>>>
>>> One issue is that it seems to cache selects which does not work if the
>>> data has been changed by another process, running the select again in the
>>> same session returns stale data.
>>>
>>> The other problem has to do with sharing sql sessions across threads
>>> (which worked fine in 2). Running multiple selects through the same
>>> session gives me casting errors generated by line 88 in BaseExecutor:
>>>
>>>       localCache.putObject(key, EXECUTION_PLACEHOLDER);
>>>
>>> What seems to be happening is that the same query is coming in on one
>>> thread and generates a hit on the localCache before the search is done on
>>> another thread.
>>>
>>> Note that I am using C3P0 here which recommends caching sessions as much
>>> as possible and it could be that I am not using the stack correctly, but
>>> what I was doing worked fine in 2.x under heavy load.
>>>
>>> Cheers
>>>
>>> François
>>>
>>>
>>> --
>>> François Schiettecatte
>>> 35 Washington Square North, #2
>>> Salem, MA, 01970
>>> 617-909-2504
>>> http://fschiettecatte.wordpress.com/
>>>
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>>>
>>
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>
>
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