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From "Clinton Begin" <clinton.be...@gmail.com>
Subject Re: iBATIS lock timeouts
Date Mon, 21 Jul 2008 14:53:03 GMT
Haha... see, even I screw it up!  I reversed up sessions and transactions.
My example here, while it would work, would be kind of silly.

The most important thing is the Note section in the book.  I forgot we put
that warning of future deprecation in there.  :-)

If we find that iBATIS does need throttling in the future, we'd likely put
it at the top level and only have one setting.


On Mon, Jul 21, 2008 at 8:31 AM, Hugh Ross <hh4ross@gmail.com> wrote:

> Thanks.  Very helpful.  Agree that these things are more properly the
> responsibility of "containers."
> Just reread the section of the SQL Maps Developer Guide that covers these
> settings.  Your maxTransactions example below seems to differ from the
> documented usage.
> With earlier versions of iBATIS, can we set them to 0 (or something) to
> suppress their action?
> On 7/20/08, Clinton Begin <clinton.begin@gmail.com> wrote:
>> Unfortunately it was a pretty deep implementation detail.  Essentially
>> there used to be 3 settings:
>> maxSessions
>> maxTransactions
>> maxRequests
>> A session was a user thread accessing nearly any part of the framework.  A
>> transaction was a database connection and transaction.  A request was an
>> executing SQL statement.  So essentially you could configure something
>> like:  5 sessions, 15 transactions (avg. two per session), and 60 requests
>> (avg. four per transaction).  Note that these are limits on how many of
>> these could be active at any one time, not how many can be created etc.
>> A Throttle was the implementation of the limitation.  In a nutshell, it
>> was the Guarded Suspension pattern that blocked with a wait until a session,
>> transaction or request became available.
>> This is similar to the throttling that EJBs and Spring (?) would normally
>> do.  Typical usages were to avoid hitting the database too hard, avoid
>> running out of open cursors in oracle, or to avoid opening too many
>> connections at once.
>> The problems were:
>>   * The settings were confusing, most people didn't understand them (not
>> their fault) and therefore they were often set incorrectly.
>>   * The behavior was duplicated, as the app server of container framework
>> (Spring), and even the datasource  were likely throttling or limiting such
>> activity already.
>>   * The throttle features hid the underlying problems which were usually
>> caused by not properly ending transactions or closing connections.
>> (try/finally)
>>   * Some complained about the blocking and synchronization required to
>> implement this feature.
>> So the behavior was superfluous and the errors were vague.  All for
>> something that wasn't really the responsibility of iBATIS to handle.  So it
>> was removed.
>> The caveat is that you will now know if your application has a problem.
>>   * If you fail to end transactions (i.e. close connections) your
>> datasource or database will complain.
>>   * If you hit your database too hard, you'll see performance degrade as
>> threads contend for resources.
>>   * If you try to run too many statements, your database may complain
>> about too many open cursors.
>> The advantage is that:
>>   * The throttling is no longer duplicated in various layers of your
>> application.
>>   * Performance should be generally better once you tune some other
>> throttle or fix mismanaged connections.
>>   * You'll get the proper error that will tell you what the real problem
>> is.
>> If you want to throttle iBATIS yourself, you can do so fairly simply with
>> a dynamic proxy between the SqlMapClient interface and the SqlMapClientImpl
>> -- perhaps I should release something of the sort as a plug-in?
>> But I highly recommend you hunt down the actual problem with your
>> application.. If you're getting deadlocks, that could either be unclosed
>> connections, poorly written stored procedures or resources that are
>> allocated out of order.  The problems were always there, iBATIS was just
>> hiding them "for you".... hope that helps.
>> Cheers,
>> Clinton
>> On Sun, Jul 20, 2008 at 8:01 AM, Hugh Ross <hh4ross@gmail.com> wrote:
>>> Clinton,
>>> Can you send us a link to more detail on this thread throttling, perhaps
>>> in wiki or release notes?
>>> Thanks...
>>>   On 7/17/08, Clinton Begin <clinton.begin@gmail.com> wrote:
>>>> I've removed all thread throttling from iBATIS.  It was causing a great
>>>> deal of confusing and people complained about performance.   The thread
>>>> throttling was quite advanced and had a lot of scalability testing behind
>>>> it, it was able to hide a lot of problems like this.
>>>> The downside is that you now have to make sure you're not throwing too
>>>> much at your database.  The way you've solved it is probably the way it
>>>> should have been originally.  iBATIS was hiding the problem for you, which
>>>> was sometimes a feature, and other times a bug.  At least now you know
>>>> what's really going on... :-)
>>>> That said, it's also possible that you're not closing your transactions
>>>> properly.  The thread throttling in past releases also did a good job of
>>>> hiding that from you as well.. but now you'll start to see the database
>>>> complain about such errors. Again, sometimes a feature, other times a bug.
>>>> Clinton
>>>> On Thu, Jul 17, 2008 at 9:55 AM, Michael Schall <mike.schall@gmail.com>
>>>> wrote:
>>>>> Production Environment:
>>>>> We are using a JNDI datasource in WS 6.1 (fixpack 15) to connect to a
>>>>> DB2 9.1 (fixpack 2) database on a separate cluster.
>>>>> We recently upgraded our Java version of iBATIS after falling way
>>>>> behind from 2.0.9 to the latest release 2.3.1.
>>>>> The dev and test environment showed no issues with the upgrade.
>>>>> When rolling out to production we started getting lock timeouts that
>>>>> would bring the system down under heavy load.
>>>>> We did not recreate the JNDI datasource or replace any database drivers
>>>>> on the WebSphere machines or make any configuration changes within DB2
>>>>> (other than new tables/columns) during the latest release.
>>>>> We first thought the default IsolationLevel had changed from "Cursor
>>>>> Stability" to "Read Stability", but that is actually the default
>>>>> IsolationLevel when connecting from WS to DB2 using JNDI.  However, as
>>>>> troubleshooting step, we set the IsolationLevel within the JNDI datasource
>>>>> to 2 (Cursor Stability), which is allowing our system to avoid the lock
>>>>> timeouts.
>>>>> I have looked throught the change log and nothing seems to point to the
>>>>> issue we are having.   Any ideas on where our problem might be?
>>>>> Thanks for your time.
>>>>> Mike

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