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From Michael Bouschen <mbo.t...@spree.de>
Subject Re: query timeout in JDO
Date Thu, 10 Dec 2009 07:54:26 GMT
Hi Craig,

I like the proposal. It solves the issue of having different timeout 
values for read and write operation and the wording makes clear that the 
scope of the timeout value is the datastore operation.

About the exception thrown in case of a timeout. I agree with what is 
written in the minutes of the JDO TCK conference call: it is ok to throw 
a JDODatastoreException, no need for a specific exception.

Regards Michael

> Hi Michael,
>
> Good summary.
>
> The original request for this feature was to allow queries that were 
> either stuck (possible deadlock) or running away (query too complex 
> for the server to complete timely).
>
> Then, Jörg added a request for updates to time out if they were stuck.
>
> And others wanted to know whether the timeout applied to memory 
> operations or just database operations.
>
> I'd like to propose something completely different that attempts to 
> resolve all of the above issues.
>
> Define two new properties and associated apis: 
> DatastoreReadTimeoutMillis and DatastoreWriteTimeoutMillis. Get rid of 
> the QueryTimeoutMillis property.
>
> DatastoreReadTimeoutMillis applies to all operations on the datastore 
> that are associated with reading data, including getObjectById, 
> queries, refresh, navigation, and lazy loading of fields or properties.
>
> DatastoreWriteTimeoutMillis applies to all operations on the datastore 
> that are associated with writing data, including flush, commit, delete 
> by query.
>
> If multiple datastore operations are involved in satisfying a user 
> request, the timeout applies individually to each of them.
>
> The rules for specifying the timeout are the same as in the original 
> proposal: if specified on a query, the timeout applies only to that 
> query, with the default coming from the PM. If the operation is 
> related to a PM operation, the timeout comes from the PM api, with the 
> default coming from the PMF.
>
> Whether there is a timeout is determined by the optional features 
> property. I don't know of a datastore that supports read and write 
> timeouts separately, so the feature can simply be called 
> DatastoreTimeout and it either is supported or not.
>
> Craig
>
> On Nov 17, 2009, at 12:05 AM, Michael Bouschen wrote:
>
>> Hi,
>>
>> the current spec allows specifying a query timeout on a Query, a PM 
>> or a PMF. The PM defines the default for all Query instances of the 
>> PM and the PMF defines the default value for all PMs of that PMF. 
>> However, there are still three open issue in the query timeout area:
>>
>> (1) query timeout as an optional feature
>> I propose to add query timeout as an optional feature. This means the 
>> collection returned by the PMF method supportedOptions includes the 
>> string "javax.jdo.option.QueryTimeout", if the JDO implementation and 
>> the datastore bound to the PMF supports query timeout. This would be 
>> a change in chapter 11.6 "Optional Feature Support" of the spec.
>>
>> (2) Scope of the query timeout value
>> I propose that a query timeout value set for a PM applies to all 
>> "datastore query" operations issued by the PM. This includes 
>> relationship navigation, findByObjectId and lasy loading of collections.
>> But how about modifying operations such as update, delete and insert? 
>> Does it make sense to apply the PM's query timeout for these 
>> operationsas well? I think this makes sense, but it might be less 
>> obvious, because these operations are part of the transaction commit. 
>> See also Jörg's recent email with subject "update timeout". This 
>> would be a change in chapter 12 PersistenceManager. Today chapter 
>> 12.6.3 "Query factory interface" specifies method setQueryTimeout. If 
>> we broaden the scope of a query timeout set on a PM, it might make 
>> sense to specify this in its own section, e.g. 12.6.9 "Query Timeout".
>>
>> (3) Definition of query timeout: datastore operation or JDO method?
>> Does the query timeout apply to the underlying datastore operation or 
>> does it define the maximum execution time of the JDO method such as 
>> Query.execute?
>> I propose the former, meaning use the query timeout value for the 
>> datastore operation. Otherwise, the JDO implementation would need to 
>> calculate the timeout for the datastore operation and need o guess 
>> the time needed to post-process the query result. If the datastore 
>> has the JDBC standard second resolution, and there is less than 1000 
>> millis left in the timeout, what should be the timeout set on the 
>> datastore query statement?
>>
>> What do you think?
>>
>> Regards Michael
>> -- 
>> *Michael Bouschen*
>> *Prokurist*
>>
>> akquinet tech@spree GmbH
>> Bülowstr. 66, D-10783 Berlin
>>
>> Fon:   +49 30 235 520-33
>> Fax:   +49 30 217 520-12
>> Email: michael.bouschen@akquinet.de
>> Url:    www.akquinet.de <http://www.akquinet.de>
>>
>> akquinet tech@spree GmbH, Berlin
>> Geschäftsführung: Martin Weber, Prof. Dr. Christian Roth
>> Amtsgericht Berlin-Charlottenburg HRB 86780 B
>> USt.-Id. Nr.: DE 225 964 680
>>
>> -- 
>> *Michael Bouschen*
>> *Prokurist*
>>
>> akquinet tech@spree GmbH
>> Bülowstr. 66, D-10783 Berlin
>>
>> Fon:   +49 30 235 520-33
>> Fax:   +49 30 217 520-12
>> Email: michael.bouschen@akquinet.de
>> Url:    www.akquinet.de <http://www.akquinet.de>
>>
>> akquinet tech@spree GmbH, Berlin
>> Geschäftsführung: Martin Weber, Prof. Dr. Christian Roth
>> Amtsgericht Berlin-Charlottenburg HRB 86780 B
>> USt.-Id. Nr.: DE 225 964 680
>>
>> -- 
>> *Michael Bouschen*
>> *Prokurist*
>>
>> akquinet tech@spree GmbH
>> Bülowstr. 66, D-10783 Berlin
>>
>> Fon:   +49 30 235 520-33
>> Fax:   +49 30 217 520-12
>> Email: michael.bouschen@akquinet.de
>> Url:    www.akquinet.de <http://www.akquinet.de>
>>
>> akquinet tech@spree GmbH, Berlin
>> Geschäftsführung: Martin Weber, Prof. Dr. Christian Roth
>> Amtsgericht Berlin-Charlottenburg HRB 86780 B
>> USt.-Id. Nr.: DE 225 964 680
>
> Craig L Russell
> Architect, Sun Java Enterprise System http://db.apache.org/jdo
> 408 276-5638 mailto:Craig.Russell@sun.com
> P.S. A good JDO? O, Gasp!
>


-- 
*Michael Bouschen*
*Prokurist*

akquinet tech@spree GmbH
Bülowstr. 66, D-10783 Berlin

Fon:   +49 30 235 520-33
Fax:   +49 30 217 520-12
Email: michael.bouschen@akquinet.de
Url:    www.akquinet.de <http://www.akquinet.de>

akquinet tech@spree GmbH, Berlin
Geschäftsführung: Martin Weber, Prof. Dr. Christian Roth
Amtsgericht Berlin-Charlottenburg HRB 86780 B
USt.-Id. Nr.: DE 225 964 680

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