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From Rafa Haro <rh...@apache.org>
Subject Re: Configuration Management at Transformation Connectors
Date Wed, 02 Jul 2014 08:17:17 GMT
Hi Karl,

First of all, thanks for your answers. I will read the proposed chapters 
but, please, find inline further questions:

El 01/07/14 19:21, Karl Wright escribió:
> Hi Rafa,
>
> Let me answer one question at a time.
>
> bq. I would like to initialize the configuration object only once per job
> execution. Because the configuration is not supposed to be changed during a
> job execution, I would like to be able to take the configuration parameters
> from ConfigParams and from Specification objects and create a unique
> instance of my configuration object.
>
> Connection instances are all pooled and reused.  You need to read about
> their lifetime.  ManifoldCF in Action chapter 6 (IIRC) is where you will
> find this: https://manifoldcfinaction.googlecode.com/svn/trunk/pdfs/
> You should also be aware that there is *no* prohibition on configuration or
> specification changing during a job run; the framework is structured,
> however, so that you don't need to worry about this when writing your
> connector.
I understand this Karl. And precisely because of the pooling, it is hard 
for me to believe that, during a job execution, the system is able to 
stop all the threads and to freeze the execution for initializing again 
all the connectors instances in the pool if the user changes the 
configuration. If this not actually happen, then for example in 
implementations like current Tika Extractor, the getPipelineDescription 
method will be returning always exactly the same output version for all 
the crawled documents in the current job. I understand the need to check 
the output version from job to job, but not per document in a single job.

Also, there is something I'm completely missing: what is the output 
specification and which is the difference with connectors and jobs 
configuration?
>
>
> bq. The getPipelineDescription method is quite confusing for me...
>
> Getting a version string and indexing a document may well be separated in
> time, and since it is possible for things to change in-between, the version
> string should be the basis of decisions your connector is making about how
> to do things.  The version string is what gets actually stored in the DB,
> so any differences will be picked up on later crawls.
>
> FWIW, the IRepositoryConnnector interface predates the decision to not
> include a document specification for every method call, and that has
> persisted for backwards compatibility reasons, although in MCF 2.0 that may
> change.  The current design enforces proper connector coding.
>
> bq. In the addOrReplaceDocumentWithExcept
> ion, why is the pipelineDescription passed by parameter instead of the
> connector Specification...?
>
> See answer above.
>
>
> bq. Is there a way to reuse a single configuration object per job
> execution? In the Output processor connector, I used to initialize my
> custom stuff in the connect method (I'm not sure if this strategy is valid
> anyway), but for the Transformation connectors I'm not even sure if this
> method is called.
>
> You really aren't supposed to have a *single* object, but rather one per
> connection instance.  Connection instances are long-lived, remember.  That
> object should also expire eventually if there is no use.  There's a
> particular design pattern you should try to adhere to, which is to have a
> getSession() method that sets up your long-lived member object, and have
> the poll() method free it after a certain amount of inactivity.  Pretty
> much all connectors these days use this pattern; for a modern
> implementation, have a look at the Jira connector.
Yes yes, of course. There would be a configuration object bounded to 
each connector instance, of course. The problem I'm facing is that I 
want to create this object only one time (could be perfectly a member of 
the connector) and I can't find a proper way/place to do it because I 
need both the configuration of the connector (ConfigParams, which is 
always available, so that is fine) and the Specification object (which 
seems to contain the job configuration data), which as far as I know is 
only passed in the getPipelineDescriptionMethod. I would like not to do 
the initialization in that method because it is called for each 
processed documents and I would like to avoid typical hack like 
"if(customConfig == null) customConfig = new CustomConfig(params, 
specification);"
>
>
> FWIW, there's no MCF in Action chapter on transformation connectors yet,
> but they are quite similar to output connectors in many respects, so
> reading Chapter 9 may help a bit.
>
> Thanks,
> Karl
Thanks to you Karl,

Cheers,
Rafa
>
>
>
>
> On Tue, Jul 1, 2014 at 1:04 PM, Rafa Haro <rharo@apache.org> wrote:
>
>> Hi guys,
>>
>> I'm trying to develop my first Transformation Connector. Before starting
>> to code, I have tried to read first enough documentation and I have also
>> studied the Tika extractor as transformation connector example. Currently,
>> I'm just trying to implement an initial version of my connector, starting
>> with something simple to later complicate the things a little bit. The
>> first problem I'm facing is the configuration management, where I'm
>> probably missing something. In my case, I need a fixed configuration while
>> creating an instance of the connector and a extended configuration per job.
>> Let's say that the connector configuration has to setup a service and the
>> job configuration will define how the service should work for each job.
>> With both configurations, I need to create an object which is expensive to
>> instantiate. Here is where the doubts raise:
>>
>> 1. I would like to initialize the configuration object only once per job
>> execution. Because the configuration is not supposed to be changed during a
>> job execution, I would like to be able to take the configuration parameters
>> from ConfigParams and from Specification objects and create a unique
>> instance of my configuration object.
>>
>> 2. The getPipelineDescription method is quite confusing for me. In the
>> Tika Extractor, this method is used to pack in a string the configuration
>> of the Tika processor. Then this string is again unpacked in the
>> addOrReplaceDocumentWithException method to read the documentation. My
>> question is why?. As far as I understand, the configuration can't change
>> during the job execution and according to the documentation "the contents
>> of the document cannot be considered by this method, and that a different
>> version string (defined in IRepositoryConnector) is used to describe the
>> version of the actual document". So, if only configuration data can be used
>> to create the output version string, probably this version string can be
>> checked by the system before starting the job and not produced and checked
>> per document because basically all the documents are going to produce the
>> same exact output version string. Probably I'm missing something but, for
>> example, looking at Tika Transformation connector seems to be pretty clear
>> that there would be no difference between output version strings for all
>> the documents because it is using only configuration data to create the
>> string.
>>
>> 3.In the addOrReplaceDocumentWithException, why is the
>> pipelineDescription passed by parameter instead of the connector
>> Specification to ease the developer to access the configuration without
>> marshalling and unmarshalling it?
>>
>> 4. Is there a way to reuse a single configuration object per job
>> execution? In the Output processor connector, I used to initialize my
>> custom stuff in the connect method (I'm not sure if this strategy is valid
>> anyway), but for the Transformation connectors I'm not even sure if this
>> method is called.
>>
>> Thanks a lot for your help beforehand. Please note that the questions of
>> course are not intended to be criticism. This mail is just a dump of doubts
>> that probably will help me to better understand the workflows in manifold
>>


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