|
| Re: [CDO] using the query interface [message #423355 is a reply to message #423342] |
Mon, 29 September 2008 12:38   |
|
Stefan Winkler schrieb:
> Hi,
>
> over the weekend I thought about ways to speed up my application.
> One of the features of CDO is that it can load only the parts of a
> model which are needed. However at the same time every access to a
> non-cached object results in a DB query. I thought, I could speed up
> the process of reading a larger part of a model by pre-caching it.
> E.g. if there was a way to load an CDO object from the database and
> all of its containments (children) up to a certain depth (IOW the
> object O and off of O.getCildren() and all of O.getChildren().each { c
> -> c.getChildren() } , I could pre-load a complete tree in one operation.
You might also want to look at some other new features to optimize the
characteristics. Have a look at the attached document in:
245654: Provide a "Tweak Performance" tutorial
https://bugs.eclipse.org/bugs/show_bug.cgi?id=245654
Maybe you're able to develop (and contribute?) a special
CDOFeatureAnalyzer...
> Then I came in this morning and I thought, well, there once was a
> proposal for a CDO query feature and I found out that the bug is
> closed already.
>
> So,
>
> 1. Is the CDO query interface usable?
If I take the question as it's written, I'd say yes. The API is new but
carefully chosen. But you'll have to provide a query language name that
is implemented either by the backend store (i.e. IStore of CDO) or the
repository itself. And currently only a test language is supported by
the MEMStore and a simple "query resources" language by all
repositories. In other words, the query feature is an extensible
framework rather than a complete set of implemented query languages. It
provides simple service provider interfaces for developers of backend
query languages or repository-level query languages (including an
extension point), as well as a convenient client API to work with
synchronous and asynchronous queries.
> 2. Which query language do you support?
See above. We are looking for help with the implementation of additional
query languages. There are currently three obvious ones on the wish list:
244169: [Hibernate] Store to support Query (HQL)
https://bugs.eclipse.org/bugs/show_bug.cgi?id=244169
248933: [DB] Support SQL as a CDOQuery language
https://bugs.eclipse.org/bugs/show_bug.cgi?id=248933
245658: [Query] Provide OCL query language
https://bugs.eclipse.org/bugs/show_bug.cgi?id=245658
> 3. Is the native mysql DBStore supported?
See above.
> 4. Does one query really lead to one DB-select operation (i.e. is the
> query translated to SQL and executed at DB level) or is the query
> evaluated and executed at the CDO server resulting in single
> DB-operations for reading revisions one by one?
It's left completely to the backend query language implementor how a
query translates into backend primitives. Since repository-level queries
are expected to run against the server-side RevisionManager it's likely
that they will not be optimized for certain backend types. If SQL was
provided as a DBStore-level query language I don't see a problem in
backing a query by a single SQL statement.
Cheers
/Eike
>
> Thaks in advance for your answers!
>
> Cheers,
> Stefan
>
>
>
>
Cheers
/Eike
----
http://www.esc-net.de
http://thegordian.blogspot.com
http://twitter.com/eikestepper
|
|
|
|
| Re: [CDO] using the query interface [message #423363 is a reply to message #423361] |
Mon, 29 September 2008 14:41 |
|
Stefan Winkler schrieb:
> Hi Eike,
>> You might also want to look at some other new features to optimize
>> the characteristics. Have a look at the attached document in:
>>
>> 245654: Provide a "Tweak Performance" tutorial
>> https://bugs.eclipse.org/bugs/show_bug.cgi?id=245654
>>
>> Maybe you're able to develop (and contribute?) a special
>> CDOFeatureAnalyzer...
> Mhhh ... thanks for the pointer. Interesting read ...
> But I think there is a basic problem around here:
>
> org.eclipse.emf.cdo.internal.server.RevisionManager:
>
> @Override
> protected List<InternalCDORevision> loadRevisions(Collection<CDOID>
> ids, int referenceChunk)
> {
> IStoreReader storeReader = StoreThreadLocal.getStoreReader();
> List<InternalCDORevision> revisions = new
> ArrayList<InternalCDORevision>();
> for (CDOID id : ids)
> {
> InternalCDORevision revision =
> (InternalCDORevision)storeReader.readRevision(id, referenceChunk);
> revisions.add(revision);
> }
>
> return revisions;
> }
>
> In my opinion the IStoreReader should support reading multiple
> revisions at once.
> My guess is that prefetching revisions one by one does not provide
> much performance gain (well, at least as long as I use the
> jvm-Connector...). What really should drive performance would be
> reducing single database accesses and batch them together.
> So, instead of
> - select ... from ... where cdo_id = 214 and cdo_version = 4
> - read answer
> - fill in revision
> - select ... from ... where cdo_id = 215 and cdo_version = 4
> - read answer
> - fill in revision
> - select ... from ... where cdo_id = 216 and cdo_version = 4
> - read answer
> - fill in revision
> it should be much more efficient to implement a way to
> - select ... from ... where (cdo_id = 214 and cdo_version = 4) or
> (cdo_id = 215 and cdo_version = 4) or (cdo_id = 216 and cdo_version = 4)
> - read answer
> - fill in revisions
>
> However, I see several challenges here :-(
> - the current IDBStore implementation might be hard to enhance because
> of the single-sql-string-builder
This seems to be a minor technical challenge, but...
> - the above works only for objects of the same type - what if we use
> polymorphism in the list?
.... this one was also my first thought. A more conceptual issue and
probably a real problem ;-)
I have no idea how to solve this and a solution without considering
polymorphism is not appealing.
> - ...
>
> Anyway, do you want an enhancement request filed? "Support fetching of
> multiple revisions at once in IStoreReader"?
I think it would make sense to discuss if the protocol between
RevisionManager and IStoreReader can be optimized in general (still with
respect to reading multiple revisions at once). But I doubt that the
DBSore with its horizontal mapping strategy will particularly benefit
from it. Would you like to come up with a contribution for all this?
Cheers
/Eike
Cheers
/Eike
----
http://www.esc-net.de
http://thegordian.blogspot.com
http://twitter.com/eikestepper
|
|
|
|
| Re: [CDO] using the query interface [message #423417 is a reply to message #423416] |
Tue, 30 September 2008 09:27 |
|
Stefan Winkler schrieb:
> Hi,
>>>
>>> Anyway, do you want an enhancement request filed? "Support fetching
>>> of multiple revisions at once in IStoreReader"?
>> I think it would make sense to discuss if the protocol between
>> RevisionManager and IStoreReader can be optimized in general (still
>> with respect to reading multiple revisions at once). But I doubt that
>> the DBSore with its horizontal mapping strategy will particularly
>> benefit from it. Would you like to come up with a contribution for
>> all this?
> I feared you would ask for this ..
> Like? yes
> Have time? regretfully no :-( - at least not right now :-(
I feared you would say for this .. ;-)
Cheers
/Eike
Cheers
/Eike
----
http://www.esc-net.de
http://thegordian.blogspot.com
http://twitter.com/eikestepper
|
|
|
|
Powered by
FUDForum. Page generated in 0.02120 seconds
Search
Help
Register
Login
Home
