For paginated queries we contemplated a strategy of a list with
constant size of fully resolved objects. I.e. when a page is swapped
in, some other (LRU?) page is swapped out. We decided against it, as
in a general case it is hard to consistently predict which page should
be swapped out.
However it should be rather easy to write such a list for a specific
case with a known access order (e.g. a standard iteration order). In
fact I would vote to even include such implementation in Cayenne going
forward.
More specifically, you can extend IncrementalFaultList [1], overriding
'resolveInterval' to swap out previously read pages, turning them back
into ids. And the good part is that you can use your extension
directly without any need to modify the rest of Cayenne.
Andrus
[1]
http://cayenne.apache.org/doc/api/org/apache/cayenne/access/IncrementalFaultList.html
On Nov 12, 2009, at 10:07 AM, Hans Pikkemaat wrote:
Hi,
So this means that if I use a generic query that the query results
are always stored
completely in the object store (or the query cache if I configure it).
Objects are returned in a list so as long I have a reference to this
list (because I'm
traversing it) these objects are not garbage collected.
If I use the query cache the full query results are cached. This
means that I can only
tell it to remove the whole query.
Effectively this means I'm unable to run a big query and process the
results as a stream.
So I cannot process the first results and then somehow make them
available for
garbage collection.
The only option I have would be the iterated query but this is only
usefull for queries
one 1 table without any relations because it is not possible to use
prefetching nor is
it possible to manually construct relations between obects.
My conclusion here is that cayenne is simply not suitable for doing
large batch wise
query processing because of the memory implications.
tx
HPI
Andrus Adamchik wrote:
As mentioned in the docs, individual objects and query lists are
cached independently. Of course query lists contain a subset of
cached
object store objects inside the lists. An object won't get gc'd if it
is also stored in the query list.
Now list cache expiration is controlled via query cache factory. By
default this is an LRU map, so as long as the map has enough space to
hold lists (its capacity == # of lists, not # of objects), the
objects
won't get gc'd.
You can explicitly remove entries from the cache via QueryCache
remove
and removeGroup methods. Or you can use a different QueryCacheFactory
that implements some custom expiration/cleanup mechanism.
Andrus
On Nov 11, 2009, at 3:43 PM, Hans Pikkemaat wrote:
Hi,
I use the latest version of cayenne, 3.0b and am experimenting with
the object caching features.
The documentation states that committed objects are purged from the
cache because it uses weak references.
(http://cayenne.apache.org/doc/individual-object-caching.html)
If I however run a query using SQLTemplate which caches the objects
into the dataContext local cache (objectstore),
the objects don't seem to be purged at all. If I simply run the
query dump the contents using an iterator on the resulting
List then the nr of registered objects in the objectstore stays the
same (dataContext.getObjectStore().registeredObjectsCount()).
Even if I manually run System.gc() I don't see any changes (I know
this can be normal as gc() doesn't guarantee anything)
What am I doing wrong? Under which circumstances will cayenne purge
the cache?
tx
Hans
--
<tsi_logo.png>
TSi Solutions
Neptunusstraat 25
7521 WC Enschede
Tel. +31 (0)88 - 25 00 000
Fax. +31 (0)88 - 25 00 122
Hans Pikkemaat
Java Developer (Services Team)
E-mail: [email protected]
www.tsi-solutions.nl
www.toeristiek.nl
<tsi_sunset.png>
<tsi_pictos.png>
10 jaar TSi Solutions
... marktleider in het automatiseren en outsourcen van werkprocessen
in de reisbranche
... toonaangevende partij voor het verzamelen, structureren en
beschikbaarstellen van reiscontent
... Reisrevue Innovatieveer 2008 - Veervolle vermelding
... Winnaar Reisrevue Innovatieveer 2009
... Top 20 positie in 2008 Deloitte Technology Fast50 Nederland
... Top 10 positie in 2009 Deloitte Technology Fast50 Benelux
... genomineerd voor Technology 500 EMEA 2009
TSi Solutions is de handelsnaam van Travel Service International b.v.
[KvK 06091935]
DISCLAIMER: De informatie opgenomen in dit bericht kan vertrouwelijk
zijn en is uitsluitend bestemd voor de geadresseerde.
Indien u dit bericht onterecht ontvangt, wordt u verzocht de inhoud
niet te gebruiken en de afzender direct te informeren door het
bericht te retourneren.
The information contained in this message may be confidential and is
intended to be exclusively for the addressee.
Should you receive this message unintentionally, please do not use
the contents herein and notify the sender immediately by return e-
mail.
