Advise on ClassIndicator, using an integer

Question

Hi all,
the default ClassIndicator is in-class-name which generate a jdoclass column
with the entire classname string in it. If this would be an integer field,
it would not only save quite some storage space, but I assume would also be
better in performance. My questions:
- Does anyone have experience with this and if so, is there a noticable
performance increase?
- If I would use the Metadata Value Indicator, does this mean that I need to
mannually add an in integer column to each class in the .mapping file and
specificy the integer value for each class in the .jdo file, next to summing
up all classes in the kodo.PersistenceClassList?
- The manual writes about a custom class indicator. It mentions an example
in the ormmapping directory, but I cant really find this. Would it be
difficult to write an indicator that uses integers and works just like the
in-class-name indicator, so without manual intervention. I assume it would
be best to subclass InClassNameClassIndicator where I maintain a map of
class to integers?
kind regards,
Christiaan

Answer 1

Hi Dave,
I succeeded in creating an IntegerClassIndicator which was actually pretty
easy to do. Thanks for the info!
"Dave" <[email protected]> wrote in message
news:[email protected]...
Hi Christiaan,
I agree, it would be good to have a class extension that allows one to
specify the column name for metadata-value class indicators. I've
entered your suggestion as a feature request in Bugzilla at
http://bugzilla.solarmetric.com/show_bug.cgi?id=1232
As to the performance concern, I would not worry too much about it,
unless you have metrics that indicate that it is a problem. The
DataCache can boost performance a great deal (assuming that you use
optimistic transactions). Any hit that you take from overly long keys
is not likely to be significant.
As a rule of thumb, try to avoid early optimization unless you're
implementing a low cost, high probability optimization, a.k.a. "a best
practice."
Best wishes,
David
On Wed, 30 Nov 2005 10:48:01 +0100, "Christiaan" <[email protected]>
wrote:
Thanks for the answer Dave. I am actually not really keen on explicitly
tweaking the Mapping file, I'd rather have this entirely generated by
kodo.
I also noticed that the DataCache used the same combination of classname +
'' - " + id as a key for identifying objects, which is a pretty huge
string
which doesnt make it really performant in a HashMap. Do you know if these
two are related? So if I change the indicator to integer, the DataCache
will
use that same integer as a key.
Btw, do you know of any example of implementing a custom ClassIndicator?
"Dave" <[email protected]> wrote in message
news:[email protected]...
Hi Christiaan,
First of all, you can specify "none" as the jdbc-class-ind-name value
for any classes that are not part of an inheritance tree of data
classes. The indicator is only needed when the information loaded
from the database comes from a table (or tables) that store state for
more than one class. You can't get any faster than not having it at
all!
Second, if you use the MetaData indicator (value for
"jdbc-class-ind-name" is "metadata-value"), then you specify in the
mapping file the column in the db table that will have the indicator
constant. This works very much like the in-class-name indicator,
except that you associate a name (of your choosing) with the class in
the metadata, and you have to explicitly tweak your mapping file. See
the example in the doc at
http://www.solarmetric.com/Software/Documentation/latest/docs/ref_guide_mapping_classind.html#metadata-value
Hope this helps,
David Ezzio
If you use the Meta
On Fri, 25 Nov 2005 15:05:00 +0100, "Christiaan" <[email protected]>
wrote:
Hi all,
the default ClassIndicator is in-class-name which generate a jdoclass
column
with the entire classname string in it. If this would be an integer
field,
it would not only save quite some storage space, but I assume would also
be
better in performance. My questions:
- Does anyone have experience with this and if so, is there a noticable
performance increase?
- If I would use the Metadata Value Indicator, does this mean that I
need
to
mannually add an in integer column to each class in the .mapping file
and
specificy the integer value for each class in the .jdo file, next to
summing
up all classes in the kodo.PersistenceClassList?
- The manual writes about a custom class indicator. It mentions an
example
in the ormmapping directory, but I cant really find this. Would it be
difficult to write an indicator that uses integers and works just like
the
in-class-name indicator, so without manual intervention. I assume it
would
be best to subclass InClassNameClassIndicator where I maintain a map of
class to integers?
kind regards,
Christiaan