Re: Object query language?

[William Uther <will+ozone-db@cs.cmu.edu>]

--On Saturday, March 18, 2000 4:51 PM +0100 Falko Braeutigam 
<falko@softwarebuero.de> wrote:

> You can use any collection classes in ozone. In fact, ODMG collections
> have exactly the same interface as java.util collection.

I agree.  I was expecting the ODMG and normal collections to have slightly 
diferent semantics however.

Normal collections are loaded into memory as a block.  They cannot be any 
larger than available RAM on the server.  This is exactly the reason that 
Ozone uses a disk based map for it's index.

I was expecting the ODMG collections to be disk based and hence of 
arbitrary size.

> Is this the reason that let you try to use proxies as keys, Will - avoid
> to store the key value twice if it is also a direct attribute?

I guess you could view it that way.  (In my case the key is not an 
attribute.  The key is a value calculated using the attributes.  A separate 
key would not be a duplicate of the attributes, but a cache of the 
calculated value.)

> In most cases it should
> be no problem to sync the index with the attribute values of the indexed
> objects.

It is not too much extra work.  It would complicate the code though.

> This
> is much faster *and* less space consuming (although you avoid doubling
> the key) than haveing millions of 10 byte objects stored in the database.

In my case the objects used as keys are already proxied objects.  I 
wouldn't be saving on the number of proxied objects.

The big speed hit is going to be when loading or unloading the hashtable 
from memory, not accessing it once in memory.  The extra work of creating 
the cache object is going to eat up advantage you might have during normal 
operation.

In terms of storage space, we are comparing an extra proxy (referencing an 
already proxied object) to a new object duplicating a pair of strings each 
up to 100 bytes long (say 30 bytes average).  (I moved from chars to lines 
of text because char-by-char compression was too slow.)  I would be 
extremely surprised if the extra proxy was costing me 60 bytes in storage.

later,

\x/ill            :-}