determining class sizes

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by johnmunro >> Fri, 30 May 2003 12:27:20 GMT

I'd like to write a jadescript that you pass a Class and which displays the number of bytes that instances of this class will take up in the database. Basically I'm sick of people asking me how much space a system with x million instances of class y will take up, because I can never remember all of the rules about collections and oid lengths and headers etc.

Has anyone done anything like this? Is there a reference anywhere of this information? I remember seeing parts of the information I need scattered about the pdf files, but I was hoping someone had collected it all somewhere...


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by allistar >> Sun, 1 Jun 2003 7:57:20 GMT

Hi John,
One of the pdf files (can't remember the exact one, but from memory it is the one that contains the JOMAPI reference) spells out how much space is taken up by each property type, and also byt the object headers.

You could write a script that iterates through all properties on a class and based on the sizes found in the aforementioned pdf you could sum them up and mutliply by the number of objects.

I don't think it spells out how many bytes each collection block takes up, and I don't know that you would be able to tell how many blocks a collection will have based on the number of objects in it. For not many objects it wouldn't make much difference but have a collection with 10,000,00 would take up a noticable amount of space.

The other way is to set the intial file size and file growth increment in the ini file to a small number and then create a million objects and see how much space is taken.

Regards,
Allistar.

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by Patwos >> Tue, 3 Jun 2003 2:28:47 GMT

Further to Allistar's message, if you run a certify of the mapfile containing instances of the class in question you can find out how large each instance is in bytes. Of course, if you have exclusive subobjects, including Slobs and Blobs, then it won't be a complete picture either but good luck to you working out how large a million instances will be if each instance contains an unknown amout of Slob/Blob data.

Pat.

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by cnwjhp1 >> Tue, 3 Jun 2003 3:40:11 GMT

For help with collection info, check out Dictionary::getStatistics():String (undocumented and unsupported for 5.2 I believe; moved to Collection class for 6.0) and CollClass::maxBlockSize.

Cheers,
John P