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From The Wogster <wogste...@yahoo.ca>
Subject Re: Behaviour of SYSCS_COMPRESS_TABLE
Date Thu, 02 Jun 2005 13:38:18 GMT
Mike Matrigali wrote:
> The split description below describes Derby behavior.
> Derby does not merge "almost" empty pages - only empty pages.
> Derby maintains a separate file per table and a separate file
> per index.  Derby maintains a free page pool per file and only
> can use the free pages in the same file to fill space requests.
> 

I was talking in generalities, each specific database works differently, 
   some store the entire database in a single file, like Firebird does 
others store each table in a file, like PostgreSQL does, and others 
store each item in a separate file, as it appears Derby does.

Personally I don't think it really matters, if your compressing a 
database to save space, then there is a bigger issue, like too small a 
hard drive.  Back in the days when $10,000 would buy you 10MB of storage
(roughly 1,000,000 per GB) saving space was a big deal, now, when $100 
buys you 100GB ($1 per GB) it's often a false economy to waste the time 
fussing with it, just to save disk space, especially when the guy doing 
the fussing is worth $40/hour.  Compression should be used because it's 
good for the database, not to save disk space.

It also ends up being a false economy, unless the database is static, 
because your just going to start adding to it again, and extending a 
file, typically means a kernel request, and that is going to be much 
slower then simply adding a page in the file already.


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