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From "Jim Newsham" <jnews...@referentia.com>
Subject excessive disk space allocation
Date Mon, 20 Oct 2008 22:32:01 GMT



I'm doing some benchmarking of our application which stores data in derby.
The parts of the application which I am exercising only perform inserts, not
deletes.  The results suggest that derby disk space allocation is excessive,
particularly because compressing the tables reduces the size of the database
*substantially*.  For example, here are the results of several databases,
both before and after compression.  


Application running time.  original -> compressed

0.5 days.  178.2mb -> 63.1mb

1 day.  559.3mb -> 82.8mb

2 days.  1,879.1mb -> 120.8mb

4 days.  5,154.4mb -> 190.5mb

8 days. 11,443.7mb -> 291.6mb

16 days.  23,706.7mb -> 519.3mb


Plotting the data, I observe that both uncompressed and compressed sizes
appear to grow linearly, but the growth factor (slope of the linear
equation) is 53 times as large for the uncompressed database.  Needless to
say. this is huge.


I expected that with only inserts and no deletes, there should be little or
no wasted space (and no need for table compression).  Is this assumption





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