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From yarono <yar...@il.ibm.com>
Subject Derby db - need to disable improved performance
Date Tue, 22 May 2007 15:01:15 GMT


I'm working on a simple db. Each record is composed of 3 long values. The
first two are the primary key.

I have to measure the performance of the insertions. Each insertion is
wrapped in a transaction, which is commited having only one insertion in it.
I've measured both berkeley db performance and postgres and got about
110-115 insertions per second.

Now in derby db (both in embeded mode and server mode) I get better
performance: about 250-300 insertions per second. This obviously results
from some kind of a group commit, although I get these results both when
auto-commiting or manual-commiting after each insertion.

I've performed a simple test of synchronious writing 24 bytes (3 * 8 bytes)
to the disk. It measure 117 writes per second, and I believe this is the
upper bound of any db performance.

So, I don't understand why I get such good performance, although I commit
after each insertion.

I examined the .dat files in both /log and /seg0 folders. None of them
increase in 24 bytes segments, but rathar bigger segments.

So, my questions are:
1. Which log file in /log or /seg0 should I examine to analyze the numebr of
bytes written each write to disk?
2. How do I disable the group commit or whatever attribute that causes this
communal write? how do I make each transaction be written on its own to the

Thanks in advance,
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