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From Bryan Pendleton <bpendleton.de...@gmail.com>
Subject Re: Could use some thoughts on a problem with a query in production
Date Tue, 06 Jun 2017 13:28:02 GMT
Hi Brett?

What's the underlying storage system like? In particular, is it an SSD
storage system? Is there any chance that you happened to hit a spot
in time where there was some non-Derby event which was causing the
storage system to misbehave?

I understand that certain SSD implementations, and certain file
systems, have to perform automatic maintenance activity on the
SSD media, such as "wear leveling", which can impose significant
overhead on the file system and cause normal use of the file system
to be VERY slow for a significant period.

Here's a relatively old article on the subject; you might try some web
searching
to see if you can get more recent information.

http://www.computerworld.com/article/2524589/data-center/analysis--ssd-performance----is-a-slowdown-inevitable-.html

Anyway, I guess what I'm suggesting is that you consider investigating
whether a non-Derby external factor is at work on the machine which
is suffering the performance problems.

thanks,

bryan

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