performance stories

technical essays about performance, life and everything ;)

Month: July, 2012

A couple of thoughts about Hibernate, caches and OQL

I was needed to clarify several things on Hibernate according to my work (what is a query cache? does it have regions? what is update timestamps cache? does it have regions or not?)

In general, there is a lot of articles, papers, notes, manuals, etc. One of the excellent examples is http://tech.puredanger.com/2009/07/10/hibernate-query-cache/.

So we got some understanding on query cache and update timestamps cache after reading: there is a query cache with query and bound variables as keys and update timestamps cache, that keeps a record corresponding to each table (was it modified or not later than query result was cached).

ok, I decided to see that with my own eyes

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How to speed up java heap dump generation…

As you know, we need memory dump for a lot of things: memory leak analysis, memory footprint analysis (high memory footprint could be a problem sometimes) and to check/understand some details about our application.

However, in some circumstances heap dump generation can last tens minutes or even more. And all this time application is not available (yeah, we could set up a cluster, of course, but sometimes, it isn’t done). So that was my case, a server, which I had to get a memory dump from, was not clustered, heap size was about several gigabytes, jmap was used (jmap –F –dump:format=b…..), dump was stored to disk.

Next simple ideas helped me speed up dump generation more than 10 times:

read about ideas

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