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From "Cristian">
Subject Re: heap size problems (speed) [2]
Date Mon, 28 Nov 2005 19:21:07 GMT
> I don't think your CPU L caches are going to influence
> the issues you are seeing...not noticeably..not with
> todays hardware.  Cristian is resizing the java heap
> to allow it to get larger than it was able before
> (default or the Tomcat default setting).  In this case
> heap being the amount of memory the java process is
> going to be able to use for the process aside from the
> static space which can not be controlled by the heap
> setting being used.
> How much memory does your computer physically have
> Cristian?  Are you also using -Xms512m?  I'll wait to
> here about your memory first before making other
> comments on that.

1G of RAM and I do not set -Xms512m
swap space is hit ocasionaly but not all the time.

> The next thing I'm going to ask deals with another
> issue we had on the list.  Do you also write to the
> HashMap from your application?  Are you reading and
> writing to this cache or your application loads this
> cached data at start up and it is merely read from
> that point on?  If you are writing to this data you
> need to be sure to synchronize the HashMap because if
> you don't you can get into some serious problems with
> concurrency issues and HashMap resizing (synchronize
> reads and writes).  If you load all of the data up
> then only read from the application then synchronizing
> the reads to the hash map won't matter (unless you
> allow reading while the loading is occuring).

The application only caches data at startup and after that it performs
only read operations regarding this cache.

> The next question would be: Even if only reading and
> you are are currently synchronizing the calls to this
> "cached" data are the operations long?  If the
> operations to a synchronized resource are very long
> then other threads (requests in this case) will be
> delayed while trying to access the HashMap.

I'm told that the accesses are not "long ones" ... The designer of this
just  accesses the HashMap. If it exists, OK they return the value.
If not they return the name of the requested key.

Please don't blame my lack of knowledge in this matter, this being only
what they've told me.
I am far away (hundreds of pages of java docs) from understanding the
I'm only providing support on linux for tomcat (installation with APR
They wanted to test this scenario on linux because on windows they claim
it worked.

However I can understand advises and put them into practice if needed.
Also, as I said before, I am able to read some docs that would
eventually get me to the point of solving and understanding the problem.

> Wade


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