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This is really great

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jfbriere
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Joined: 2003-07-29
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First I want to thank Sun for this JQS feature.

It works pretty smooth on Windows 2003 and also on XP (both witth Firefox 2 and IE 7 or 6).
I think it's an important milestone in the Java client evolution ( or revolution :-) ).

Just curious about one thing.
It is said that JQS is : "periodically prefetching some of the most heavily used Java Runtime Environment files into memory".
Although I executed many Java applications, webstarts or applets I failed to see in the task manager the jqs.exe memory usage going more than 1.5 Mb.

Which files are typically prefetched?

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jmelvin
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Joined: 2004-12-01
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>> Which files are typically prefetched?

Actually, JQS will prefetch select page ranges from JRE files. The JQS config file controls
what pages/files are prefetched...

${JRE}/lib/deploy/jqs/jqs.conf

This config file is custom tuned for the JRE with which it is shipped. So, it may be invalid
for any other JRE, etc.

linuxhippy
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Joined: 2004-01-07
Points: 0

> Just curious about one thing.
> It is said that JQS is : "periodically prefetching
> some of the most heavily used Java Runtime
> Environment files into memory".
> Although I executed many Java applications, webstarts
> or applets I failed to see in the task manager the
> jqs.exe memory usage going more than 1.5 Mb.

Well I guess jqs just reads the files from time to time - which indicates the OS that these files tend to be read more often and are therefor cached. So the files are stored in the OS cache, not in memory regions allocated by jqs.

lg Clemens

weiqigao
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Joined: 2003-06-10
Points: 0

> Well I guess jqs just reads the files from time to
> time - which indicates the OS that these files tend
> to be read more often and are therefor cached. So the
> files are stored in the OS cache, not in memory
> regions allocated by jqs.

Just reading this answer made me think if other libraries could also use the same strategy to speed up their startup time. And if too many of such services are present in a system, eventually they will be competing against each other for the limited resource of the OS file cache.

I don't think this is a problem now. And I don't know if it will become a problem in the future.

Another category of applications that reads files on the disk periodically is the desktop indexing appls (Google or Yahoo or Microsoft Desktop Searches). I wonder how well JQS plays with them.

jmelvin
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Joined: 2004-12-01
Points: 0

>> if too many of such services are present in a system, eventually they will be competing
>> against each other

Indeed. If all applications employed a prefetcher, they would all run into each other.
It's not a problem now, but no guarantees for the future. JQS does have some throttling
implemented for various system metrics. So, we prefetch only when conditions are
amenable.