Re: FNDSTRPDM memory enhancement -- MIDRANGE-L




Thanks Mark!  Your detailed explanation really helps me understand the
whole process.
Now I am scared.  Programmers can run FNDSTR anytime to batch.  Depending
on what they want to search, the program could read through every source
member on the system scanning for that string.  What I didn't realize
before though was that this program running would cause every member
"touched" to be paged into real main storage.  The development system is
separate from production but still we could contend with each other.  Even
someone running the FNDSTRPDM as opposed to FNDSTR where they pick a large
library to search could page important jobs when finding a string.
The job to page all these members (using SETOBJACC) to main memory would be
running very early in the morning when no one is here.  That might not help
though if other jobs later page on top of these.  So, that is probably not
a good option as you mentioned.  Actually, now I would like to keep from
paging these members to main memory.  We probably just have to make sure we
run the FNDSTR as maybe a scheduled job or realize it will slow down the
system.  Or, better yet, as you suggested, submit the FNDSTR to a separate
memory pool.  How might I do this?  I could make the pool ridiculously
small so as not to contend with other jobs as it runs.  Expert Cache sound
interesting but it must have its drawbacks.

Thanks,
Craig

** Mark wrote:
Hi, Craig:

OS/400 uses a single large virtual address space or "single level" storage.
In this scheme, real main storage is truly just a "cache" of the most
recently
used "pages" of objects recently "touched" (used, read or written to).

So, based on the above, I suspect that what is really happening is,
the first time you run FNDSTRPDM, it "touches" these members,
and their contents are paged into real main storage.  If your system
is not too "busy" and you have lots of main storage, then there is
nothing to force those pages to get paged out ("stolen"), and so,
the next time you run FNDSTRPDM over the same source files
(set of members), you notice that it seems to run much faster.

Unless you have vast amounts of real main storage, I do not think
it would be a "good idea" to submit jobs to read every member,
thus attempting to page them all into real main storage. At some
point, you will exceed the total amount of real main storage and
this will start to force out other pages, which could be pages for
other "production" jobs and users, who may really need that data,
and so, you could have a major negative impact on the overall
performance and throughput of your system...

You could create a separate memory pool, and then run your
RPG program that opens and reads all the members, and run that
batch job in a subsystem that uses only that one memory pool; that
might speed things up... and at least, this way, you limit the total
amount of real main storage that you will use, to just that one
memory pool.  But, the whole time you have this memory pool
allocated to a particular subsystem, no one else can use it.

So, you are probably best off to just let OS/400 take care of
itself... OS/400 also has something called the "Expert Cache"
that you can enable... for a given storage pool... that might
help, too...

Unfortunately, as far as I can tell, SETOBJACC only works
one member at a time, so you would have to issue SETOBJACC
for each member, and there are probably too many members in a
single source file to all fit into one memory pool at a time anyway,
so that would sort of defeat the purpose...

Hope this helps...

Regards,

Mark S. Waterbury