Author Topic: Remove cache filesystem entry from ars.cache file  (Read 1911 times)

Mani

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Remove cache filesystem entry from ars.cache file
« on: November 12, 2015, 01:15:56 AM »
Hi All,

We have seen some performance degradation after adding the new cache filesystem's entry (cache4) into the CMOD ars.cache file

before adding cache4 ( 2 days back) , the arsload was running very fast, but after the addition of it, it has gone down by more than 60%. we have sufficient space in cache2 and cache3 to accomodate the daily loads. so, the past 2 days, the daily loads are happening in cache4 only. so, I want to remove the cache4 entry in the ars.cache file to prevent any files from being written, will it have any impact on the retrieval of the documents loaded in the last 2 days under cache4

/cache1
/cache2
/cache3
/cache4


We are useing below

CMOD V 9.5.0.2
DB2 V 10.7
Cache only solution ( No TSM)




thanks
Mani

Alessandro Perucchi

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Re: Remove cache filesystem entry from ars.cache file
« Reply #1 on: November 12, 2015, 02:09:47 AM »
Hello Mani,

wow you already have DB2 V10.7 :) you are on the beta version program? :D Just kidding :) I think you wanted to say 10.5.7!

That aside, you can simply remove the entry in the ars.cache file for your /cache4 directory, and that's it.
CMOD won't add new files on it, and it will still be able to retrieve the documents back from /cache4 (normally... but you should check in test before doing it in Prod, because you need also to restart CMOD to refresh that information)
the verification of the cache will complain a lot! :-)

I know that CMOD does a LOT of checks on the directory, so maybe it won't be able to retrieve the document in the cache after you remove the entry in ars.cache.... that's why you need to test in your test environment.

The idea behind is that /cache1/retr/ contains all the links to the files in the cache filesystems, so you won't loose anything.

Now why does CMOD write only in /cache4, and not spreading in all the other FS too?
CMOD use a kind of round robin algorithm, that look at the disk space (percentage)  available for each cache filesystem.
If he sees that one is nearly empty, then he will prioritize this filesystem, and use only this one, until it reaches the same percentage level of the other cache filesystem.

Maybe a reshuffling of all files in the cache to rebalance the directories would be a good idea... (maybe an improvement request for CMOD Developers :) ) That reshuffling is today not available, and can be done "manually" if you understand how the cache works. Of course, this needs to be tested before doing anything in production!! :-)

I hope that helps in understanding what happened in your system.
« Last Edit: November 12, 2015, 02:13:38 AM by Alessandro Perucchi »
Alessandro Perucchi

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Mani

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Re: Remove cache filesystem entry from ars.cache file
« Reply #2 on: November 12, 2015, 05:52:24 AM »
thanks Alex for the quick response.


thanks
Mani