objects in cache torage

[denny]

Hi,

I am pretty new to OD. we are running od8.5 on Aix 6.1.
I am finding below objects and want to know more location information about the details.

lrwxrwxrwx    1 root     system           42 Nov 05 15:21 543330FAA1 -> /arscache/cache04/16096/HAA/DOC/543330FAA1
lrwxrwxrwx    1 root     system           42 Nov 05 15:21 543330FAAA -> /arscache/cache04/16096/HAA/DOC/543330FAAA

These 2 objects are in retrieval area and linked to real object. I want to know how OD manager the objects in cache storage. Say in our case, we have 4 FS created for cache storage, how OD decided to place the object in which FS and what is the meaning of subdirectory 16096? where OD get this information? The real object is 543330FAA, Why we are seeing 543330FAA1 and 543330FAAA, what is purpose?

I understand the HAA and DOC meaning.

Thanks,
Denny

[Justin Derrick]

Hi Denny.

It looks like you're inside the "retr" directory.  Inside this directory are a series of subdirectories that refer to the individual Application Groups.  These links point to the individual items stored inside the cache, possibly on other filesystems.  This is how CMOD retrieves documents quickly.  Think of it as an 'index' that points directly to the documents, no matter where they exist on the system.

As for how CMOD assigns documents to cache filesystems, we don't have access to the source code (so that we would know for sure) but it seems like CMOD puts documents into caches with the most free space first.

While it's nice to know this information, the cache manages itself quite well, as long as you're running arsmaint on a regular basis -- so there's usually no need to worry about how CMOD manages it.

-JD.

[denny]

Hi Justin,

Thanks for quick response to my question.

I have been looking for certain information for few days without luck. There is no table referring to the location information. That is why i am curious to know how OD knows the location, once user try to retrieve the document, how OD finds it.

Do you have any idea about my second question regarding the file name?

The real object is 543330FAA, Why we are seeing 543330FAA1 and 543330FAAA, what is purpose?

Denny

[swat_is_back]

Hi Denny,

The file with 1 at last is having the metadata and the one with A at last is the actual object (may be compressed if you used the compression settings like OD77/OD77Lite etc).
these is no purpose of having 1 (as far as I know) but these files would help you if something bad happens with your database and you want to regenerate the database.

Hope this helps !!!

Thanks,
Swat

[Justin Derrick]

Yup, Swat is definitely correct, especially about the compression and using the FAA1 files to recover data.

There isn't a database table with location info, because CMOD knows that all data is in one of two places:  In the cache, or in TSM.

When someone tries to retrieve a document, CMOD looks inside the RETR directory in the cache to see if there's a link to the data object it's looking for.  If there is no link, it goes to TSM to ask for the data.  If CMOD *does* find a link, it uses the link to have the operating system open the file, and CMOD reads the contents, and sends it to the user.

I hope that helps!

-JD.

[denny]

thanks Swat and Justin, it is now more clear to me.

Regards,
Denny