DB2 Data Links Manager Quick Beginnings

Workarounds in NFS environments

This section describes workarounds to known problems when running DB2 Data Links Manager for AIX in NFS environments. These problems are NFS-specific and have nothing to do with DB2 Data Links Manager or DB2 Universal Database.

Access tokens may not expire as expected

If you are using an NFS client to access files, you may find that the access token does not expire appropriately. This can be due to caching done by the NFS client. Using file names greater than 12 characters may solve this problem.

Client-side file permissions do not reflect changes after a file is linked

NFS client-side file permissions may not immediately reflect changes after a file is linked on the server with READ PERMISSION DB. This delay is due to attribute caching done by NFS. As a result, file permissions may appear to be different on the client. These cached attributes have an expiry time limit after which they are automatically invalidated. After expiration, file attributes are obtained from the server on the next access.

File appears to be readable without a valid access token

When a file is first accessed by a user from a NFS client, the directory name lookup entry is cached in NFS. Subsequent lookups of the file by the same user from the client are serviced from this cache. If the file is then linked on the server, that user will still be able to open the file with READ PERMISSION DB, and the newly linked file may appear to be readable without a valid access token. However, since the file has been linked on the server, the user who accessed the linked file via the cache will not be able to modify, rename or remove it in any way.

On AIX 4.2, you can prevent the second and third problems by using the noac option when you are remotely mounting your Data Links File System via NFS:

   mount -o noac yourserver:/datalink /datalink

This workaround does not appear to work on AIX 4.3.x. To ensure the directory name lookup cache in NFS is refreshed on these systems after linking files, you might want to perform an operation that updates the directory modification timestamp for the parent directory of the linked files. For example, you might use the touch command to create a zero-length file in the parent directory immediately after linking files.