TRANSFER Release D30 Documentation Supplement

TRANSFER D30 Documentation Supplement
TRANSFER Release D30 Documentation Supplement—118474 1-11
X400 Gateway Message Priority
Item ID Session Record Caching
The SESSION file is one of the most heavily read files of the TRANSFER delivery
system. Analysis shows that messages from a given client are frequently sent to the same
TISERV process. If the session record is kept in memory, the read of the SESSION file
is avoided, resulting in a significant performance improvement. The TISERV keeps a
cache of the most recently accessed session records. If the client uses the ALTER-SESS-
SUFFIX UOW, this caching must be turned off. A new PARAM, ALTERINGSUFFIX,
turns off caching of the session record. To instruct TISERV to do the caching, include
PARAM ALTERINGSUFFIX FALSE.
Typically, a client that does a SCAN-FOLDER UOW accesses one or more of the items
identified by the SCAN-FOLDER RSP. When the item is accessed, TISERV needs to
check to see if the user has access to the data records (or item descriptor). This check is
not necessary if the context of the SCAN-FOLDER RSP is retained.
An item ID cache is maintained, on a per-session basis, for the most recently accessed
session-id and the most recent items for that session. This cache reduces reads of the
IFOLDER and ITEMDESC file.
This item access checking is significant; the data records are blocked, so a high
percentage of the I/O on an item is security checking. In a simple test for retrieving 5
text records, the following I/Os were done:
•
One read to retrieve the session record, some of which can be avoided by caching
session records
•
One read from the IFOLDER file to determine item access security; this I/O is not
done if item ID is found in cache.
•
One read to retrieve the item descriptor record; this I/O is not done if item ID is
found in cache.
•
One read to retrieve the data from the ITEMDATA file; will not change
If the item ID is not found in the session's item ID cache, then the customary item access
checking still needs to be done. Because only a few item IDs are cached, an item ID
might not be found for a valid access, and a read of IFOLDER has to be done.
X400 Gateway Message Priority
Prior to this release, the X400-IMPORTER has set the priority of incoming messages by
using the following mapping:
This mapping is not consistent with TRANSFER values of 150, 100, and 50,
respectively.
X.400 Message Priority TRANSFER Message Priority
URGENT 125
NORMAL 75
LOW 25