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[back to "Optimizing server performance: Semaphores (Part 2)"]

Correlating a semaphore number with a specific process (sidebar)
Note: Part one of this article include the Analysis of a Sem.Timeouts line sidebar. This sidebar builds on that information, providing additional detail.

To view Sem.Timeouts lines, type Show Stat Sem.Timeouts at the Domino server console. If the system has experienced a semaphore timeout, a message similar to the following appears:

where 430D:58 translates to [semaphore number]:[count of occurrences]

The line indicates that two semaphore timeout types occurred. The first timeout is related to the Indexer, Name Lookup function, and occurred 58 times. The second timeout relates to a database that has large collections to be rebuilt (typically the Domino Directory) and occurred 28 times.

To associate the semaphore number with a particular area or function, see the following table. We also provide you with information about our expectations of these semaphore notifications occurring in R5. Domino developers and Lotus Customer Support provided input as to which semaphores have been the ones under the most contention (that is, they suggested the entries and prioritized the list below). We base our expectations on what we have seen to date on our R5 production servers and on Domino servers deployed by our customers. Quite a few administrators who have migrated to R5 on their servers have told us that their systems are not experiencing any semaphore timeouts.

SemaphoreDescriptionOccurs in R5?
0244 & 0245Relates to database and database queue. May appear when you have a large or very active database. Typically indicates when one task is trying to open a database, and another task is using it exclusively.Rarely
0309 & 030BRelates to view rebuilding (collection and collection queue). May appear when the database (such as Domino Directory) has very large collections to be rebuilt and the other tasks are locked out. Rarely
410FRelates to OS file system (File Descriptor Queue). May appear with many file accesses.Rarely
430DRelates to Indexer, Name Lookup function (collection and collection queue). May occur with many name lookup requests from different threads (end user or server task initiated).

Note: The Collection Group semaphores are only used by the NameLookup internal process and protect the user's list of NameLookup data structures.		Rarely
0A12 & 0A13Relates to network-level activity (buffered log package and log commit). May appear with a large burst of activity, when reporting of server’s activity occurred at rate faster than server log could update to stay in synch. Rarely
4117Relates to OS system, tracking most recently freed memory. May appear with many requests for memory from different threads. Rarely
0A0BRelates to network and session tables. May appear when there are many users connected.

Use the Show DBS command to reveal the database in question. The output reveals if a problem is from contention on the Domino Directory, which could prevent clients from authenticating in a reasonable amount of time. See the Show DBS section in the main article for more information.		This semaphore may occur in R5. It remains a semaphore for a few different situations. Contact Lotus Customer Support if you encounter this semaphore.
4113Relates to OS file system, handle table movement.Does not occur in versions R4 and later.
0255Relates to database (NSF), B-Tree access. May appear when a view is being rebuilt (whose underpinnings are a B-Tree) and there is a heavy demand for the view. Rarely in R5 (as we optimized the underlying data structures for scalability) but if it occurs, contact Lotus Customer Support.
0924Relates to server (Database Server Queue). May appear when there is much database activity concurrently for a given server. Typically seen on application serversRarely

For more information, see the following: