During periods of heavy load, the SAS^® Metadata Server might become temporarily unresponsive to requests from client applications. In this situation, attempts to log in to client applications or perform any action that requires retrieving information from the SAS^® Metadata Repository might appear to hang.

This problem occurs as a result of the algorithm that the AIX operating system uses to prioritize thread locks. Update requests to the SAS Metadata Server are single-threaded, which means that once an update operation begins, all other requests are queued behind it and must wait for the write to complete before resuming. In order to coordinate these activities, the SAS Metadata Server requests an exclusive write lock from the operating system for the thread on which the update will run. SAS expects the operating system to delay granting any new shared read locks once an exclusive write lock has been obtained. However, on AIX if there are threads that currently hold a shared read lock, subsequent attempts to acquire a shared read lock request are granted, whereas the attempt to acquire an exclusive write lock waits. This means that if a long-running read request is executing when an update request is submitted, additional new read requests are allowed through while the update request is forced to wait until a window of time when there are no longer any reads executing. During this time, if multiple update requests are received by the server, they continue to queue up waiting for their exclusive write lock to be granted. Once the updates begin executing (sequentially, not in parallel), there can be a noticeable delay before the read operations resume.

Note that if the server is left undisturbed, the server request queue eventually clears and the problem resolves itself.

Click the Hot Fix tab in this note to access the hot fix for this issue.

Operating System and Release Information

Product Family	Product	System	SAS Release
			Reported	Fixed*
SAS System	SAS Metadata Server	64-bit Enabled AIX	9.1 TS1M3 SP4	9.2 TS2M2

* For software releases that are not yet generally available, the Fixed Release is the software release in which the problem is planned to be fixed.

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A fix for SAS 9.1.3 (9.1 TS1M3) for this issue is available at:

http://www.sas.com/techsup/download/hotfix/e9_sbcs_prod_list.html#031894

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A fix for SAS 9.1.3 (9.1 TS1M3) with Asian Language Support (DBCS) for this issue is available at:

http://www.sas.com/techsup/download/hotfix/e9_dbcs_prod_list.html#031894

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Due to the way the AIX operating system manages thread locks, the SAS® Metadata Server might become unresponsive for a period of time. If left alone, the server eventually catches up with queued requests and begins functioning normally again.

Type:	Problem Note
Priority:	high
Topic:	System Administration ==> Performance ==> SAS System Administration ==> Servers ==> Metadata

Date Modified:	2011-03-22 14:53:19
Date Created:	2008-04-25 13:25:12