Tymeac Scheduling Failures

This section discusses the common reasons why Tymeac Queues fail to schedule.

Scheduling failures (return code greater than zero) come under three categories:

Time-out,

No available Wait List, and

No available thread.

Time-out,
for Synchronous Requests, means that all components (Queues) of the request did not finish within the interval requested. Tymeac starts timing the request after scheduling all Queues. If, at the moment of expired time, the last Queue finishes, then there is no time-out. The time-out interval is unique for each request and is the user's responsibility to adjust.

For peak processing periods, such as those experienced with seasonal business, an increase in the wait time may be sufficient. However, the time-out may be due to problems relating to excessive time in application classes (i.e., waiting for strings/threads, locks, or other resources.) The On Request Statistics Class (TyStats) writes the entire Tymeac system picture to a DBMS Table or local file for review off line.

No Available Wait List
may occur for several reasons. The section, Tuning, details Tymeac's Wait List processing.

The number of entries in Wait Lists may be inadequate for which the solution is to increase the number of entries.

The number of Wait Lists, when used as an overflow mechanism, may be inadequate during peak requirements, for which the solution is to increase the number of Wait Lists.

The overflow mechanism also is true for prioritized Wait Lists. For priority 3, the request goes into Wait List 3. If Wait List 3 is full and there is no Wait List 4, the Scheduler rejects the request regardless of the status of Wait Lists 1 and 2.

An analysis of priority as well as number of Wait Lists, and number in a Wait List is necessary. Class, TyQueMaint, makes the DBMS changes to the Wait Lists.

In addition to the On Request Statistics mentioned above, several Classes are available for Wait Lists during execution.

The Wait List Display Class (TyWlData) is available for real time picture of the status of Wait Lists.

The Queue Elements Display/Alter Class (TyQueData) is available to alter the number of entries in a Queue's Wait Lists.

No Available thread
is the condition when NO Queue Thread is available for

notifying (waiting for work) or is
actively processing a request (busy) or is
about to process a request (activated or notified) or
no thread is available to reactivate (available).
The status of all threads is 'cancelled' or 'disabled'.

The section "How Threads Become Disabled" describes how threads become 'disabled'. The Queue Thread Class (TyQueThd) is available to display/alter the status of Queue threads.