Online 7.x performance on a single CPU machine

Over the past couple of years, I have noticed the following effect on both HP/UX and AIX single CPU platforms when running Informix Online 7.x: When running just OLTP type applications, it is possible to tune the engine to perform quite well. At least equal to, and in some cases better than 5.x on the same platform. (The improvements usually come from better query plans when the appropriate update statistics statements are used.) When a single user executes a "large" query, 7.x again often outperforms 5.x. However, when a "large" query is running under 7.x, OLTP users experience extremely poor performance -- worse than when the same query was running under 5.x. As near as I can tell, this seems to be due to the multi-threaded acrchitecture of 7.x. It seems that a CPU virtual processor "cooperatively" multi-tasks its threads. That is a thread must periodically yield in order to allow another thread to run. When a big query is running, the thread running that query does not yield often enough to allow the CPU VP to respond rapidly to small OLTP type queries. Even doing a simple "fetch next" on a cursor which is already open results in an unusual delay while the thread doing the fetch waits for the "big query" thread to yield. Under 5.x this did not occur because each user session was a different UNIX process, and UNIX pre-emptively multi-tasks its processes. Thus under 5.x even a "big" query could be pre-empted at any time for a context switch to another process. On a 4+ CPU machine, 7.x does not usually have this problem because each CPU VP is a separate UNIX process and can thus be pre-empted, even if it is running a "big" query. Run enough big queries, however, and I'm sure the same thing would start to happen. While the merits of multi-threading can be argued back and forth, it is clear that for the above scenario it does not work out so well. On a single CPU machine, even a single "big" query sends OLTP performance down the tubes. Has anyone found a reasonable work-around to this problem? I have tried experimenting by setting the PDQPRIORITY of the "big" query to various numbers above 2 in order to have them treated as DSS queries. (Based on the implication in the manuals that PDQPRIORITY 0 queries -- non DSS queries -- are give a higher priority by the engine than DSS queries.) This seems to sometimes help a little bit, in that the OLTP queries don't suffer quite as much, but the improvement is still not enough to make the performance acceptable in most situations. Are there any other parameters that might help? In general, it would be nice if Informix provided some means of setting thread priorities other than PDQPRIORITY, or at least forced "big" queries to yield more often depending on PDQPRIORITY or some other setting. -- Irwin Goldstein Objective Software Systems, Inc. http://www.objectsoft.com