PC_POOLSIZE?

IDS 12.10.FC12 Solaris 10 1/13 How does PC_POOLSIZE get changed? In our ONCONFIG file, the PC_POOLSIZE parameter is entered as: PC_POOLSIZE 127 The first few lines of 'onstat -g prc' are as follows: informix@ifmx-prod-anc>onstat -g prc|more IBM Informix Dynamic Server Version 12.10.FC12 -- On-Line -- Up 22 days 08:15:40 -- 19693568 Kbytes UDR Cache: Number of lists : 31 PC_POOLSIZE : 566 How did PC_POOLSIZE get to be 566? I do have AUTO_TUNE set to 1, but I don't seem to see anything in the documentation for "AUTO_TUNE" that would lead me to believe that PC_POOLSIZE is one of the parameters that AUTO_TUNE adjusts dynmaically. Maybe I am just not understanding the documentation. I welcome an explanation. Thank you. DG

Original post: IDS 12.10.FC12 Solaris 10 1/13 How does PC_POOLSIZE get changed? In our ONCONFIG file, the PC_POOLSIZE parameter is entered as: PC_POOLSIZE 127 The first few lines of 'onstat -g prc' are as follows: informix@ifmx-prod-anc>onstat -g prc|more IBM Informix Dynamic Server Version 12.10.FC12 -- On-Line -- Up 22 days 08:15:40 -- 19693568 Kbytes UDR Cache: Number of lists : 31 PC_POOLSIZE : 566 How did PC_POOLSIZE get to be 566? I do have AUTO_TUNE set to 1, but I don't seem to see anything in the documentation for "AUTO_TUNE" that would lead me to believe that PC_POOLSIZE is one of the parameters that AUTO_TUNE adjusts dynmaically. Maybe I am just not understanding the documentation. I welcome an explanation. Thank you. DG Response: So a couple thoughts. First is would there be any chance you have PC_POOLSIZE in your onconfig more then 1 time? If that is the case, it would take the last entry it found for the value. Second, it does appear that you could use onmode -wm to modify this parameter dynamically as long as you are increasing the size. You should be able to run onstat -g cfg full (will probably want to redirect the value to a file), then search the file for PC_POOLSIZE and it will show default, current, and onconfig values. So I would guess if the first idea isn't happening, then onconfig setting will be 127 and current I believe would show 566. That could happen via onmode -wm (so it was ran and only changed memory, not file). Lastly, a quick look at code does seem to show that for certain conditions while processing a cache misses, the server would increase the size of the cache by 10% of it's current size (whether this happens or does not appear to be controlled by AUTO_TUNE, it looks like the server has been coded to just increase the size to reduce certain types of cache misses...so not every cache miss would trigger the increase in size). I'm not 100% certain of this because I believe the server has 2 different implementations of caches and a quick look it wasn't easy to tell if the procedure cache is implemented in this manner or not. I would infer that it is using this method of caching if idea's 1 and 2 are not true, as then that would explain the increase in the cache size. A quick look at this code also didn't seem to show a way to limit growth in this case. Also, in this automatic growth case, the onstat -g cfg full would also show the current value as 566, so from just that output it wouldn't be possible to distinguish option 2 from option 3, as option 3 also ends up setting the "current" size displayed in the onstat -g cfg full. Jacques Renaut HCL Informix Advanced Support

Thank you, Jacques, for your thorough and helpful response. First, I checked, and PC_POOLSIZE is defined only once in ONCONFIG. Second, I have not changed PC_POOLSIZE via 'onmode -wm'. Third, 'onstat -g cfg full' shows default: 126; onconfig: 127; and current: 566. I conclude that Informix has made adjustments automatically. It would be helpful if that were in the documentation. (Maybe it is, but I just didn't see it.) But, I would also offer the thought that, if Informix automatically adjusts the PC_POOLSIZE, maybe it should also adjust the PC_HASHSIZE. In this instance, although PC_POOLSIZE has increased to 566, PC_HASHSIZE remains at 31. There is a very high disparity in the "hits" column-- from 2 to about 100,000,000. I think I should manually increase PC_HASHSIZE. I'll try 127, and see if that that "spreads out" the distribution a little more. DG

Oops. Informix won't let me do this. That is, one cannot use 'onmode -wm' or 'onmode -wf' to change the value of PC_HASHSIZE. (At least the documentation would seem not to offer this as an option-- see https://www.ibm.com/support/knowledgecenter/en/SSGU8G_12.1.0/com.ibm.adref.doc/i ds_adr_0131.htm ) I'll have to wait for our next maintenance period, as this is a production instance. DG

Original post: Oops. Informix won't let me do this. That is, one cannot use 'onmode -wm' or 'onmode -wf' to change the value of PC_HASHSIZE. (At least the documentation would seem not to offer this as an option-- see https://www.ibm.com/support/knowledgecenter/en/SSGU8G_12.1.0/com.ibm.adref.doc/i ds_adr_0131.htm ) I'll have to wait for our next maintenance period, as this is a production instance. DG Response: Yeah, going with your previous post as well, the server doesn't allow the value of PC_HASHSIZE to be changed on the fly, as it's used as part of hashing into the cache. If you allowed that to change, you would potentially be moving the location of lots (?) of items in the cache. So the server would probably have to just rebuild the entire cache, which I'm guessing the complexities of doing that while online was not worth the risk so it's not allowed. Jacques Renaut HCL Informix Advanced Support