Any gotchas for STMM
in [DB2]
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From: Serge Rielau on 22 Jun 2010 11:25 On 6/22/2010 9:13 AM, Mark A wrote: > "Mark A"<noone(a)nowhere.com> wrote in message > news:hvqba4$h5f$1(a)news.eternal-september.org... >> > Recommendations for SHMALL have been all over the place, from 90% of >> > system memory, 100% of system memory, to now apparently 200% of system >> > memory. Any changes to Linux Kernel Parm recommendations should be a Hiper >> > doc APAR and not slipstreamed in the InfoCenter. > Here is where it states SHMALL should be 200% (and now enfoced that way in > 9.7.2). > "2 *<size of RAM in bytes> (setting is in 4K pages)" > http://publib.boulder.ibm.com/infocenter/db2luw/v9r7/topic/com.ibm.db2.luw.qb.server.doc/doc/c0057140.html > > Here is where it states that SHMALL should be 90%: > "...whereas the parameter SHMALL should be set to 90% of the available > memory on the database server." > http://publib.boulder.ibm.com/infocenter/db2luw/v9r7/topic/com.ibm.db2.luw.admin.perf.doc/doc/c0054689.html > > Is anyone at IBM awake these days? We are under G20 lock down, tasered into unconsciousness... The recommendation has been changed from 90% top 200%. So the 90% is outdated. I have used the Feedback button in the wrong doc to get this fixed (Hint, hint, it does NOT require an IBM employee to use this button...docs are big, mistakes happen) Cheer Serge -- Serge Rielau SQL Architect DB2 for LUW IBM Toronto Lab
From: The Boss on 22 Jun 2010 12:46 On Jun 22, 5:25 pm, Serge Rielau <srie...(a)ca.ibm.com> wrote: > On 6/22/2010 9:13 AM, Mark A wrote: > > > > > "Mark A"<no...(a)nowhere.com> wrote in message > >news:hvqba4$h5f$1(a)news.eternal-september.org... > >> > Recommendations for SHMALL have been all over the place, from 90% of > >> > system memory, 100% of system memory, to now apparently 200% of system > >> > memory. Any changes to Linux Kernel Parm recommendations should be a Hiper > >> > doc APAR and not slipstreamed in the InfoCenter. > > Here is where it states SHMALL should be 200% (and now enfoced that way in > > 9.7.2). > > "2 *<size of RAM in bytes> (setting is in 4K pages)" > >http://publib.boulder.ibm.com/infocenter/db2luw/v9r7/topic/com.ibm.db... > > > Here is where it states that SHMALL should be 90%: > > "...whereas the parameter SHMALL should be set to 90% of the available > > memory on the database server." > >http://publib.boulder.ibm.com/infocenter/db2luw/v9r7/topic/com.ibm.db... > > > Is anyone at IBM awake these days? > > We are under G20 lock down, tasered into unconsciousness... > > The recommendation has been changed from 90% top 200%. So the 90% is > outdated. > I have used the Feedback button in the wrong doc to get this fixed > (Hint, hint, it does NOT require an IBM employee to use this > button...docs are big, mistakes happen) > > Cheer > Serge What I would like to see in the docs (and "Best Practice" documents) is a rationale for these kind of recommendations. Why is 200% better than 90%? And is this valid under all circumstances, like running (many) virtualised Linux-boxes under zVM (or VMware)? As is, figures like these are just 'silver bullets' and should be handled with great caution. -- Jeroen
From: Mark A on 22 Jun 2010 15:41 "Serge Rielau" <srielau(a)ca.ibm.com> wrote in message news:88c30aFc2mU1(a)mid.individual.net... > We are under G20 lock down, tasered into unconsciousness... > > The recommendation has been changed from 90% top 200%. So the 90% is > outdated. > I have used the Feedback button in the wrong doc to get this fixed > (Hint, hint, it does NOT require an IBM employee to use this button...docs > are big, mistakes happen) > > Cheer > Serge > -- > Serge Rielau > SQL Architect DB2 for LUW > IBM Toronto Lab The following PDF docs on the IBM website still say 90% for SHMALL (I realize the PDF docs are not always up to date). The point is that the 200% recommendation in the InfoCenter docs is very recent. - DB2 9.5 Quick Beginnings for DB2 Servers - DB2 9.7 Installing DB2 Servers It also still says 90% at in this "Best Practices" document: http://www.ibm.com/developerworks/data/bestpractices/systemperformance/ The real problem is that no one seems to have known (maybe until recently) what the value of SHMALL should actually be set to on Linux, rather than the problem being any typographical errors in the doc. It may be that the 200% issue is needed to make STMM work properly on a server with a lot of DB2 instances. One IBM support person implied that to me afew months ago before it was officially recommended in the InfoCenter to use 200%. Interestingly, in 9.7.2 (but not 9.7.1 or lower) the 200% value for SHMALL Linux kernel parm is now enforced by DB2 at instance startup. I am not sure what is going to happen in 9.5.6, but the same enforcement policy would be nice, because DBA's typically cannot change these parms themselves (this is the reality of the corporate world, where the OS people with root are in a separate organization).. As far as "docs are big, mistakes happen" there is another version of that goes like this: "docs are ... big mistakes happen." I know it is sometimes hard for IBM'ers to understand, but the multi-billion dollar company I work for can be out of business in a few hours because of mistakes like these (and I don't mean discrepancies where it says 2 different things in different places, I mean the 200% recommendation is very recent). Another problem is that IBM and Red Hat don't get along that well together (on a personal level) and they are constantly pointing fingers at each other. For whatever reasons, IBM seems to be closer to SUSE. Unfortunately, DBA's in large companies rarely have control of which OS to use. This has been a problem for us in understanding how DB2 uses memory running on RHES.
From: Serge Rielau on 22 Jun 2010 16:35 Mark, As you said yourself earlier defaults change (or rather: should change). 90% may have been better in the past and the team has learned that 200% is better on average now. I don't think that 90% is wrong or right. What we are talking about here are best practices and best practices change as products change and as experience accumulates. I'm being told that not all the doc changes for the recent change from 90% to 200% have been rolled out yet and the doc team is working on it. But this is not a HIPER APAR. Your company will not go out of business because you are still, obviously successfully, using 90%. Cheers Serge -- Serge Rielau SQL Architect DB2 for LUW IBM Toronto Lab
From: Mark A on 22 Jun 2010 18:13
"Serge Rielau" <srielau(a)ca.ibm.com> wrote in message news:88cl59Fv01U1(a)mid.individual.net... > Mark, > > As you said yourself earlier defaults change (or rather: should change). > 90% may have been better in the past and the team has learned that 200% is > better on average now. > I don't think that 90% is wrong or right. > What we are talking about here are best practices and best practices > change as products change and as experience accumulates. > > I'm being told that not all the doc changes for the recent change from 90% > to 200% have been rolled out yet and the doc team is working on it. > > But this is not a HIPER APAR. Your company will not go out of business > because you are still, obviously successfully, using 90%. > > Cheers > Serge > -- > Serge Rielau > SQL Architect DB2 for LUW > IBM Toronto Lab You are wrong on several fronts. When IBM released 9.5 and 9.7, 90% was unequivocally specified as the value to use for SHMALL Linux kernel parm. I provided proof of this in the PDF manuals (the 9.7 PDF manuals are not very old). 90% has apparently been discovered to not be appropriate, and now 200% is recommended (as of just a few months ago). This had nothing to do with DB2 code changes, it had to do with problems with STMM (I was told by an IBMer that this was particularly the case if a server had a lot of DB2 instances and was doing high volume production). The recommendation is retroactive to 9.5.0. You are claiming that 90% is neither right or wrong. But the 200% setting is now enforced in future fixpacks (already in 9.7.2 and maybe in 9.5.6), so that tells me that someone in IBM think 90% is wrong, although admittedly, not every customer is going to encounter a problem if their server has only one DB2 instance and is only moderately loaded or not using STMM. The only reason we are successfully using 90% is because we turned off STMM. So either the 90% is wrong, or STMM doesn't work correctly (or some combination of the two). My company suffered serious customer relations problems with several large customers because of STMM and memory problems in general, and I don't need you to tell me what happened, since you don't know a anything about it. Sounds to me you have working been on that Oracle compatibility code for so long that you are starting to sound just like Oracle. Maybe you should apply for a job with them. |