Re: [Fwd: SeqScans Statistics 7.3_uc6]

John, please check your 7.3 release notes. There are some entries related to keyfirst scans - one of them explicitly describing the problem of seemingly increased sequential scans. Regards, Heiko "Carlson@WHSmith" wrote: > I came across this in DejaNews. I've noticed an 'increase' in > sequential scans across the board e.g. 4000 seqscans on a 10M+ row table > in the past 2 hours. Strangely enough, the users haven't noticed any > performance degradation. I'd assume they would notice that . . . > > What's the "keyfirst" feature? How does it affect the sequential scan > counter? > > TIA > > John Carlson > Informix DBA > WHSmith USA > > ------------------------------------------------------------------------ > > Subject: Re: SeqScans Statistics 7.3_uc6 > Date: Thu, 1 Apr 1999 10:08:50 -0600 > From: me@work.yet > To: carlson1@bellsouth.net > > ------------------------------------------------------------------------------ > > This message was forwarded to you from Deja News by me@work.yet. > Deja News, the discussion network, offers free web-based access to more than > 50,000 high-quality discussion forums. Come and visit us on the web at > http://www.dejanews.com/=zzz_maf/ > > ------------------------------------------------------------------------------ > > Fatbrian.com {*} is the resource for technical minds. Visit us at: > http://www1.fatbrain.com/bestsellers.asp?currsubcode=TOP&from=DNref26 > for high-tech titles, interactive training products, research reports and manuals. > > ------------------------------------------------------------------------------ > > (beginning of original message) > > Subject: Re: SeqScans Statistics 7.3_uc6 > From: Heiko Giesselmann <heikog@informix.com> > Date: 1999/03/03 > Newsgroups: comp.databases.informix > "Art S. Kagel" wrote: > > > mattb5@ozemail.com.au wrote: > > > > > > In article <7bfr9s$uoh$1@nnrp1.dejanews.com>, > > > mattb5@ozemail.com.au wrote: > > > > In article <36D5C1A6.256D@bloomberg.net>, > > > > kagel@bloomberg.net wrote: > > > > > mattb5@ozemail.com.au wrote: > > > > > > Folks, > > > > > > I have found something interesting now: > > > > > > Here are two SQL's that are practically the same, if you run these SQL's with > > > SET EXPLAIN ON, both report INDEX PATH as you would expect. However the second> > > SQL increments the sysptprof.seqscans by 1 where tabname = "msf700" > > > > > > > Question? Do you have any other evidence that a sequential scan is > > ACTUALLY happening? Perhaps the bug is that sysptprof.seqscans is being > > incorrectly updated!?!? Try zeroing stats and run the first query then > > look at onstat -D for I/O's against the chunk and onstat -p for total > > I/O and buffer activity. Then zero stats again and run the second > > query. Is there any significant difference? > > > > Art S. Kagel > > Hi, > > there is a bug related to the "keyfirst" feature that was introduced with 7.3. Due > to this bug the count of sequential scans as found in sysptprof (or as displayed in > 'onstat -p') may be higher than the number of sequential scans actually executed. > > If Explain reports an index path and at the same time seqscans is incremented I am > pretty sure that you hit this problem. It will be fixed in 7.31 (and probably some > 7.30.UCx release as well). > > Heiko > > ============= all disclaimers apply ================ > > (end of original message) > ------------------------------------------------------------------------------ > > You can view this message and the related discussion by following this link: > http://www.dejanews.com/=zzz_maf/dnquery.xp?search=thread&svcclass=dnserver&recnum=%3c36DDD8E1.E9BA04C1@informix.com%3e%231/1 > We hope to see you soon at Deja News, the discussion network. > http://www.dejanews.com/=zzz_maf/