Re: Checking indexes after large deletes

John, This would be a great topic for a "Chat with the lab". Thanks Kernoal John Miller wrote: > > BTSCANNER num=1,priority=low,threshold=50000,rangesize=10000 > > Here is what this paramater means: > > num= the number of btree scanner threads to start when the engine starts up > > priority= low | high > low means run the btree scanner below a normal user thread and only > give the btree scanner extra CPU cycles > high means run the btree scanner thread equal to that of a normal users > > threshold= > This is the number of times a user must encounter an index item which > has been marked for deletion, but has not been removed. Examples If you > delete 20,000 rows the delete will generate a count of 20,000 for this > index. If you then run a select that scans the index encountering 1/2 > of the index items you just deleted then this will count as 10,000 for > this index. So each index item encountered when select, inserts, > updates, delete encounter an items marked for deletion in an index but > still consuming space will count as 1 hit on this index. When this > index exceed this count the index will be compressed and rebalanced. > > rangesize= > Prior to 10.00.UC5 there was only two methods for cleaning an index, > leaf scanning (i.e. walking all leaf pages) and range scanning (i.e > walking a range of pages physically adjacent). The later is much, much > faster. Range scanning does a light scan on the index to read the > pages, avoiding saturating the buffer pool with unwanted index pages. > For small indexes they are already in the buffer pool so we will want to > user leaf scanning. This paramater determines the size cut off for > using the two different scanning methods. > > If more detail on this topic is required I would be happy to do a talk > on this at the Information on Demand Conference in October, or a Chat > with the lab talk. > > let me know. > John Miller > > > Hamilton, Jerry wrote: > > > > Yes I was interested in this too. > > > > I think a blue person came on here and said, "If you put this line in > > your onconfig, all your problems with the b-tree scanner will be > > forgotten". So I did and I forgot all about my b-tree scanner. But I > > still don't know what the heck it's doing. > > > > BTSCANNER num=1,priority=low,threshold=50000,rangesize=10000 > > > > > > > > -----Original Message----- > > From: informix-list-bounces@iiug.org > > [mailto:informix-list-bounces@iiug.org] On Behalf Of > > Darren_Jacobs@carmax.com > > Sent: Wednesday, June 07, 2006 1:58 PM > > To: TBP > > Cc: informix-list-bounces@iiug.org; informix-list@iiug.org > > Subject: Re: Checking indexes after large deletes > > > > I recall sometime back that someone was going to generate a paper on > > tuning the b-tree scanner. Anyone recall who it was? Jerry, weren't > > you interested in this too? > > > > Art, was it you by chance? > > > > peace > > > > > > > > > > > > TBP > > > > <TheBigPotato@Not > > > > Here.Co.Uk> > > To > > Sent by: informix-list@iiug.org > > > > informix-list-bou > > cc > > nces@iiug.org > > > > > > Subject > > Re: Checking indexes after large > > > > 06/07/2006 02:30 deletes > > > > PM > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Adam Tauno Williams wrote: > > > >>>I can't seem to get "onstat -g btc" to return anything in 9.21 FC4 or > > > > > >>>10.0 FC4. > >> > >>It doesn't do anything on my "10.00.UC4" box. > >> > >>There is "btree cleaner info", with "onstat -C". Is that the same > >>thing? > >> > > > > Yes ... > > > > onstat -C> > > > Use the -C option to print the file information about the B-tree scanner > > subsystem and each B-tree scanner thread. The following options are > > available with the onstat -C command: > > > > prof > > Prints the profile information for the system and each B-tree > > scanner thread hot > > Prints the hot list index key in the order to be cleaned part > > Prints all partitions with index statistics clean > > Prints information about all the partitions that were cleaned or > > need to be cleaned. > > range > > Prints the savings in pages processes by using index range scanning > > all > > Prints all onstat -C options > > _______________________________________________ > > Informix-list mailing list > > Informix-list@iiug.org > > http://www.iiug.org/mailman/listinfo/informix-list > > > > > > _______________________________________________ > > Informix-list mailing list > > Informix-list@iiug.org > > http://www.iiug.org/mailman/listinfo/informix-list