Naveen - He provided figures, and they are on the handout that is somewhere in my office. Maybe I'll run across it someday, or even better, maybe he'll publish his results. Here are a few more details that I posted to this list earlier. Kevin Loney (author of Oracle DBA Handbook) has performed index performance tests and presented a paper at our Twin Cities Oracle User's Group (http://www.tcoug.org). I don't know if his paper is on that site or if Kevin has posted it somewhere or if he will included his findings in a future book. His results (from memory) was that there weren't any big surprises. Say it takes 1 hour to load a table with no indexes on it. If you put 1 index on that table, load time will increase about 20% to maybe 1hr 12 minutes (depending on how many columns are indexed, etc.). If we add a second index, load time will again increase, but by a smaller amount than for the first, maybe to 1 hr. 23 minutes. And so it goes. By the time we reach 20 indexes, adding a 21st index may add only 3 or 4 minutes to our load time. There didn't seem to be any point where adding one more index would throw load times into a black hole and double load times or something like that. Kevin also tested whether the size of the index mattered. There were points where say, the 100,000th row caused index performance to suddenly drop, probably due to factors like adding a newer blevel. However it was almost impossible to predict this point ahead of time. My conclusions: - Dropping indexes speeds inserts. - If you have a single index on a table, adding a second index is costly. - If the table already has 20 indexes, one more isn't going to have a noticeable effect.
Dennis Williams DBA, 40%OCP Lifetouch, Inc. [EMAIL PROTECTED] -----Original Message----- Sent: Saturday, October 26, 2002 3:43 AM To: Multiple recipients of list ORACLE-L Dennis, Did he publish any figures? I mean, it seems common-sense that adding the first index will hurt but adding 11th index to a table won't hurt that much. As stephane pointed out, cost of an index is 2.5 times more than the cost of insert in a non-indexed table. So assuming cost is 1, than cost with 1 index will be 3.5 as 250% increase. Cost with 5 indexes should be 13.5 and cost with 6 indexes will be 16 less than twenty percent increase. Since the addition cost is constant for every index added, the percentage increase in cost (and also maybe time) will be lower and lower. Am I right or missing something? Regards Naveen -----Original Message----- Sent: Friday, October 25, 2002 11:45 PM To: Multiple recipients of list ORACLE-L Stephane You mentioned "each additional index costs about 2.5 times the cost of inserting into a non-indexed table". I just wanted to point out that Kevin Loney has done some performance tests involving the number of indexes. I don't know if he has published these anywhere. In a nutshell, the results were that a single index really hurts insert performance, and each additional index increases the hurt, but by a decreasing amount. The conclusions were: - If you can drop all indexes, that will really help inserts. - If you have one index, adding a second index will really hurt, but not as bad. - If the table already has 15 indexes, adding one more index probably won't be noticed. Dennis Williams DBA, 40%OCP Lifetouch, Inc. [EMAIL PROTECTED] -----Original Message----- Sent: Friday, October 25, 2002 8:04 AM To: Multiple recipients of list ORACLE-L Rahul wrote: > > List, > i have two heavily inserted tables, the structures are same. > currently these tables reside on separate disks, can i increase the > performance > of inserts if i create these tables in a cluster ? as a cluster would force > the rows of both the tables > to be physically close on the disk ! > > regards > -rahul > > Ora 7.3 on AIX > You would also increase contention ... I'd rather try to augment the number of free lists, and, if you are lucky enough not to access your indexes in RANGE SCAN mode, to create them as REVERSE. Beware of indexes, by the way, each additional index costs about 2.5 times the cost of inserting into a non-indexed table (in terms of logical blocks). -- Regards, Stephane Faroult Oriole Software -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Stephane Faroult INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). 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You may also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: DENNIS WILLIAMS INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
