Improve this answer. Wernfried Domscheit Wernfried Domscheit What are those statistics used for? Thanks for the response. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. Email This BlogThis! Azhar Mulla June 27, at PM. Anonymous September 5, at AM. Unknown July 10, at PM. Devi October 16, at PM. Devi November 6, at PM. Hi Is there workaround without index rebuild?
I would like to recollect statistics skipping unusable indexes, but doing it on the rest drop table t; Table dropped. January 24, - am UTC. Igor, January 24, - pm UTC. Hah, but it's not so elegant ;- Anyway, what is a bit confusing is that even when I should skip these indexes and really Oracle does it in DML statements , when you start procedure to collect statistics, which is essentially select OK, a bit "strange" he doesn't.
It smells like "feature", no? January 24, - pm UTC. This setting allows all operations inserts, deletes, updates, and selects on tables with unusable indexes or index partitions. A reader, March 06, - am UTC.
March 06, - am UTC. I don't know. In DW -- it is usually a little more clear -- after you load. I've set-up a test with two identical tables with more that 1 million rows each. I then turned on table monitoring, truncated and reloaded each table. Is this the way it is supposed to work? Thank you. March 17, - am UTC. I can't find anything on Metalink. Tom, We have a v large partitioned table, around Million rows, each period we add extra partitions an analyze them.
What is the best method for gathering the global table stats, is there anyway we can get it to use the already analyzed partition stats, or will it do a scan? April 24, - am UTC. We cannot correctly determine data skew and distributions from the individual partition stats, we need to "globally" look at the table. Now, if your queries all do partition pruning down to a single partition -- you do not really need global stats Tom, what's going on here?
Fan, July 15, - pm UTC. July 15, - pm UTC. A reader, July 23, - am UTC. Hi I would like to know how estimate statistics work? If I do analyze table mytable estimate statistics sample rows and myemp has rows then how does Oracle estimate? July 23, - am UTC. Hi From your last example how does Oracle determine the total number of rows by just reading roughly rows? Does it do this: determine how many blocks are used to store these rows then get the average rows per block then multiply that to number of blocks?
If so where does it get the number of blocks? July 23, - pm UTC. July 25, - am UTC. In one of our instances, I found that sys and system have been analyzed. Would it have a negative effect on performance? July 25, - pm UTC. Thanks, -Peter. Elapsed: I thought the degree parameter is used to specify how much parallism you can use while gathering the statistics.
The job ran for more than 30 minutes. I finally had to kill it. July 26, - am UTC. You might have been lucky, you might have the most well behaved data on the planet whereby rows from 15million is representative enough to represent your data.
In most cases, it will not be. July 29, - am UTC. Hi, Tom, which is your opinion about connect as SYS to gather full statistics with the following command. August 01, - am UTC. A reader, August 01, - pm UTC. Also, analyze table t compute statistics command by default analyzes the table as well for all the columns and indexes associated with it. August 15, - pm UTC. Very helpful. Thanks much. A is the table t in your above demo with primary key defined.
Figured it out by reading fully this thread reader, August 15, - pm UTC. I should use cascade option. Tom, you are great!
August 16, - am UTC. They are running fine now on the existing tables. How about the new tables which gets added to the database. September 17, - pm UTC. Tom, great illustration. Thanks for your help. Spendid info! Thanks for the excellent tutorial We have tables where all the columns are indexed. Dillip, October 29, - pm UTC. Hi Tom, If I collect the stats using the following command, is there something missing for the CBO to generate a good execution plan?
Or what is the best command to collect the stats of a table including indexes, histograms so that the optmizer gets all the information that is needed. October 30, - am UTC. Thanks, M S Reddy. November 07, - am UTC. A reader, December 15, - pm UTC. December 16, - pm UTC. As I understand, maybe wrongly, the additional information got with skewonly helps to the optimizer. I'm right or not?. Or the question in other way. If I don't use constant values in the where clauses, required to get advantage of histograms, will I benefit of using skewonly as is explained in the article?
Thanks Tom :. December 18, - am UTC. A reader, December 18, - pm UTC. If you don't have any idea what is bind variable peeking, "In summary, bind variable peeking in Oracle 9i does not help us when we need different execution plans for different values of a bind variable.
Bind variable peeking allows the optimizer to take the value of a bind variable into account when first generating an execution plan for a SQL statement. If we know that the data distribution is heavily skewed and that future executions of the SQL statement may involve different data distributions for the bind variable value, we must still resort to using literals to get the best performance.
Dilllip, December 29, - pm UTC. December 29, - pm UTC. Dillip, December 30, - pm UTC. I am not clear how they are synonymous. Can you pls explain? Pls see the test case I have provided, I do not see any stats for non-indexed columns as method of stat collection is only indexed columns, when I collect stats using the analyze command, I see stats for all the columns for the table and then I collect histograms for the indexes columns separately.
December 30, - pm UTC. Pls see this, the two entries with end point as 0, 1 are collected by default. Let me rephrase my question then. I want to collect default histograms two values for all columns and histograms for all indexes columns 75 buckets. Tom, Thanks a lot.
Thanks again for the clarification. Dillip, January 23, - am UTC. Tom, I have one more question, if I use these two commands, will the second command again collect the table stats? January 23, - am UTC. What is the difference between for y in February 17, - am UTC. Tom, How much of a overhead a table monitoring has on a table?? Is it advisable to have table monitoring on?? Is that good approach?
March 19, - pm UTC. In what cases should I delete statistics? What is it useful for? March 31, - am UTC. I use it for testing get rid of existing, gather in a different fashion. Tom, This site is really a wonderland. Thank you so much for your hard work. A follow up on the analyze question.
I found that different analyze options can bring totally different results. At most, 'for all indexed columns' should be enought, right? Also If I run analyze using 'for all column' or using 'for all indexed columns' in one database, one important query ran really slow because the execution plan does not utilize a certain index. I looked at the query. It's actually fairly simple, one subquery then outer-join.
I don't think there is any other way I rewrite it to make it simpler. Is the analyze method the issue here? How should I go about to diagnose this type of issue?
Thank you! April 02, - am UTC. In a DW, it can be relevant. In a transactional system -- probably not. I'd need an example to look at. Jerry, April 02, - pm UTC. This is an internal application we build. Because we don't know what's data would be like, there are lots of indexes built, on all foreign keys, all id columns. Many columns can have its own index and also be part of another indexed. Also the analyze is scripted and histogram info is collect for all indexed columns. Ugly but for history and cost reason, not much can be done.
The second query runs very fast. The first one did not come back after hours. There is no data change on the static testing environment. It seems that oracle pick the wrong execution plan when given too much information. The mapping table are all id columns joining several tables together.
Statistics for database. Kashif, April 20, - am UTC. Hi Tom, You've mentioned in some earlier posts that you prefer gathering stats on a schema-by-schema basis instead of on the entire database. I've currently scheduled statistics to be gathered for the entire database for only stale objects. We have a DW here, and the load of the data into the DW happens at the beginning of the month, and the schemas I have turned monitoring on all get loaded at the same time, i. I've schedule the stats to be gathered at the middle and the end of the month.
Is this a feasible scenario for gathering stats at the database level? Any insight will be useful. Kashif P. In asking you the question, I sort of reached my own conclusion, i. April 20, - am UTC. Tom, Pasting your earlier comments on hidden columns: o for all hidden columns - gather histograms on columns you cannot see, useful if using the object relational features which incorporate tons of hidden columns in your objects.
We have high implementation of object relational features. May 13, - am UTC. Looks like I got that one wrong in researching that further. A reader, May 13, - am UTC. So my guess is it speeds up the refresh process. Right Tom? One more thing just to know that I am doing right: Everyday in the morning the tables get loaded fresh through a batch job.
Is this a suggested way or are there any other tips to do this. Also will the users get a performance degradation while the stats are being refreshed? I o analyze tables first time after creation o alter them to be monitoring o gather STALE after that this is what 10g automates actually in that fashion, only objects that need to be regathered will be stale. Yes, the data changes though the no of records dont' jump up much. I would follow your steps to implement stats.
Almost all the tables are built on object types. May 13, - pm UTC. Thiru, May 13, - pm UTC. Thanks for the input. One last thing: a.
How to determine the option to be used. In that case, the first few queries would take a longer time than before. Any way to avoid this? Any performance issues while these statistics run during heavy load. I am reading your book "Effective Oracle Raaghid, May 15, - am UTC.
Is Analyze used only for statistics gathering? In nutshell, what are the usages of analyze. May 15, - pm UTC.
Please see the admin and performance guides. A reader, May 31, - pm UTC. May 31, - pm UTC. If you omit this parameter, then Oracle samples rows. A reader, June 03, - pm UTC. I'm observing something similar but I will let your expertise decide which plan is "better", owing to the fact that I know very little about CBO. Is it because the tables are pretty small? Although, request table does have K rows. Thanks so much, as always.
June 03, - pm UTC. Strategy for Gather Stat. Assuming that we are in Oracle 8i which does not have auto monitor features to assist us. Based on your experience, what should be the best way to gather the statistic. How about the following strategy? What is the different between the analyze table x stimate statistics sample 5 rows and 10 rows besides the number of rows inspected to gather the statistic.
Since the system is able to get the info without going through the entire table. Is it recommended for us to gather certain percentage of row for all of our tables to shorten the gathering time. If the problem is not corrected, drop and re-create the materialized view. The following statement validates the emp table and all associated indexes:.
Because this operation can be resource intensive, you can perform a faster version of the validation by using the FAST clause. This version checks for the existence of corruptions using an optimized check algorithm, but does not report details about the corruption. The following statement performs a fast validation on the emp table and all associated indexes:. You can specify that you want to perform structure validation online while DML is occurring against the object being validated.
The following statement validates the emp table and all associated indexes online:.
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