If in oracle 9i release 2, you should be at patchset 9. This information is incorporated into the data dictionary by the smon process at a preset interval every 3 hours in oracle 8. Managing automatic optimizer statistics collection or gathering statistics manually. The source database must be at least in the following patchset levels. Managing optimizer statistics in an oracle database 11g. However, recently since oracle 10g oracle has provided some methods internal to the database that help in gathering object statistics automatically. Some queries that ran for 50 seconds are not finishing. Oracle isv migration center upgrade to oracle database 11g. Upgrade from oracle 9i to 11g database upgrade from 9i to 11g the following is a real scenario for upgrading a 9. Oracle database performance tuning guide for more information about managing optimizer statistics.
Oracle can gather some statistics automatically while creating or rebuilding a btree or bitmap index. The statistics can reside in the dictionary or in a table created in the users schema for this purpose. A pdb has a dictionary and the auto gather stats job will refresh the dict stats as well. Fixed objects statistics and why they are important oracle.
This parameter is ignored if you are running a database prior to oracle 9i release 2 9. Download current version and spool the output utlu112i. Customer was not happy that dictionary statistics was taking long time after database upgrade. Gathering statistics for all fixed objects in the data dictionary. Gathering optimizer statistics for upgrading oracle database. Oracle9i supplied plsql packages and types reference. This oracle documentation was created as a support and oracle training reference for use by our dba performance tuning consulting professionals. Oracle data dictionary statistics tips expert oracle database tips by donald burleson december 8, 2015 question. Oracle gathers statistics on all database objects automatically and maintains those. Oracle provides scripts that collect optimizer statistics for dictionary objects in oracle database. If in oracle database 10g release 1, you should be at patchset 10. Oracle implicitly determines which objects need new statistics, and determines how to gather those statistics. Taking statistics and have them updated is a very important task on most oracle databases, the cbo cost based optimizer evaluates the cost of several execution paths, this cost is mainly based on physical and logical disk io, cpu use and network io, if our stats are not being taken or arent updated there is a possibility for the cbo to take a wrong decision.
When you generate statistics for a table, column, or index, if the data dictionary already contains statistics for the object, then oracle updates the existing statistics. One day, suddenly the cpu utilization on a 4 cpu sunfire 15k went up to 25% on all cpus. I do not gather system statistics or fixed object statistics in my script, as this is not recommended by oracle. Every procedure performs something like mentioned below on different tables tables are not dependent on each other on one of the table, i make the 3 indexes unusable one by one, then i alter the session using following command and then insert into that table. Ask tom how to gather stats in 11g database oracle. Table 9 default index values when statistics are missing. Ask tom oracle 9i generates statistics automatically. You must have both the analyze any dictionary, and analyze any system privilege, or the dba role. It needs to be run whenever you do big things to the dictionary loaded a schema not put data into the schema, but rather did things in the schema that affect the dictionary like creating and dropping objects you would consider gathering statistics. Dietrich flaws and pitfalls oracle database 12c 0 i really have to say thank you very much to the people out there alerting me about issues i havent seen before. Before this operation our querys run fast, but after this operation the same querys are really slow. It has 42m rows, thus, it does take a very long time to complete. When enabled, any change insert, update, delete, direct load, truncate, etc.
You can use the following oracle supplied packages. When a valid sql statement is sent to the server for the first time, oracle produces an execution plan that describes how to retrieve the necessary data. The database stores optimizer statistics in the data dictionary. If a monitored table has been modified more than 10%, then. Analyze fixed object statistics burleson oracle consulting. If you already have a wellestablished, manual statistics gathering procedure then you might prefer to use that instead. The fact is there are still some things database administrators can do to get more information into the hands of the oracle database because system statistics and fixed table statistics are not. Sep 08, 2009 oracle implicitly determines which objects need new statistics, and determines how to gather those statistics. Oracle 9i i currently have a database and i had not gather statistics for a long while. For the cdb, let auto stats deal with dictionary stats. Oracle 11g gather statistics params raadinoracle dba. To help to assure good performance, use this procedure to gather dictionary statistics after completing your upgrade. The statistics are stored in the data dictionary and can be exported from one database and.
Best practices for gathering optimizer statistics with oracle. Stats are not collected, but all the objects that will be affected when it is invoked are reported. In order to gather the stats, you need the following permissions. With solutions for toad for oracle, toad for mysql, toad for sql server, db2, sap and more. From oem, you can analyze the db in order to collect statistics and memorize these statistics in the db. However, without detailed testing, it is difficult to know which sample size to use to get accurate statistics. Dictionary statistics provide essential information to the oracle optimizer to help it find efficient sql execution plans.
User is the owner of the tables for which support requests cbo statistics. Once the workload window ends after 1,2,3 hours or whatever, stop the system statistics gathering. This procedure enables you to copy statistics from an existing sub partition to the new sub partition and will adjust statistics to account for the additional partition of data for example the number of blks, number of rows. I then delete the statistics from the db and everything return normal, the querys are fast again.
Because we dont want actual stats gathering itself to impact the system processing even more we are thinking to collect statistics quite frequent and use gather stale option. The point is we want to keep it as standard as possible for new builds, upgrades and migrations as possible, but in the meantime are flexible enough to go ondemand changes in statistics gathring like addressing special needs on skipping stats, being more frequent. In oracle 11g, there has been a restructuring of the job scheduling framework. By default oracle uses the same number of parallel server processes specified as an attribute of the table in the data dictionary degree of parallelism. Best practices for upgrading to oracle database 11g release 2. This oracle documentation was created as a support and oracle training reference. Only statistics stored in the dictionary have an impact on the costbased optimizer. Starting at least 4 weeks before the upgrade gather accurate performance statistics in oracle 8i 9i. If you clone or relocate a pdb, then of course the statistics will not require special treatment assuming they are being maintained.
Objects are considered stale when 10% of the total rows have been changed. Sets the statistics preferences of all the tables, excluding the tables owned by oracle. Use statspack export the perfstat user right before the upgrade. The optimizer statistics are stored in the data dictionary.
The cost based optimizer will decide on these, so it is useful to have better stat, so the optimizer might have better decisions. Online statistics gathering for bulk loads in oracle database 12c release 1 12. This feature will gather stats for all the index along with specified table. Second, i gather statistics on the data dictionary. Gathering dictionary statistics after upgrading oracle docs. As per oracle block samplinhg is more efficient but only in case if the data is randomly distributed across disk. When gather auto is specified, the only additional valid parameters are ownname, stattab, statid, objlist and statown. Third, i do a listing of the objects with stale stats, gather statistics on these objects for tables, table partitions, indexes. In particular, the automatic gathering of optimizer statistics. In older versions of the database this execution plan could be generated using one of two optimizers. You can monitor statistics gathering jobs using data dictionary views. Types for the minimum and maximum values and histogram endpoints include. Oracle recommends gathering dictionary statistics after upgrade.
It is suggested to gather data dictionary statistics in 9i under direct oracle support advice when performance problems are detected. Normally data dictionary statistics in 9i is not required unless performance issues are detected. Workload statistics, introduced in oracle 9i, gather single and multiblock read times. I guess the same result would be achieved when you use a analyze with full sample. See these notes on details for analyzing the fixed oracle tables. Invalidate dependent cursors this flag indicates whether cursors dependent on the table being analyzed should be invalidated or not. To improve performance of default gather stats in oracle database 11g. What type of stats to gather bonus script dba paradise.
Oct 06, 2015 upgrade from 9i to 11g the following is a real scenario for upgrading a 9. Let auto stats gather dictionary stats for you too and this is a continuous process rather than onetime operation. Gathering fixed object statistics is valuable for database performance, because these statistics help the optimizer generate good execution plans, which can. Create dictionary statistics the night before the upgrade. Speaking of upgrades, you can upgrade to oracle database 11g release 2 from the following releases only. Autofixup gather dictionary statistics after the upgrade using the command. To improve performance of default gather stats in oracle. In this post ill try to summarize all sorts of statistics in oracle, i strongly recommend reading the full article, as it contains information you may find it valuable in understanding oracle statistics. Oracle highly recommends gathering system statistics during a representative workload. When executing dictionary statistics using the command below. I was asked to analyze the database dictionary statistics that was taking long during post processing. When gather auto is specified, the only additional valid parameters are stattab, statid, objlist and statown. Starting at least 4 weeks before the upgrade gather accurate performance statistics in oracle 8i9i. Oraclebase online statistics gathering for bulk loads in.
Specify that when estimating stats oracle should use block sample or row sampling. Oracle recommends that you gather dictionary statistics both before and after upgrading the database, because data dictionary tables are modified and created during the upgrade. Just for curiosity, in which data dictionary tables, oracle stores the statistics for. In oracle 10g, gathering stale statistics for the database once a day happens by default. Oracle database dictionary statistics taking long time. Oraclebase costbased optimizer cbo and database statistics. Vi cascade this option is used in case you are gathering stats for a particular table. Hello tom i want to ask what should be the correct approach for a enterprise standard on statstics gathering for oracle dbs.
You can use time interval minutes instead of issuing startstop command manually. By running these scripts before performing the actual database. In oracle 11g, that association does not seem to be present as the query returns. Oracle toad expert blog for developers, admins and data analysts. How to backup and restore statistics oracle rac dba. Since only those tables with stale or empty stats are processed the overhead on the system is greatly reduced. Create dictionary statistics prior to the upgrade otherwise it will take significantly longer detailed scripts can be found here. The system was performing ok but i thought i should be updating stats weekly.
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