To improve performance of default gather stats in oracle. Oracle isv migration center upgrade to oracle database 11g. Oracle provides scripts that collect optimizer statistics for dictionary objects in oracle database. Starting at least 4 weeks before the upgrade gather accurate performance statistics in oracle 8i 9i. Invalidate dependent cursors this flag indicates whether cursors dependent on the table being analyzed should be invalidated or not. For the cdb, let auto stats deal with dictionary stats. How to backup and restore statistics oracle rac dba. Oct 06, 2015 upgrade from 9i to 11g the following is a real scenario for upgrading a 9. Gathering statistics for all fixed objects in the data dictionary.
Oracle recommends gathering dictionary statistics after upgrade. Sep 08, 2009 oracle implicitly determines which objects need new statistics, and determines how to gather those 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. Third, i do a listing of the objects with stale stats, gather statistics on these objects for tables, table partitions, indexes. This oracle documentation was created as a support and oracle training reference. The optimizer statistics are stored in the data dictionary. The statistics are stored in the data dictionary and can be exported from one database and. To help to assure good performance, use this procedure to gather dictionary statistics after completing your upgrade. If in oracle 9i release 2, you should be at patchset 9. Specify that when estimating stats oracle should use block sample or row sampling. 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. By running these scripts before performing the actual database. Types for the minimum and maximum values and histogram endpoints include. Objects are considered stale when 10% of the total rows have been changed.
Create dictionary statistics prior to the upgrade otherwise it will take significantly longer detailed scripts can be found here. Speaking of upgrades, you can upgrade to oracle database 11g release 2 from the following releases only. I then delete the statistics from the db and everything return normal, the querys are fast again. 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.
Vi cascade this option is used in case you are gathering stats for a particular table. Gathering dictionary statistics after upgrading oracle docs. Oracle database performance tuning guide for more information about managing optimizer statistics. 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.
The system was performing ok but i thought i should be updating stats weekly. Oracle database dictionary statistics taking long time. 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. Oracle toad expert blog for developers, admins and data analysts. Oracle 11g gather statistics params raadinoracle dba. I guess the same result would be achieved when you use a analyze with full sample. 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. The cost based optimizer will decide on these, so it is useful to have better stat, so the optimizer might have better decisions. Oracle implicitly determines which objects need new statistics, and determines how to gather those statistics. Oracle can gather some statistics automatically while creating or rebuilding a btree or bitmap index. Oracle gathers statistics on all database objects automatically and maintains those. You can use the following oracle supplied packages. When gather auto is specified, the only additional valid parameters are stattab, statid, objlist and statown. Sets the statistics preferences of all the tables, excluding the tables owned by oracle.
Starting at least 4 weeks before the upgrade gather accurate performance statistics in oracle 8i9i. You can monitor statistics gathering jobs using data dictionary views. What type of stats to gather bonus script dba paradise. Use statspack export the perfstat user right before the upgrade. If in oracle database 10g release 1, you should be at patchset 10. Second, i gather statistics on the data dictionary. When enabled, any change insert, update, delete, direct load, truncate, etc. 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. It has 42m rows, thus, it does take a very long time to complete. Fixed objects statistics and why they are important oracle.
To improve performance of default gather stats in oracle database 11g. Best practices for upgrading to oracle database 11g release 2. Create dictionary statistics the night before the upgrade. Stats are not collected, but all the objects that will be affected when it is invoked are reported.
Best practices for gathering optimizer statistics with oracle. I was asked to analyze the database dictionary statistics that was taking long during post processing. Hello tom i want to ask what should be the correct approach for a enterprise standard on statstics gathering for oracle dbs. This feature will gather stats for all the index along with specified table. In oracle 11g, that association does not seem to be present as the query returns. Only statistics stored in the dictionary have an impact on the costbased optimizer. When executing dictionary statistics using the command below. From oem, you can analyze the db in order to collect statistics and memorize these statistics in the db. Online statistics gathering for bulk loads in oracle database 12c release 1 12. 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.
With solutions for toad for oracle, toad for mysql, toad for sql server, db2, sap and more. As per oracle block samplinhg is more efficient but only in case if the data is randomly distributed across disk. If you clone or relocate a pdb, then of course the statistics will not require special treatment assuming they are being maintained. Dictionary statistics provide essential information to the oracle optimizer to help it find efficient sql execution plans. Just for curiosity, in which data dictionary tables, oracle stores the statistics for.
If a monitored table has been modified more than 10%, then. See these notes on details for analyzing the fixed oracle tables. In oracle 11g, there has been a restructuring of the job scheduling framework. One day, suddenly the cpu utilization on a 4 cpu sunfire 15k went up to 25% on all cpus. Oracle highly recommends gathering system statistics during a representative workload. When gather auto is specified, the only additional valid parameters are ownname, stattab, statid, objlist and statown. In older versions of the database this execution plan could be generated using one of two optimizers.
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. Since only those tables with stale or empty stats are processed the overhead on the system is greatly reduced. In oracle 10g, gathering stale statistics for the database once a day happens by default. 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. Oraclebase online statistics gathering for bulk loads in. You can use time interval minutes instead of issuing startstop command manually. You can also collect and manage userdefined statistics for tables and domain indexes using this package. A pdb has a dictionary and the auto gather stats job will refresh the dict stats as well.
It is suggested to gather data dictionary statistics in 9i under direct oracle support advice when performance problems are detected. Before this operation our querys run fast, but after this operation the same querys are really slow. 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. 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. In particular, the automatic gathering of optimizer statistics. This parameter is ignored if you are running a database prior to oracle 9i release 2 9. Oracle data dictionary statistics tips expert oracle database tips by donald burleson december 8, 2015 question. Customer was not happy that dictionary statistics was taking long time after database upgrade. Ask tom how to gather stats in 11g database oracle. The database stores optimizer statistics in the data dictionary. Oracle9i supplied plsql packages and types reference.
Let auto stats gather dictionary stats for you too and this is a continuous process rather than onetime operation. Oraclebase costbased optimizer cbo and database statistics. Workload statistics, introduced in oracle 9i, gather single and multiblock read times. This information is incorporated into the data dictionary by the smon process at a preset interval every 3 hours in oracle 8. However, without detailed testing, it is difficult to know which sample size to use to get accurate statistics. The source database must be at least in the following patchset levels. You must have both the analyze any dictionary, and analyze any system privilege, or the dba role. Gathering optimizer statistics for upgrading oracle database. Managing automatic optimizer statistics collection or gathering statistics manually. I do not gather system statistics or fixed object statistics in my script, as this is not recommended by oracle. This oracle documentation was created as a support and oracle training reference for use by our dba performance tuning consulting professionals. In order to gather the stats, you need the following permissions. Autofixup gather dictionary statistics after the upgrade using the command.
User is the owner of the tables for which support requests cbo statistics. Oracle 9i i currently have a database and i had not gather statistics for a long while. Download current version and spool the output utlu112i. If you already have a wellestablished, manual statistics gathering procedure then you might prefer to use that instead. Upgrade from oracle 9i to 11g database upgrade from 9i to 11g the following is a real scenario for upgrading a 9. Managing optimizer statistics in an oracle database 11g. Gathering fixed object statistics is valuable for database performance, because these statistics help the optimizer generate good execution plans, which can.
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