The degree parameter controls the number of parallel server processes that will be used to gather the statistics. Lets oracle select the degree of parallelism based on size of the object, number of cpus and initialization parameters. In your experience, how often should oracle database statistics be run. That is the fundamental concept then its just a case of making sure its fast enough, via potential options such as. Oraclebase costbased optimizer cbo and database statistics. Statistics collection enhancements in oracle database 11g. The same techniques are applicable to oracle database 11g, but note that the resource consumer groups have different names in that release. Best practices for gathering optimizer statistics with oracle. Schema stats job which will run in 8 parallel each sunday at 11.
Secondly, oracle recommends that you gather system statistics during peak load in order to give the optimizer the ability to choose the best plan based on system resource usage and throughput as well as the normal information about the database objects. How to gather optimizer statistics on 11g doc id 749227. In this blog post, we discuss one remedy to improve the efficiency of statistics gathering. In this article, we will see how oracle database 11g, 12c r2 gathers important object statistics. To provide a one stop shop for automated statistics collection operation provided in 10g and 11g. Gathering and publishing statistics independently oracle. Each new version of oracle database brings forth a new set of abbreviations for new processes.
Andrew holdsworth of oracle corporation notes that dbms. Statistics on partitioned tables burleson oracle consulting. Gathering optimizer statistics is one of lifes necessary evils even if it can take an extremely long time to complete. Oracle list a number of benefits to using it including parallel execution, long term storage of statistics and transfer of statistics between servers. Extended statistics enhancements in oracle database 11g release 2. In both cases, its a procedure call without parameters. 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. That saying translates a lot of different ways but the overall idea is that the more you know about someone or something, the more effective you can be working with that someone or something. Statistics improvements oracle database 11g release 2 11. This chapter describes how to gather database statistics for oracle database and contains the following topics.
To download the latest version of dba bundle please visit this post. For this to happen, there will need to be some time available inside the batch window after statistics for the other tables in the system have been gathered. The global statistics will be automatically updated by aggregating the new partition synopsis with the existing partitions synopsis. Best practices for statistics gathering on oracle 11g 1 run all queries against empty tables to populate column usage histograms will be gathered based on this column usage. Two scheduler windows are predefined upon installation of oracle database. Ceteris parabus, always adjust cbo statistics before adjusting optimizer parms. This type of stats is not maintained by the gather stats task. Best practices for statistics gathering on oracle 11g oraworld. Oracle database performance tuning guide for more information about managing optimizer statistics. Ask tom gather index stats ve rebuild index oracle. Finally, i want to provide an introduction to many miscellaneous features that you will come to know and love in oracle database 11g. The recommended approach to gathering statistics is to allow oracle to automatically gather the statistics.
Sep 08, 2009 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. However, without detailed testing, it is difficult to know which sample size to use to get accurate statistics. They noticed explain plan changed and they wanted to know if its linked to statistics in reality the question i had to answer was showing them that explain changed because they gathered statistics, even if they claimed they did not do anything maybe a dba did gathered statistics. I also see cases of this condition where oracle locks all sql within the library cache in anticipation of invalidations. It is available on linux, windows, solaris, hpux and aix platforms as well as the oracle cloud. How to gather optimizer statistics on 11g oracle fact. This document outline the recommended method to gather a standard set of optimizer statistics for use by the cost based optimizer under oracle 12c. Nov 26, 2011 how to restore statistics and view statistics history. Oraclebase automated database maintenance task management. It provides several procedures to gather statistics for a table, schema, or a database. Having said that, if most of your processing is done at night, having the maintenance windows opening at. This is because the costbased sql optimizer cbo relies on the quality of the statistics to choose the best execution plan for all sql statements. Managing optimizer statistics in an oracle database 11g. Install oracle database 11g and make sure the sh user is unlocked.
What type of stats to gather bonus script dba paradise. You can use the following oracle supplied packages. This article is a brief overview of the management of automated database maintenance tasks in oracle database 11g. All tables in an oracle database have this attribute set to 1 by default. Best practices for managing optimizer statistics oracle. That sounds like a long time to me, but im not a dba. Oracle database exadata cloud machine version na and later oracle cloud infrastructure database service version na and later information in this document applies to any platform. Changes in this release for oracle database sql tuning guide changes in oracle. Statistics are the primary source of information for oracle optimizer. Consider the following trace of cpu consumption over time. Types for the minimum and maximum values and histogram endpoints include. This is a performance enhancement such that statistics collection for partitioned objects does no rescan table partitions that have already been. Only statistics stored in the dictionary have an impact on the costbased optimizer. Oracle has implemented the suggested algorithms to compute the number of distinct values.
Gathering statistics oracle database xe 11gr2 jump start guide. If you already have a wellestablished, manual statistics gathering procedure then you might prefer to use that instead. But what if you are not using oracle database 11g and you cant afford to gather partition level statistic not to mention global statistics after data is loaded. The examples are intended for use on oracle database 12c and oracle database 18c. You should gather statistics on the table when the tables has a representative. When it comes to statistics within your oracle database, information is power.
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. Oracle database 19c, is the long term support release of the oracle database 12c and 18c family of products, offering customers premier and extended support through to march 2023 and march 2026 respectively. It provides data analysis and collection of operating system statistics. Shows in this scenrio there are backup of stats that exists for scott. When i analyze a table again and again,it works but it fails only in case of partition. Jun 11, 2018 how to gather optimizer statistics on 11g doc id 749227. What is the name of the default stats gathering job on 11g. Hello tom i want to ask what should be the correct approach for a enterprise standard on statstics gathering for oracle dbs. When we did the same test in 12c this did not occur.
From oracle database 12c release 1 the automatic statistics gathering job will gather statistics for fixed tables that have missing stats. Oracle enterprise manager diagnostics pack, with a graphical user interface, is the most featurerich performance tool. Evidently, it is a feature of oracle that it will temporary set a library cache lock while running a analyze on a table partition, effecting all sql that references the table. Oracle 11g gather statistics params raadinoracle dba. In addition, the statistics estimate based on the auto sampling are near to 100% accurate and much faster to gather than in previous versions, as described here. Jul 04, 2014 gather database stats procedures this procedure gathers statistics for all objects in the database. Oracle database gathers optimizer statistics on all database objects. 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. Ive tried to keep this article quite light for two of reasons. Ask tom how to gather stats in 11g database oracle. How to restore statistics and view statistics history. Since oracle 11g statistics are gathered automatically by default. Oracle to use 100 percent of the table data to collect statistics. There is no need to gather these type of stats often, usually you gather new fixed object stats after a major database or application upgrade.
To improve performance of default gather stats in oracle. Prior to prior to oracle database 11g, release 1 11. Developers and dbas get help from oracle experts on. How do i prevent oracle from locking all access to my fact table when i am analyzing a partition within a table. We are using oracle database 11g enterprise edition release 11. Our team of developers recently discovered that statistics hadnt been run our production box in over 2 12 months. The database can collect statistics for external tables in the following ways. So i suppose what you are telling is a contradicting statement. Lets oracle decide whether to collect statistics for indexes or not. 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. If a monitored table has been modified more than 10%, then these statistics are considered stale and gathered again. Im sure a lot of people will never touch these settings. Gathering dictionary statistics after upgrading oracle docs. Oracle recommends that you gather dictionary statistics both before and after upgrading the database, because data dictionary tables are modified and created.
1074 813 91 52 1211 1150 1561 420 1302 1689 982 1193 69 1270 844 110 1641 1486 702 748 1507 281 106 687 647 41 963 830 1250 1479 524 1106 934 1131 511 456 633 963 263 362 390