You can export and import optimizer statistics from the data dictionary to user-defined statistics tables. You can also copy statistics from one database to another database.
This section contains the following topics:
When you transport optimizer statistics between databases, you must use
DBMS_STATS to copy the statistics to and from a staging table, and tools to make the table contents accessible to the destination database.
Importing and exporting are especially useful for testing an application using production statistics. You use
DBMS_STATS.EXPORT_SCHEMA_STATS to export schema statistics from a production database to a test database so that developers can tune execution plans in a realistic environment before deploying applications.
The following figure illustrates the process using Oracle Data Pump and
Figure 17-1 Transporting Optimizer Statistics
As shown in Figure 17-1, the basic steps are as follows:
In the production database, copy the statistics from the data dictionary to a staging table using
Export the statistics from the staging table to a
.dmp file using Oracle Data Pump.
.dmp file from the production host to the test host using a transfer tool such as
In the test database, import the statistics from the
.dmp file to a staging table using Oracle Data Pump.
Copy the statistics from the staging table to the data dictionary using
This section explains how to transport schema statistics from a production database to a test database.
Prerequisites and Restrictions
When preparing to export optimizer statistics, note the following:
Before exporting statistics, you must create a table to hold the statistics. The procedure
DBMS_STATS.CREATE_STAT_TABLE creates the statistics table.
The optimizer does not use statistics stored in a user-owned table. The only statistics used by the optimizer are the statistics stored in the data dictionary. To make the optimizer use statistics in user-defined tables, import these statistics into the data dictionary using the
DBMS_STATS import procedure.
The Data Pump Export and Import utilities export and import optimizer statistics from the database along with the table. When a column has system-generated names, Original Export (
exp) does not export statistics with the data, but this restriction does not apply to Data Pump Export.
Exporting and importing statistics using
DBMS_STATS is a distinct operation from using Data Pump Export and Import.
This tutorial assumes the following:
You want to generate representative
sh schema statistics on a production database and use
DBMS_STATS to import them into a test database.
dba1 exists on both production and test databases.
You intend to create table
opt_stats to store the schema statistics.
You intend to use Oracle Data Pump to export and import table
To generate schema statistics and import them into a separate database:
On the production host, start SQL*Plus and connect to the production database as administrator
Create a table to hold the production statistics.
For example, execute the following PL/SQL program to create user statistics table
BEGIN DBMS_STATS.CREATE_STAT_TABLE ( ownname => 'dba1' , stattab => 'opt_stats' ); END; /
Gather schema statistics.
For example, manually gather schema statistics as follows:
-- generate representative workload EXEC DBMS_STATS.GATHER_SCHEMA_STATS('SH');
DBMS_STATS to export the statistics.
For example, retrieve schema statistics and store them in the
opt_stats table created previously:
BEGIN DBMS_STATS.EXPORT_SCHEMA_STATS ( ownname => 'dba1' , stattab => 'opt_stats' ); END; /
Use Oracle Data Pump to export the contents of the statistics table.
For example, run the
expdp command at the operating schema prompt:
expdp dba1 DIRECTORY=dpump_dir1 DUMPFILE=stat.dmp TABLES=opt_stats
Transfer the dump file to the test database host.
Log in to the test host, and then use Oracle Data Pump to import the contents of the statistics table.
For example, run the
impdp command at the operating schema prompt:
impdp dba1 DIRECTORY=dpump_dir1 DUMPFILE=stat.dmp TABLES=opt_stats
On the test host, start SQL*Plus and connect to the test database as administrator
DBMS_STATS to import statistics from the user statistics table and store them in the data dictionary.
The following PL/SQL program imports schema statistics from table
opt_stats into the data dictionary:
BEGIN DBMS_STATS.IMPORT_SCHEMA_STATS( ownname => 'dba1' , stattab => 'opt_stats' ); END; /
Oracle Database PL/SQL Packages and Types Reference to learn about the
Oracle Database PL/SQL Packages and Types Reference for an overview of the statistics transfer functions
Oracle Database Utilities to learn about Oracle Data Pump