Managing temporary tablespaces effectively in Oracle 19c is critical for optimal database performance. Temporary tablespaces store transient data that persists only for the duration of a session, such as sorting operations and other intermediate processing tasks. Mismanagement or performance issues related to these tablespaces can lead to significant performance degradation, especially during large transactions or complex query operations. This blog will delve into diagnosing common temporary tablespace issues and provide strategies for resolution.
Concepts
Temporary tablespaces contain transient data that exists only for the duration of a session. They are crucial for sort operations that exceed the capacity of available memory. Within a temporary tablespace, sort operations share a single sort segment, created by the first statement that uses the tablespace for sorting and released only at shutdown. A single temporary tablespace can be shared by multiple users. You cannot explicitly create objects in a temporary tablespace, except for temporary tables.
Common Issues Involving Temporary Tablespaces
Running Out of Temporary Space (ORA-1630 and ORA-1652)
Large transactions can sometimes run out of temporary space. This issue is commonly encountered with large sort jobs, especially those involving tables with many partitions. These operations lead to heavy use of the temporary tablespaces, potentially causing performance problems.
To diagnose and resolve space management errors, the following commands can be helpful:
SELECT * FROM dba_temp_files ORDER BY tablespace_name;
SELECT * FROM v$tempfile;
ALTER TABLESPACE temp ADD TEMPFILE '/path/to/tempfile/temp03.dbf' SIZE 1000M REUSE;
ALTER DATABASE TEMPFILE '/path/to/tempfile/temp03.dbf' DROP INCLUDING DATAFILES;
Explanation:
dba_temp_filesandv$tempfileprovide detailed information about the tempfiles associated with temporary tablespaces.- Adding tempfiles can alleviate space issues by expanding the temporary tablespace.
- Dropping unnecessary tempfiles can help manage disk space and improve performance.
Dropping the Temporary Tablespace Issues
Dropping a temporary tablespace can sometimes be problematic. Here’s how to handle such issues:
DROP TABLESPACE temp INCLUDING CONTENTS AND DATAFILES;
Explanation:
- The command ensures that the tablespace is dropped along with its contents and associated datafiles, preventing orphaned files and freeing up disk space.
ORA-25153: Temporary Tablespace Is Empty Issues
When encountering ORA-25153 errors, indicating that the temporary tablespace is empty, the following commands can help:
ALTER DATABASE TEMPFILE '/path/to/tempfile/temp03.dbf' RESIZE 1000M;
Explanation:
- Resizing the tempfile can address issues related to temporary tablespace being empty or improperly configured.
Other ORA- Errors Involving the Temporary Tablespace
Other ORA- errors can be addressed with the following approach:
ALTER DATABASE TEMPFILE '/path/to/tempfile/temp03.dbf' OFFLINE;
ALTER DATABASE TEMPFILE '/path/to/tempfile/temp03.dbf' ONLINE;
Explanation:
- Taking the tempfile offline and then back online can sometimes resolve corruption or configuration issues causing ORA- errors.
High Temporary Tablespace Usage
High temporary tablespace usage can be a sign of performance issues and need resolution. Use the following queries to diagnose and manage usage:
SELECT tablespace_name, total_blocks, used_blocks, free_blocks FROM v$sort_segment;
SELECT username, sql_id, temp_bytes FROM v$sort_usage;
Explanation:
v$sort_segmentprovides insights into the blocks used within the temporary tablespaces.v$sort_usageidentifies users and SQL statements consuming significant temporary space, helping target specific queries or sessions for optimization.
Benefits of Temporary Tablespace Groups
Temporary tablespace groups offer several advantages that can significantly enhance database performance:
- Improved Resource Utilization: A single user can simultaneously use multiple temporary tablespaces in different sessions, ensuring better resource distribution.
- Database-Level Flexibility: You can specify multiple default temporary tablespaces at the database level, offering flexibility in resource allocation.
- Efficient Parallel Execution: Parallel execution servers in a parallel operation can efficiently utilize multiple temporary tablespaces, enhancing performance.
- Reduced Risk of Running Out of Sort Space: SQL queries are less likely to run out of sort space because they can now simultaneously use several temporary tablespaces for sorting.
- Reduced Contention: Using multiple temporary tablespaces reduces contention, especially in environments with high concurrent usage.
Creating a Temporary Tablespace Group
Temporary tablespace groups is a good way to provide resolution to Temp related issues. To create and manage a temporary tablespace group, use the following commands:
ALTER SESSION SET container = pdb_name; --if multitenant
CREATE TEMPORARY TABLESPACE temp_group01 TEMPFILE '/path/to/tempfile/tempgrp01.dbf' SIZE 50M TABLESPACE GROUP temp_group;
CREATE TEMPORARY TABLESPACE temp_group02 TEMPFILE '/path/to/tempfile/tempgrp02.dbf' SIZE 50M TABLESPACE GROUP temp_group;
Explanation:
- These commands create two temporary tablespaces (
temp_group01andtemp_group02) and assign them to a group (temp_group).
Viewing Temporary Tablespace Group Information
To view information about the temporary tablespace group:
SELECT group_name, tablespace_name FROM dba_tablespace_groups;
Assigning Temporary Tablespace Groups When Creating a User
To assign a temporary tablespace group to a new user:
CREATE USER new_user IDENTIFIED BY password TEMPORARY TABLESPACE temp_group;
Altering Users
To change the temporary tablespace for an existing user:
CREATE USER temp_user IDENTIFIED BY password;
ALTER USER temp_user TEMPORARY TABLESPACE temp_group;
Finding Temporary Tablespaces or Temporary Tablespace Groups Assigned to Each User
To check which temporary tablespace or temporary tablespace group is assigned to users:
SELECT username, temporary_tablespace FROM dba_users WHERE username IN ('USER1', 'USER2');
Setting a Group as the Default Temporary Tablespace for the Database
To set a temporary tablespace group as the default for the database:
ALTER DATABASE DEFAULT TEMPORARY TABLESPACE temp_group;
Finding the Name of the Current Default Temporary Tablespace on PDB Database
To find the current default temporary tablespace on a PDB database:
SELECT property_name, property_value FROM database_properties WHERE property_name = 'DEFAULT_TEMP_TABLESPACE';
Conclusion
Managing temporary tablespaces efficiently is essential for maintaining database performance in Oracle 19c. By understanding common issues, monitoring usage, and utilizing temporary tablespace groups, DBAs can ensure that their databases run smoothly and efficiently. Addressing temporary tablespace issues promptly can prevent performance bottlenecks and enhance the overall performance of the database.
Large transactions can sometimes run out of temporary space. Large sort jobs, especially those involving tables with many partitions, lead to heavy use of the temporary tablespaces, thus potentially leading to a performance issue.
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