SQL server performance - tempdb

When tempdb is used?

User objects:

• User-defined tables and indexes
• System tables and indexes
• Global temporary tables and indexes
• Local temporary tables and indexes
• Table variables
• Tables returned in table-valued functions

Internal Objects:

• Work tables for cursor or spool operations and temporary large object (LOB) storage.
• Work files for hash join or hash aggregate operations.
• Intermediate sort results for operations such as creating or rebuilding indexes (if SORT_IN_TEMPDB is specified), or certain GROUP BY, ORDER BY, or UNION queries.

Version Stores:

• Row versions that are generated by data modification transactions in a database that uses snapshot or read committed using row versioning isolation levels.
• Row versions that are generated by data modification transactions for features such as: online index operations, Multiple Active Result Sets (MARS), and AFTER triggers.

Temp db optimization:

1. Set the tempdb to single recovery model. Less logs.
2. Allow for tempdb files to automatically grow as required. Rule for file size increment is 2 min * the speed of IO system on which the tempdb files are located. Example: if the I/O system can initialize the database file at 50 MB/s, then auto growth increment is 50 *2 *60= 6 GB
3. Preallocate the enough large disk space for tempdb files to accommodate the typical workload in the environment.
4. Create a data file for each cpu, if the cpu is dual-core, consider it as 2 cpus.
5. Make each file the same size. This allows for optimal proportional-fill performance.
6. Put the tempdb database on disks that differ from those that are used by user databases.

Monitor the space usage:

use tempdb

go

select * from sys.dm_db_session_space_usage

select * from sys.dm_db_task_space_usage

select * from sys.dm_db_file_space_usage

http://technet.microsoft.com/en-us/library/ms345368(v=sql.105).aspx