tempdb database in Parallel Data Warehouse

tempdb is a SQL Server PDW system database that stores local temporary tables for user databases. Temporary tables are often used to improve query performance. For example, you can use a temporary table to modularize a script, and reuse computed data.

For more information about system databases, see System Databases.

Key Terms and Concepts

local temporary table
A local temporary table uses the # prefix before the table name and is a temporary table created by a local user session. Each session can only access the data in local temporary tables for its own session.

Each session can view the metadata for local temporary tables in all sessions. For example, all sessions can view the metadata for all local temporary tables with the SELECT * FROM tempdb.sys.tables query.

global temporary table
Global temporary tables, supported in SQL Server with the ## syntax, are not supported in this release of SQL Server PDW.

pdwtempdb
pdwtempdb is the database that stores local temporary tables.

PDW does not implement temporary tables by using the SQL Servertempdb database. Instead, PDW stores them in a database called pdwtempdb. This database exists on each Compute node and is invisible to the user through the PDW interfaces. In the Admin Console, on the storage page, you will see these accounted for in a PDW system database called tempdb-sql.

tempdb
tempdb is the SQL Server tempdb database. It uses minimal logging. SQL Server uses tempdb on the Compute nodes to store temporary tables that it needs in the course of performing SQL Server operations.

SQL Server PDW drops tables from tempdb when:

  • The DROP TABLE statement is executed.

  • A session is disconnected. Only temporary tables for the session are dropped.

  • The appliance is shutdown.

  • The Control node has a cluster failover.

General Remarks

SQL Server PDW performs the same operations on temporary tables and permanent tables unless explicitly stated otherwise. For example, the data in local temporary tables, just like permanent tables, is either distributed or replicated across the Compute nodes.

Limitations and Restrictions

Limitations and restrictions on the SQL Server PDWtempdb database. You cannot:

  • Create a global temporary table that begins with ##.

  • Perform a backup or restore of tempdb.

  • Modify permissions to tempdb with the GRANT, DENY, or REVOKE statements.

  • Execute DBCC SHRINKLOG for tempdbtempdb.

  • Perform DDL operations on tempdb. There are a couple exceptions to this. For details, see the following list of limitations and restrictions on local temporary tables.

Limitations and restrictions on local temporary tables. You cannot:

  • Rename a temporary table

  • Create partitions, views, or non-clustered indexes on a temporary table. ALTER INDEX can be used to rebuild a clustered index for a table created with one.

  • Modify permissions to temporary tables with the GRANT, DENY, or REVOKE statements.

  • Run database console commands on temporary tables.

  • Use the same name for two or more temporary tables within the same batch. If more than one local temporary table is used within a batch, each must have a unique name. If multiple sessions are running the same batch and creating the same local temporary table, SQL Server PDW internally appends a numeric suffix to the local temporary table name to maintain a unique name for each local temporary table.

Note

You can create and update statistics on a temporary table.ALTER INDEX can be used to rebuild a clustered index.

Permissions

Any user can create temporary objects in tempdb. Users can only access their own objects, unless they receive additional permissions. It is possible to revoke the connect permission to tempdb to prevent a user from using tempdb, but this is not recommended as some routine operations require the use of tempdb.

Related Tasks

Tasks Description
Create a table in tempdb. You can create a user temporary table with the CREATE TABLE and CREATE TABLE AS SELECT statements. For more information, see CREATE TABLE and CREATE TABLE AS SELECT.
View a list of existing tables in tempdb. SELECT * FROM tempdb.sys.tables;
View a list of existing columns in tempdb. SELECT * FROM tempdb.sys.columns;
View a list of existing objects in tempdb. SELECT * FROM tempdb.sys.objects;