Tempdb is a SQL Server temporary system database. Everytime SQL Server restarts, new Tempdb database is created. Whatever data was stored in the tempdb is lost. When TempDB gets recreated its data and log files reset to their last configured size. SQL Server records only enough information in the tempdb transaction log to roll back a transaction, but not to redo transactions during database recovery. This feature increases the performance of INSERT statements in tempdb. Tempdb database is always in Simple recovery mode. If you try to change it to Full Recovery mode, you will receive the following error message.
Click through for more info on how the database is special, types of issues you can run into as concurrency grows, and ways to resolve those issues.