SQL Server useful but less known features

Michał Turecki — Wed, 02 Nov 2016 11:43:56 +0000

Checking who is connected to the database

sp_who

SELECT NULL as [Connections by Database], [host_name] AS [Client Machine], db.name AS [Database], [program_name] AS [Client Program], COUNT(*) AS [Open Connections] FROM sys.dm_exec_sessions s (nolock) LEFT JOIN sys.dm_exec_requests r (nolock) ON r.session_id = s.session_id LEFT JOIN sys.databases db (nolock) ON db.database_id = r.database_id WHERE s.session_id >= 50 -- Ignore SQL Server processes GROUP BY [host_name], db.name, [program_name] ORDER BY [Client Machine], [Database], [Client Program]
Adjusting connection pooling settings

By default pool size is 100 per database with a command timeout (effectively a connection timeout) of 15 seconds. To increase add following to the connection string:

Connection Timeout=30;Pooling='true';Max Pool Size=200
Checking the size of column's contents

To check how much data the column contains:

SELECT *, DATALENGTH([column]) AS ColumnSizeInBytes FROM table
Using SQL Server profiler

Profiler is a powerful way to debug application performance problems, to check query execution time. If you're developing any application using SQL Server as a database, running it at least once for every application release can help with pinpointing possible performance issues. Remember the rule - there should be a constant number of queries regardless of the amount of records fetched - that way application will scale better. Sometimes it's better to replace a single complex query with more simpler queries because for each result row, columns shared by joins are repeated and delivered to client for processing many times.

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Michał Turecki - databases

SQL Server useful but less known features

Checking who is connected to the database

Adjusting connection pooling settings

Checking the size of column's contents

Using SQL Server profiler