SQL Server useful but less known features

  • Posted on: 2 November 2016
  • By: Michał Turecki
  1. 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]

  2. 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

  3. Checking the size of column's contents

    To check how much data the column contains:

    SELECT *, DATALENGTH([column]) AS ColumnSizeInBytes FROM table

  4. 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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