5 ways to track Database Schema changes – Part 4 – DDL Trigger

This is the fourth post from my short 5 part series in which I demonstrate you 5 different ways to track database schema changes. Thanks to this, you always can easily answer questions about what has changed, who changed it and when. Today, I describe how to use DDL Trigger for this purpose.

Here you can find my previous posts from this series:

DDL Triggers

The fourth option is a DDL Trigger. These kinds of triggers are executed in response to Data Definition Language (DDL) events. They can be created in the database or server scope. Database-scoped DDL triggers are stored as objects in the database in which they are created. Server-scoped DDL triggers are stored in the master database. They can be created to be fired in response to a single particular event or the event from a predefined event group.

In our case, we are interested in capturing all events from the DDL_DATABASE_LEVEL_EVENTS group.

To get information about the event that fired our DDL trigger, we use the EVENTDATA()function. It returns an XML value that contains details about the event that triggered the execution of the trigger.

Create DDL Trigger

To log objects’ changes we first have to create a table to which we will save captured events. Below code snippet shows the simplest possible table structure that can be used for this purpose.

CREATE TABLE [dbo].[DatabaseLogs](
    [Id] [int] IDENTITY(1,1) NOT NULL,
    [DateTime] [datetime] NOT NULL 
    CONSTRAINT DF_DatabaseLogs_DateTime DEFAULT (GETDATE()),
    [EventData] [xml] NULL,
    CONSTRAINT [PK_DatabaseLogs] PRIMARY KEY CLUSTERED ( [Id] ASC ) 
)
GO

CREATE NONCLUSTERED INDEX nix_DatabaseLogs ON [dbo].[DatabaseLogs] ([DateTime] ASC) INCLUDE ([Id]);
GO

The trigger can be created using this query.

CREATE TRIGGER [tr_DatabaseLogs]
ON DATABASE 
FOR DDL_DATABASE_LEVEL_EVENTS 
AS
BEGIN
    SET NOCOUNT ON;

    IF OBJECT_ID('dbo.DatabaseLogs') IS NOT NULL
    BEGIN

        BEGIN TRY
            DECLARE @Eventdata XML;
            SET @Eventdata = EVENTDATA();

            INSERT dbo.DatabaseLogs (
              [DateTime]
            , [EventData]
            )
            VALUES (
              GETUTCDATE()
            , @Eventdata
            );
        END TRY

        BEGIN CATCH
            SET @Eventdata= NULL;
        END CATCH
    END
END
GO

Pay attention to the additional checks that are implemented in case if the table is dropped or if the insert statement fails. It is critical to keep such DDL trigger transparent to the users and applications to not impact their work if something goes wrong.

DDL Triggers - SSMS

Viewing logged events

Execute this simple SELECT statement to view the log of captured object modifications.

SELECT * FROM dbo.DatabaseLogs ORDER BY [DateTime];

DDL Triggers - ResultHere, you have an example of one of the inserted XMLs.

<EVENT_INSTANCE>
    <EventType>CREATE_PROCEDURE</EventType>
    <PostTime>2018-11-17T17:52:51.700</PostTime>
    <SPID>54</SPID>
    <ServerName>MAREK-PC\SS2017</ServerName>
    <LoginName>Marek-PC\Marek</LoginName>
    <UserName>dbo</UserName>
    <DatabaseName>TrackMyChanges</DatabaseName>
    <SchemaName>dbo</SchemaName>
    <ObjectName>usp_NewProc</ObjectName>
    <ObjectType>PROCEDURE</ObjectType>
    <TSQLCommand>
        <SetOptions ANSI_NULLS="ON" ANSI_NULL_DEFAULT="ON" ANSI_PADDING="ON" QUOTED_IDENTIFIER="ON" ENCRYPTED="FALSE" />
        <CommandText>CREATE PROCEDURE dbo.usp_NewProc
AS
BEGIN
SELECT 'Version 1';
END
        </CommandText>
    </TSQLCommand>
</EVENT_INSTANCE>

Of course, it is possible to extract this detailed information in the trigger itself and insert them into additional columns in the logging table.

Extended DDL Trigger

As a first step, we have to extend our logging table.

CREATE TABLE [dbo].[DatabaseLogs](
    [Id] [int] IDENTITY(1,1) NOT NULL,
    [DateTime] [datetime] NOT NULL CONSTRAINT DF_DatabaseLogs_DateTime DEFAULT (GETDATE()),
    [ServerName] [nvarchar](128) NULL,
    [ServiceName] [nvarchar](128) NULL,
    [SPID] [int] NULL,
    [SourceHostName] [nvarchar](128) NULL,
    [LoginName] [nvarchar](128) NULL,
    [UserName] [nvarchar](128) NULL,
    [SchemaName] [nvarchar](128) NULL,
    [ObjectName] [nvarchar](128) NULL,
    [TargetObjectName] [nvarchar](128) NULL,
    [EventType] [nvarchar](128) NULL,
    [ObjectType] [nvarchar](128) NULL,
    [TargetObjectType] [nvarchar](128) NULL,
    [EventData] [xml] NULL,
    CONSTRAINT [PK_DatabaseLogs] PRIMARY KEY CLUSTERED ( [Id] ASC ) 
)
GO

CREATE NONCLUSTERED INDEX nix_DatabaseLogs ON [dbo].[DatabaseLogs] ([DateTime] ASC)  INCLUDE ([Id]);
GO

Such table structure should be sufficient to meet most needs. As the next step, we must implement XML parsing logic in our DDL Trigger. To do this, we use SQL Server XQuery methods.

CREATE TRIGGER [tr_DatabaseLogs]
ON DATABASE 
FOR DDL_DATABASE_LEVEL_EVENTS 
AS
BEGIN
    SET NOCOUNT ON;

    IF OBJECT_ID('dbo.DatabaseLogs') IS NOT NULL
    BEGIN
        BEGIN TRY
            DECLARE @Eventdata XML;
            SET @Eventdata = EVENTDATA();

            INSERT dbo.DatabaseLogs (
              [DateTime]
            , [ServerName]
            , [ServiceName]
            , [SPID]
            , [SourceHostName]
            , [LoginName]
            , [UserName]
            , [SchemaName]
            , [ObjectName]
            , [TargetObjectName]
            , [EventType]
            , [ObjectType]
            , [TargetObjectType]
            , [EventData]
            )
            VALUES (
              GETUTCDATE()
            , @@SERVERNAME
            , @@SERVICENAME
            , @Eventdata.value('(/EVENT_INSTANCE/SPID)[1]', 'int')
            , HOST_NAME()
            , @Eventdata.value('(/EVENT_INSTANCE/LoginName)[1]', 'nvarchar(128)')
            , @Eventdata.value('(/EVENT_INSTANCE/UserName)[1]', 'nvarchar(128)')
            , @Eventdata.value('(/EVENT_INSTANCE/SchemaName)[1]', 'nvarchar(128)')
            , @Eventdata.value('(/EVENT_INSTANCE/ObjectName)[1]', 'nvarchar(128)')
            , @Eventdata.value('(/EVENT_INSTANCE/TargetObjectName)[1]', 'nvarchar(128)')
            , @Eventdata.value('(/EVENT_INSTANCE/EventType)[1]', 'nvarchar(128)')
            , @Eventdata.value('(/EVENT_INSTANCE/ObjectType)[1]', 'nvarchar(128)')
            , @Eventdata.value('(/EVENT_INSTANCE/TargetObjectType)[1]', 'nvarchar(128)')
            , @Eventdata
            );
        END TRY

        BEGIN CATCH
            SET @Eventdata= NULL;
        END CATCH
    END
END
GO

Thanks to this solution we can easily filter logged events without the need to write complicated ad-hoc queries using XQuery.

What was captured by DDL Trigger?

DDL Triggers capture very similar pieces of information to the Extended Events Sessions. We know what object was changed, when it was done, and by whom. We also have access to the SQL query that was executed.

Data retention

In this case, there is no default mechanism that clean up old data. If you need one, you have to implement it by yourself. Otherwise, the logging table will contain all events since DDL Trigger has been created. That, of course, has some advantages and disadvantages.

DDL Triggers summary
Advantages:

  • Contains a lot of details
  • Info WHAT exactly was changed
  • Access to the executed SQL statement
  • Info WHEN object was changed
  • Info by WHO object was changed
  • Data logged to the user table
  • Easy to set up
  • Possibility to set additional filters
  • Easy viewing
Disadvantages:

  • No default data retention options
  • No access to the old object definition

In the next part, I will demonstrate you how to use SQL Server Audit to capture database schema changes.

-Marek

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5 ways to track Database Schema changes – Part 3 – Extended Events Session

Last week I published the second post from my short 5 part series in which I demonstrate you 5 different ways to track database schema changes. Thanks to this, you always can easily answer questions about what has changed, who changed it and when. Today’s post describes how to use Extended Events Session for this purpose.

You can find my previous post here:

Extended Event Session

The third option is the Extended Events Session. This functionality has been introduced in SQL Server 2008. It provides very lightweight monitoring and event tracking system that can be very helpful in performance troubleshooting and (in our case) changes monitoring.

Microsoft announced it as a successor of SQL Trace (that has been marked as deprecated in SQL Server 2012). That means SQL Trace can be removed in one of the future versions. However, SQL Trace and SQL Server Profiler are still very popular and widely used, so I really doubt that will happen anytime soon.

In the beginning, Extended Events didn’t gain too much popularity because it was tough to use them. Now, with the help of SSMS, it’s much more comfortable.

To test this solution we have to create an Extended Events Session that captures object modification events. In our case these are:

  • object_created
  • object_altered
  • object_deleted
Creating an Extended Events Session

You can create such session in two ways. Using T-SQL or using a Wizard in SQL Server Management Studio. I find the latter much more comfortable.

Create a Session using Wizard

To create a new Session, in Object Explorer expand Instance -> Management -> Extended Events. Right Click on Sessions and choose New Session Wizard.

Extended Events Wizard - Start Wizard

On the “Set Session Properties” page provide a name for your session and decide if this session should start at server startup. Then, click the Next button.

Extended Events Wizard - Session Properties

On the next page, you can decide whether you want to use a predefined template or not. In our case, there is no template that we can use to track object schema changes. Choose “Do not use template” option and click “Next”.

Extended Events Wizard - Template

On the “Select Events To Capture” page, select object_altered, object_created, and object_deleted events.

Extended Events Wizard - Events To Capture

It should look like this:

Extended Events Wizard - Events To Capture 2On the “Capture Global Fields” page, you can decide what data you want to collect. My recommendation is to select the following ones:

  • client_app_name
  • client_hostname
  • database_id
  • database_name
  • server_principal_name
  • session_id
  • sql_text

This gives you an overview of what really happened. You know who performed a change, from which machine, and from which application. Most importantly, you also know what SQL statement was executed. When you set this then click “Next”.

Extended Events Wizard - Capture Global Fields

On the “Set Session Event Filters” page, you can add additional filters. That enables you, for example, to capture events just for one database instead of for all databases on your instance. Then click “Next”.

Extended Events Wizard - Session Event Filters

On the “Specify Session Data Storage” page, you need to decide if you want to log data to file(s) (event_file target) or maybe keep them in memory (ring_buffer target). For real-life usage, you should choose files. Here, for the demo purpose, I use ring_buffer.

Extended Events Wizard - Data Storage

When the session is already created, you can start it immediately and also can watch live data on the screen as events are captured.

Extended Events Wizard - Session Created

Create a Session using T-SQL

The same session can be created using this script.

CREATE EVENT SESSION [CaptureObjectModifications] ON SERVER 
ADD EVENT sqlserver.object_altered(
    ACTION(sqlserver.client_app_name, sqlserver.client_hostname, sqlserver.database_id, sqlserver.database_name, sqlserver.server_principal_name, sqlserver.session_id, sqlserver.sql_text)),
ADD EVENT sqlserver.object_created(
    ACTION(sqlserver.client_app_name, sqlserver.client_hostname, sqlserver.database_id, sqlserver.database_name, sqlserver.server_principal_name, sqlserver.session_id, sqlserver.sql_text)),
ADD EVENT sqlserver.object_deleted(
    ACTION(sqlserver.client_app_name, sqlserver.client_hostname, sqlserver.database_id, sqlserver.database_name, sqlserver.server_principal_name, sqlserver.session_id, sqlserver.sql_text))
ADD TARGET package0.ring_buffer(SET max_events_limit=0,max_memory=102400)
GO
Viewing events captured by the Extended Events Session

When the session is already created and started. It captures all object modifications. To see changes live, start the Wach Live Data view in SSMS.

Extended Events - Start Watch Live Data

You can right click on the column names to add additional columns to this view.

Extended Events - Watch Live Data - Add Columns

Now, let’s test it by executing the whole test case from the beginning of the article. Captured events are automatically displayed in the window.

Extended Events - Watch Live Data

To review historical data from the ring_buffer target, you need to use the T-SQL query. When you log to files you have the possibility to review their content in SSMS with View Target Data option. Use this query to select captured events for our session.

;WITH raw_data(t) AS
(
    SELECT CONVERT(XML, target_data)
    FROM sys.dm_xe_sessions AS s
    INNER JOIN sys.dm_xe_session_targets AS st
    ON s.[address] = st.event_session_address
    WHERE s.name = 'CaptureObjectModifications'
    AND st.target_name = 'ring_buffer'
),
xml_data (ed) AS
(
    SELECT e.query('.') 
    FROM raw_data 
    CROSS APPLY t.nodes('RingBufferTarget/event') AS x(e)
)
SELECT * --FROM xml_data;
FROM
(
  SELECT
    [timestamp]       = ed.value('(event/@timestamp)[1]', 'datetime'),
    [database_id]     = ed.value('(event/data[@name="database_id"]/value)[1]', 'int'),
    [database_name]   = ed.value('(event/action[@name="database_name"]/value)[1]', 'nvarchar(128)'),
    [object_type]     = ed.value('(event/data[@name="object_type"]/text)[1]', 'nvarchar(128)'),
    [object_id]       = ed.value('(event/data[@name="object_id"]/value)[1]', 'int'),
    [object_name]     = ed.value('(event/data[@name="object_name"]/value)[1]', 'nvarchar(128)'),
    [session_id]      = ed.value('(event/action[@name="session_id"]/value)[1]', 'int'),
    [login]           = ed.value('(event/action[@name="server_principal_name"]/value)[1]', 'nvarchar(128)'),
    [client_hostname] = ed.value('(event/action[@name="client_hostname"]/value)[1]', 'nvarchar(128)'),
    [client_app_name] = ed.value('(event/action[@name="client_app_name"]/value)[1]', 'nvarchar(128)'),
    [sql_text]        = ed.value('(event/action[@name="sql_text"]/value)[1]', 'nvarchar(max)'),
    [phase]           = ed.value('(event/data[@name="ddl_phase"]/text)[1]',    'nvarchar(128)')
  FROM xml_data
) AS x
WHERE phase = 'Commit'
ORDER BY [timestamp];

Extended Events - TSQL

What was captured by Extended Events Session?

In terms of what was captured, the Extended Event Session looks very well. It has a variety of configuration options that allow you to customize the logged details. Viewing the data collected by session, we know what was changed, when it was changed and by whom. We also have a SQL statement that was executed to perform this change.

Data retention

The Extended Events Session has many retention options for both targets. For files, we can specify the maximum files size. For the ring buffer, we can specify maximum events count and memory size. That gives users a lot of flexibility.

Extended Events summary
Advantages:

  • Contains a lot of details
  • Info WHAT exactly was changed
  • Access to the executed SQL statement
  • Info WHEN object was changed
  • Info by WHO object was changed
  • Plenty of retention options
  • Possibility to save data to memory or files
  • Easy to set up
  • Possibility to set additional filters
Disadvantages:

  • Difficult processing of captured events (T-SQL and XQuery)
  • No access to the old object definition

In the next part, I will demonstrate you how to use DDL Triggers to capture database schema changes.

-Marek

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