How to track data lineage with SQL Server Graph Tables – Part 4 Querying the Graph Tables

In the previous article I showed you how you can populate the graph tables using the database procedures we created in an earlier post. In this article I will show you how you can query the data contained in the graph tables to quickly answer questions regarding data lineage.

Data Flow

As you may recall from the previous article, we created data to store the flow of data from two source systems in to our BI system as depicted in the illustration below.

MATCH

Starting in SQL Server 2017 the MATCH clause can be used with node and edge graph tables to traverse a path in the graph tables. Imagine a scenario where you want to know the impact of removing a field in your Staging database which you no longer believe you need. In the previous article we captured data lineage for a data flow that was coming out of JDE, one of the columns was an invoice data in Julian called RPDIVJ which is coming from the table F0411. For the purpose of this article lets assume that the business believes this date field is not useful and needs to be removed. Without this data lineage solution you would need to manually search through ETL processes to determine the impact of removing this column, a time consuming task, thankfully we have a more elegant solution.

We can query our graph tables in our DataLineage database to quickly see which processes will need to be modified. We will start by querying Staging which is the start of the data flow.

Run the following code to see which ETL process will need to be modified.

SELECT 
	df.ProcessName,
	df.CreatedDt
 FROM 
        [DataLineage].[dbo].[DataEntity] src,
        [DataLineage].[dbo].[DataFlowsTo] df,
        [DataLineage].[dbo].[DataEntity] trgt
 
WHERE MATCH(src-(df)->trgt)
	 AND src.SystemName = 'Business Intelligence System'
	 AND src.DatabaseName = 'Staging'
	 AND src.TableName = 'F0411'
	 AND src.ColumnName = 'RPDIVJ'


This should give you results like the table below.

ProcessName

CreatedDt

Load Fact Accounts Payable

2020-02-12

Load Fact Accounts Payable

2020-02-12

This tells you that the ETL process Load Fact Accounts Payable uses the field RPDIVJ in the Staging database twice. I have also included the CreatedDt filed in the query so that you know if the data is still relevant, typically the older the data the less reliable it is to make decision. If you have built your BI system correctly you should be able to compare that age of this data with the last modified date of the ETL process to see if there is a significant difference, if there is odds are you need to update the data lineage for this process.

Now let’s modify the query above to get some more meaningful insights.

SELECT 
			src.SystemName AS SourceSystem,
			src.DatabaseName AS SourceDatabase,
			src.TableName AS SourceTable,
			src.ColumnName AS SourceColumn,
			src.CreatedDt AS SourceNodeCreatedDt,
			
			df.ProcessName,
			df.CreatedDt AS ProcessCreatedDt,
			
			trgt.SystemName AS TargetSystem,
			trgt.DatabaseName AS TargetDatabase,
			trgt.TableName AS TargetTable,
			trgt.ColumnName AS TargetColumn,
			trgt.CreatedDt AS TargetNodeCreatedDt

 FROM 
	  [DataLineage].[dbo].[DataEntity] src,
          [DataLineage].[dbo].[DataFlowsTo] df,
          [DataLineage].[dbo].[DataEntity] trgt
 
WHERE MATCH(src-(df)->trgt)
	 AND src.SystemName = 'Business Intelligence System'
	 AND src.DatabaseName = 'Staging'
	 AND src.TableName = 'F0411'
	 AND src.ColumnName = 'RPDIVJ'

This query provides you with details on the source, target and the process that copies the data from source to target. When you run this query, it should provide results similar to the table below.

SourceSystem

SourceDatabase

SourceTable

SourceColumn

SourceNodeCreatedDt

ProcessName

ProcessCreatedDt

TargetSystem

TargetDatabase

TargetTable

TargetColumn

TargetNodeCreatedDt

Business Intelligence System

Staging

F0411

RPDIVJ

2020-02-12

Load Fact Accounts Payable

2020-02-12

Business Intelligence System

EDW

Fact Accounts Payable

InvoiceDate-Julian

2020-02-12

Business Intelligence System

Staging

F0411

RPDIVJ

2020-02-12

Load Fact Accounts Payable

2020-02-12

Business Intelligence System

EDW

Fact Accounts Payable

InvoiceDate-Gregorian

2020-02-12

The match clause is great however it is still difficult to understand the full impact of removing the RPDIVJ column, this only tells us about the impact to the staging load process and will not tell us down stream impacts to the EDW and the cubes which may rely on this field. What we really want to know is the shortest path across all layers of the BI system.

SHORTEST_PATH()

To get a better understanding of the end to end impact of removing this field we will use the SHORTEST_PATH option. This is a new feature only available in SQL Server 2019 or later. To use this feature, write a new query as follows.

SELECT
	CONCAT(src.SystemName,'.', src.DatabaseName, '.', src.TableName, '.', src.ColumnName) AS Source,
	COUNT(trgt.ColumnName) WITHIN GROUP (GRAPH PATH) AS [BI System Layer],
	STRING_AGG(CONCAT(trgt.SystemName, '.', trgt.DatabaseName, '.', trgt.TableName, '.', trgt.ColumnName) , ' -> ') WITHIN GROUP (GRAPH PATH) AS [Data Lineage],
	STRING_AGG(df.ProcessName , ', ') WITHIN GROUP (GRAPH PATH) AS [ETL Processes]

FROM
	[DataLineage].[dbo].[DataEntity] AS src,
	[DataLineage].[dbo].[DataFlowsTo] FOR PATH AS df,
	[DataLineage].[dbo].[DataEntity] FOR PATH AS trgt
WHERE
	MATCH (SHORTEST_PATH(src(-(df)->trgt)+))
	 AND src.SystemName = 'Finance'
	 AND src.DatabaseName = 'JDE'
	 AND src.TableName = 'F0411'
	 AND src.ColumnName = 'RPDIVJ'
ORDER BY 2 DESC

After running the query above you should get results like the table below.

Source

BI System Layer

Data Lineage

ETL Processes

Finance.JDE.F0411.RPDIVJ

3

Business Intelligence System.Staging.F0411.RPDIVJ -> Business Intelligence System.EDW.Fact Accounts Payable.InvoiceDate-Gregorian -> Business Intelligence System.SSAS Accounts Payble Model.Fact Accounts Payable.InvoiceDate

Load F0411, Load Fact Accounts Payable, Process SSAS Accounts Payble Model

Finance.JDE.F0411.RPDIVJ

2

Business Intelligence System.Staging.F0411.RPDIVJ -> Business Intelligence System.EDW.Fact Accounts Payable.InvoiceDate-Julian

Load F0411, Load Fact Accounts Payable

Finance.JDE.F0411.RPDIVJ

2

Business Intelligence System.Staging.F0411.RPDIVJ -> Business Intelligence System.EDW.Fact Accounts Payable.InvoiceDate-Gregorian

Load F0411, Load Fact Accounts Payable

Finance.JDE.F0411.RPDIVJ

1

Business Intelligence System.Staging.F0411.RPDIVJ

Load F0411

Let’s break down the results and look at the first row returned by the query.

The first column Source is the fully qualified source for the data

Finance.JDE.F0411.RPDIVJ

The second field BI System Layer tells you how many layers up the data travels, so in this case the data makes its way through all 3 layers of the BI system (Staging, EDW, SSAS).

The third field Data Lineage tells you the source to target mapping from end to end.
Business Intelligence System.Staging.F0411.RPDIVJ -> Business Intelligence System.EDW.Fact Accounts Payable.InvoiceDate-Gregorian -> Business Intelligence System.SSAS Accounts Payble Model.Fact Accounts Payable.InvoiceDate
The last field ETL Processes lets you know the names of all the ETL processes that depend on the data coming from Finance.JDE.F0411.RPDIVJ.

Load F0411, Load Fact Accounts Payable, Process SSAS Accounts Payble Model
The query is using SHORTEST_PATH, STRING_AGG and COUNT to provide meaningful information regarding data lineage on a specific field used as a source for the BI system. With this query you can quickly understand the impact of removing this field across all layers of the BI system.

Summary

By leveraging Graph tables and new querying capabilities associated with these tables you can quickly answer questions regarding data lineage and provide greater trust, understanding and ultimately adoption of the BI system.

In the next article I will cover how to visualize data in the graph tables using R.

Hopefully you have found this to be another practical post.

Until next time.

Anthony

How to track data lineage with SQL Server Graph Tables – Part 2 Create Database Procedures

This is my second post in a series which explains how to use SQL Server Graph Tables to track data lineage.

In my previous post I covered creating the node and edges tables required to store data lineage. In this post I will show you how to create database procedures in order to simplify the process of populating the graph tables. These procedures are deliberately basic so that they are easy to understand but they are also easily extensible and can serve as the starting point for a more sophisticated solution.

Overview

Before diving into the code it is always good to have a conceptual understanding of the process. The flowchart below explains the logic of these procedures.

As you can see in the diagram above, we check if the source or target is new and then based on the condition create the appropriate nodes and edges. In order to avoid duplicating code we will create a procedure for creating the nodes and the edges and then call theses sub processes from a parent process that controls the logic flow.

Create Nodes Procedure

First, we will create a procedure to populate our node table. As you recall from the previous post our node table is called [dbo].[DataEntity].

DROP PROCEDURE IF EXISTS dbo.Create_Nodes
GO

CREATE PROCEDURE dbo.Create_Nodes

    @ColumnList VARCHAR(MAX),
    @Table VARCHAR(MAX),
    @Database VARCHAR(MAX),
    @System VARCHAR(MAX)

AS
BEGIN
    SET NOCOUNT ON;
    DECLARE @NodeIDs TABLE (ID NVARCHAR(1000));

    --Insert data ino Node table and keep Source IDS so that we can populate the Edge table
    INSERT INTO [dbo].[DataEntity]
    OUTPUT INSERTED.$NODE_ID AS TOID INTO @NodeIDs(ID)
    SELECT
        value AS [ColumnName],
        @Table AS [TableName],
        @Database AS [DatabaseName],
        @System AS [SystemName],
        GETDATE() AS [CreatedDt]

    FROM  
        STRING_SPLIT(@ColumnList, ',');

    SELECT ID FROM @NodeIDs;    
    RETURN 
END

Now that we have a procedure to create our nodes, we will create another procedure to create the edges.

Create Edges Procedure

We need to pass a list of procedure a list of node ids to insert into the [dbo].[DataFlowsTo] table so we will create a user defined type to store and pass this information.

/* Create a table type in order to pass a list of Node IDs to this procedure*/
DROP TYPE IF EXISTS dbo.NodeIDTableType
CREATE TYPE dbo.NodeIDTableType  AS TABLE  ( ID NVARCHAR(1000) );

GO

After the user defined table type is created we can create the procedure to populate the edge table.

DROP PROCEDURE IF EXISTS dbo.Create_Edges
GO

CREATE PROCEDURE dbo.Create_Edges

    @Source  NodeIDTableType READONLY,
    @Target  NodeIDTableType READONLY,
    @Process VARCHAR(MAX)
AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

   --Get the FROM and TO node ids into a common table exppression and populate the edge table in batch.
   */
   
    WITH CTE (TOID, FROMID) AS
    (
        SELECT 
            A.FROMID,
            B.TOID
        FROM
            (SELECT ID AS FROMID, ROW_NUMBER() OVER(ORDER BY ID ASC) as RowNum FROM @Source) as A
        JOIN 
            (SELECT ID AS TOID, ROW_NUMBER() OVER(ORDER BY ID ASC) as RowNum FROM @Target) as B
        ON A.RowNum = B.RowNum
    )
    
    --Insert Lineage data into DataFlowsTo Edge table
     INSERT INTO [dbo].[DataFlowsTo] ($from_id, $to_id, ProcessName)
     SELECT CTE.TOID, CTE.FROMID, @Process FROM CTE;

    
END

In case you are wondering I used a common table expression (CTE) so that the edge records could be created in bulk rather than one at a time.

Create Data Lineage Procedure

This is the final procedure which checks to see if the source or target is new and calls the procedures above as required. The conditional logic check is premised on the assumption a the combination of system name, database name, table name and column name is unique.

DROP PROCEDURE IF EXISTS dbo.Create_Data_Lineage
GO
USE [DataLineage]
GO


CREATE PROCEDURE [dbo].[Create_Data_Lineage] 

    --Source data
    @SourceSystem VARCHAR(MAX),
    @SourceDatabase VARCHAR(MAX),
    @SourceTable VARCHAR(MAX),
    @SourceColumnList VARCHAR(MAX),

    --Target data
    @TargetSystem VARCHAR(MAX),
    @TargetDatabase VARCHAR(MAX),
    @TargetTable VARCHAR(MAX),
    @TargetColumnList VARCHAR(MAX),

    @ProcessName VARCHAR(MAX)

AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON;

        
    --DECLARE @SourceIDs TABLE (ID NVARCHAR(1000));
    --DECLARE @TargetIDs TABLE (ID NVARCHAR(1000));
    
    DECLARE @SourceIDs NodeIDTableType;
    DECLARE @TargetIDs NodeIDTableType;

    
    --Prepare the list of fields by removing any spaces or tabs between the comma seperated list of source and target columns
    SET @SourceColumnList = REPLACE(REPLACE(@SourceColumnList,' ', ''), char(9), '');
    SET @TargetColumnList = REPLACE(REPLACE(@TargetColumnList,' ', ''), char(9), '');

    --Check for existing sources , if found use those id's otherwise create new nodes and use new IDs
    INSERT INTO @SourceIDs
    SELECT 
        $NODE_ID
    FROM 
        [dbo].[DataEntity] DE
    INNER JOIN 
            (SELECT
                value AS [ColumnName],
                @SourceTable AS [TableName],
                @SourceDatabase AS [DatabaseName],
                @SourceSystem AS [SystemName]
            FROM  
                STRING_SPLIT(@SourceColumnList, ',')
            ) SRC
    ON
        DE.[ColumnName] = SRC.[ColumnName]
    AND 
        DE.[TableName] = SRC.[TableName]
    AND
        DE.[DatabaseName] = SRC.[DatabaseName]
    AND
        DE.[SystemName] = SRC.[SystemName];

    --Check for existing  targets, if found use those id's otherwise create new nodes and use new IDs
    INSERT INTO @TargetIDs
    SELECT 
        $NODE_ID
    FROM 
        [dbo].[DataEntity] DE
    INNER JOIN 
            (SELECT
                value AS [ColumnName],
                @TargetTable AS [TableName],
                @TargetDatabase AS [DatabaseName],
                @TargetSystem AS [SystemName]
            FROM  
                STRING_SPLIT(@TargetColumnList, ',')
            ) TRGT
    ON
        DE.[ColumnName] = TRGT.[ColumnName]
    AND 
        DE.[TableName] = TRGT.[TableName]
    AND
        DE.[DatabaseName] = TRGT.[DatabaseName]
    AND
        DE.[SystemName] = TRGT.[SystemName];

    IF (NOT EXISTS (SELECT 1 FROM @SourceIDs)) AND (NOT EXISTS (SELECT 1 FROM @TargetIDs))
        BEGIN

            --Create source nodes
            INSERT @SourceIDs
            EXEC  dbo.CREATE_NODES 
                    @System = @SourceSystem,
                    @Database = @SourceDatabase,
                    @Table = @SourceTable,
                    @ColumnList = @SourceColumnList;
        
            --Create target nodes
            INSERT @TargetIDs
            EXEC  dbo.CREATE_NODES 
                    @System = @TargetSystem,
                    @Database = @TargetDatabase,
                    @Table = @TargetTable,
                    @ColumnList = @TargetColumnList;
        
        
            --Create edges between source and target
            EXEC dbo.Create_Edges @Source = @SourceIDs, @Target = @TargetIDs, @Process = @ProcessName;
        END
    ELSE IF (EXISTS (SELECT 1 FROM @SourceIDs)) AND (NOT EXISTS (SELECT 1 FROM @TargetIDs))
        BEGIN
        
            --create target nodes
            INSERT @TargetIDs
            EXEC  dbo.CREATE_NODES 
                    @System = @TargetSystem,
                    @Database = @TargetDatabase,
                    @Table = @TargetTable,
                    @ColumnList = @TargetColumnList;

            --Create edges between source and target
            EXEC dbo.Create_Edges @Source = @SourceIDs, @Target = @TargetIDs, @Process = @ProcessName;
        END
    ELSE IF (NOT EXISTS (SELECT 1 FROM @SourceIDs)) AND (EXISTS (SELECT 1 FROM @TargetIDs))
        BEGIN
        
            --create source nodes
            INSERT @SourceIDs
            EXEC  dbo.CREATE_NODES 
                    @System = @SourceSystem,
                    @Database = @SourceDatabase,
                    @Table = @SourceTable,
                    @ColumnList = @SourceColumnList;

            --Create edges between source and target
            EXEC dbo.Create_Edges @Source = @SourceIDs, @Target = @TargetIDs, @Process = @ProcessName
        END
    ELSE 
        --No new nodes required
        --Create edges between source and target
        EXEC dbo.Create_Edges @Source = @SourceIDs, @Target = @TargetIDs, @Process = @ProcessName
    

END
GO

Summary

In this article we have created the database procedures to simplify the process of creating the necessary node and edge records to capture data lineage between source and target fields.

In the next article I will cover how to call these procedures and query the graph tables to answer data lineage questions.

Hopefully you have found this to be another practical post.

Until next time.

Anthony

Extend your information reach without over stretching by virtualizing data using SQL Server 2019 and MongoDB – Part 3 Setup Polybase

This is the third post in a series in which I explain how to use Polybase to connect SQL Server to Mongo DB in order to have a modern data ecosystem that caters to both structured and unstructured data. By leveraging Polybase you can centralize access without moving data and deliver a beast of breed solution for all of your data needs.

In my previous post I walked through how to spin up a SQL Server 2019 Azure VM and install Polybase. In this post I will show you how to setup Polybase to access a collection in MongoDB. This is the glue between MongoDB and SQL Server 2019. Conceptually this is the arrow in the diagram below.

First, I will show you how to setup an unsecure connection and then I will show you how to secure it with basic authentication.

Verify that MongoDB is up and running

Confirm that Mongo DB is up and running. As specified in my prior article you can use Studio 3T to connect or you can tunnel directly in using SSH and connect to MongoDB through PuTTY. If you shutdown the VM you will need to restart MongoDB using the command.

sudo service mongod restart

To run this command you will need to use PuTTY to tunnel in. Details on how to do this can be found in this article.

Configure polybase

Connect to the SQL Server instance. You can RDP into the VM or connect in from your local workstation. I connected in directly from my laptop using Azure Data Studio a nice light weight database tool.

Enable Polybase

Once connected you will need to turn on Polybase. Execute the following command in the MASTER database.

USE MASTER
exec sp_configure @configname = 'polybase enabled', @configvalue =1;
GO

RECONFIGURE WITH OVERRIDE;

Create Database

Next you will need to create a database. Execute the following SQL command to create a database called TEST.

CREATE
DATABASE TEST
GO

USE TEST
GO

The following commands all need to be executed in the new Test database that was just created with the command above.

Create External Data Source

Now you will need to create an external data source. I called mine MongoDBSource.

CREATE EXTERNAL DATA SOURCE MongoDBSource
WITH (
LOCATION='mongodb://40.85.255.249:27017',
CONNECTION_OPTIONS ='ssl=false;'
);
GO

Make sure that you modify the LOCATION parameter so that you specify the IP or name of the server that is running MongoDB.

Also you will need to add the CONNECTION_OPTIONS = ‘ssl=false;’ otherwise you will see the following error when you try to create the External Table.

Msg 105082, Level 16, State 1, Line 22

105082;Generic ODBC error: [Microsoft][MongoDBODBC] (110) Error from MongoDB Client: No suitable servers found (`serverSelectionTryOnce` set): [connection closed calling ismaster on ‘40.85.255.249:27017’] (Error Code: 13053) Additional error <2>: ErrorMsg: [Microsoft][MongoDBODBC] (110) Error from MongoDB Client: No suitable servers found (`serverSelectionTryOnce` set): [connection closed calling ismaster on ‘40.85.255.249:27017’] (Error Code: 13053), SqlState: HY000, NativeError: 110 .

Create External Table

The last thing we need to do is create an external table.

CREATE EXTERNAL TABLE Test(
[_id] NVARCHAR(24),
[x] FLOAT(53)
)
WITH (
LOCATION='test.testData',
DATA_SOURCE= MongoDBSource
);

Common errors

If you try to implicitly convert the [x] FLOAT(53) column to an int you will see the following error.

Msg 105083, Level 16, State 1, Line 24

105083;The following columns in the user defined schema are incompatible with the external table schema for table ‘Test2’: user defined column type: ([x] INT) vs. detected external table column type: ([x] FLOAT(53)). The detected external table schema is: ([_id] NVARCHAR(24) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL, [x] FLOAT(53))

This is because SQL Server requires a schema on read with strong type casting.

In addition, if you try to create the table without all of the “columns” that reside in the collection by using the following SQL command.

CREATE
EXTERNAL
TABLE Test2(
 [x] FLOAT(53)
)
WITH (
LOCATION='test.testData',
DATA_SOURCE= MongoDBSource
);

You will get the following error.

Msg 105075, Level 16, State 1, Line 24

105075;The user specified schema column count is 1, which varies from the external table schema column count of 2. The detected external table schema is: ([_id] NVARCHAR(24) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL, [x] FLOAT(53))

Again, this is because the current version of PolyBase in SQL Server requires a table structure that matches the collection structure in MongoDB.

Once the table is created you can query it just as you would any other table in SQL Server.

Select *
from [dbo].[Test]

Your results should look similar to the image below.

By default the PUSHDOWN predicate is applied so that the MongoDB is used for query execution allowing for optimum performance by distributing the compute to the best location/technology for the job.

Next let’s add some basic authentication so that our connection is a bit more secure.

Securing the connection with basic Authentication

Using PuTTY log back in the MongoDB VM. Once connected to the VM log into MongoDB by typing in the following command.

mongo

Once in the MongoDB shell execute the following command.

use test
db.createUser(
{
user: “mytestuser”,
pwd: “mytestuser”,
roles: [ { role: “readWrite”, db: “test” } ]
}
)

You should see the following response if the command is successful.

Successfully added user:
{
 "user" : "mytestuser",
 "pwd" : "mytestuser",
 "roles" : [
 {
 "role" : "readWrite",
 "db" : " test "
 }
 ]
}

This creates a user called mytestuser with the password mytestuser. You should probably use a more secure id and password but this is sufficient for the purposes of this article.

Enable authentication in MongoDB

Exit out of Mongo and run the following command.

sudo nano /etc/mongod.conf

Modify the configuration file by adding the tag authorization: enabled under the security section.

Exit and save the config file and then restart mongo.

sudo service mongod restart

Modify SQL Server

Now that we have made the necessary changes in MongoDB we need to add authentication information in SQL Server.

Log into SQL Server and create a master key. Execute the following SQL command to create a master key.

USE TEST

CREATE MASTER KEY ENCRYPTION BY PASSWORD = 'Password123!'
GO

Next create a database scoped credential.

CREATE DATABASE SCOPED CREDENTIAL MongoDB
WITH IDENTITY ='mytestuser', SECRET = 'mytestuser';

GO

As you can see in the command above the IDENTITY and SECRET must match the user and pwd in the MongoDB command we used to create the user.

Last, we will drop and recreate the external data source and table using the following commands.

DROP EXTERNAL DATA SOURCE MongoDBSource

CREATE EXTERNAL DATA SOURCE MongoDBSource
WITH (
  LOCATION = 'mongodb://40.85.255.249:27017', 
  CREDENTIAL = MongoDB,
  CONNECTION_OPTIONS = 'ssl=false;'
);

GO

--Notice how the CREDENTIAL argument has been added to the create command above.

DROP EXTERNAL TABLE Test
CREATE EXTERNAL TABLE Test(
[_id] NVARCHAR(24),
[x] FLOAT(53)
)
WITH (
LOCATION='test.testData',
DATA_SOURCE= MongoDBSource
);

Now you are using an account to access the database in MongoDB. The next step would be to enable SSL in MongoDB so that the CONNECTION_OPTIONS ‘ssl=false;’ can be removed and a secure connection established between SQL Server and MongoDB. The details on how to do it is beyond the scope of this article for instructions on how to enable SSL in MongoDB you can refer to the following guide.

https://docs.mongodb.com/manual/tutorial/configure-ssl/

The setup that I have documented in this series can be done on premise or in the cloud using VMs as I have done.

Hopefully you have found this to be another practical post.

Until next time.

Anthony