Assess query performance using Query Store

In this exercise, learn how to query performance metrics using the Query Store in Azure Database for PostgreSQL.

Before you start

You need your own Azure subscription to complete this exercise. If you don’t have an Azure subscription, you can create an Azure free trial.

Additionally, you need to have the following installed on your computer:

Visual Studio Code.
Postgres Visual Studio Code Extension by Microsoft.
Azure CLI.
Git.

Create the exercise environment

In this and later exercises, you use a Bicep script to deploy the Azure Database for PostgreSQL - Flexible Server and other resources into your Azure subscription. The Bicep scripts are located in the /Allfiles/Labs/Shared folder of the GitHub repository you cloned earlier.

Download and install Visual Studio Code and the PostgreSQL extension

If you don’t have Visual Studio Code installed:

In a browser, navigate to Download Visual Studio Code and select the appropriate version for your operating system.
Follow the installation instructions for your operating system.
Open Visual Studio Code.
From the left menu, select Extensions to display the Extensions panel.
In the search bar, enter PostgreSQL. The PostgreSQL extension for Visual Studio Code icon is displayed. Make sure you select the one by Microsoft.
Select Install. The extension installs.

Download and install Azure CLI and Git

If you don’t have Azure CLI or Git installed:

In a browser, navigate to Install the Azure CLI and follow the instructions for your operating system.
In a browser, navigate to Download and install Git and follow the instructions for your operating system.

Download the exercise files

If you already cloned the GitHub repository containing the exercise files, Skip downloading the exercise files.

To download the exercise files, you clone the GitHub repository containing the exercise files to your local machine. The repository contains all the scripts and resources you need to complete this exercise.

Open Visual Studio Code if it isn’t already open.
Select Show all commands (Ctrl+Shift+P) to open the command palette.
In the command palette, search for Git: Clone and select it.
In the command palette, enter the following to clone the GitHub repo containing exercise resources and press Enter:
```
 https://github.com/MicrosoftLearning/mslearn-postgresql.git
```
Follow the prompts to select a folder to clone the repository into. The repository is cloned into a folder named mslearn-postgresql in the location you selected.
When asked if you want to open the cloned repository, select Open. The repository opens in Visual Studio Code.

Deploy resources into your Azure subscription

If your Azure resources are already installed, Skip deploying resources.

This step guides you through using Azure CLI commands from Visual Studio Code to create a resource group and run a Bicep script to deploy the Azure services necessary for completing this exercise into your Azure subscription.

📝 If you are doing multiple modules in this learning path, you can share the Azure environment between them. In that case, you only need to complete this resource deployment step once.

Open Visual Studio Code if it isn’t already open, and open the folder where you cloned the GitHub repository.
Expand the mslearn-postgresql folder in the Explorer pane.
Expand the Allfiles/Labs/Shared folder.
Right-click the Allfiles/Labs/Shared folder and select Open in Integrated Terminal. This selection opens a terminal window at in the Visual Studio Code window.
The terminal might open a powershell window by default. For this section of the lab, you want to use the bash shell. Besides the + icon, there’s a dropdown arrow. Select it and select Git Bash or Bash from the list of available profiles. This selection opens a new terminal window with the bash shell.

📝 You can close the powershell terminal window if you want to, but it is not necessary. You can have multiple terminal windows open at the same time.
In the terminal window, run the following command to sign-in to your Azure account:
```
 az login
```
This command opens a new browser window prompting you to sign-in to your Azure account. After logging in, return to the terminal window.
Next, you run three commands to define variables to reduce redundant typing when using Azure CLI commands to create Azure resources. The variables represent the name to assign to your resource group (RG_NAME), the Azure region (REGION) into which resources are deployed, and a randomly generated password for the PostgreSQL administrator sign-in (ADMIN_PASSWORD).

In the first command, the region assigned to the corresponding variable is eastus, but you can also replace it with a location of your preference.
```
 REGION=eastus
```
The following command assigns the name to be used for the resource group that houses all the resources used in this exercise. The resource group name assigned to the corresponding variable is rg-learn-work-with-postgresql-$REGION, where $REGION is the location you previously specified. However, you can change it to any other resource group name that suits your preference or that you might already have.
```
 RG_NAME=rg-learn-work-with-postgresql-$REGION
```
The final command randomly generates a password for the PostgreSQL admin sign-in. Make sure you copy it to a safe place so that you can use it later to connect to your PostgreSQL flexible server.
```
 #!/bin/bash
    
 # Define array of allowed characters explicitly
 chars=( {a..z} {A..Z} {0..9} '!' '@' '#' '$' '%' '^' '&' '*' '(' ')' '_' '+' )
    
 a=()
 for ((i = 0; i < 100; i++)); do
     rand_char=${chars[$RANDOM % ${#chars[@]}]}
     a+=("$rand_char")
 done
    
 # Join first 18 characters without delimiter
 ADMIN_PASSWORD=$(IFS=; echo "${a[*]:0:18}")
    
 echo "Your randomly generated PostgreSQL admin user's password is:"
 echo "$ADMIN_PASSWORD"
 echo "Please copy it to a safe place, as you will need it later to connect to your PostgreSQL flexible server."
```
(Skip if using your default subscription.) If you have access to more than one Azure subscription, and your default subscription isn’t the one in which you want to create the resource group and other resources for this exercise, run this command to set the appropriate subscription, replacing the <subscriptionName|subscriptionId> token with either the name or ID of the subscription you want to use:
```
 az account set --subscription 16b3c013-d300-468d-ac64-7eda0820b6d3
```
(Skip if you’re using an existing resource group) Run the following Azure CLI command to create your resource group:
```
 az group create --name $RG_NAME --location $REGION
```
Finally, use the Azure CLI to execute a Bicep deployment script to provision Azure resources in your resource group:
```
 az deployment group create --resource-group $RG_NAME --template-file "Allfiles/Labs/Shared/deploy-postgresql-server.bicep" --parameters adminLogin=pgAdmin adminLoginPassword=$ADMIN_PASSWORD databaseName=adventureworks
```
The Bicep deployment script provisions the Azure services required to complete this exercise into your resource group. The resources deployed are an Azure Database for PostgreSQL - Flexible Server. The bicep script also creates the adventureworks database.

The deployment typically takes several minutes to complete. You can monitor it from the bash terminal or navigate to the Deployments page for the resource group you previously created and observe the deployment progress there.
Since the script creates a random name for the PostgreSQL server, you can find the name of the server by running the following command:
```
 az postgres flexible-server list --query "[].{Name:name, ResourceGroup:resourceGroup, Location:location}" --output table
```
Write down the name of the server, as you need it to connect to the server later in this exercise.

📝 You can also find the name of the server in the Azure portal. In the Azure portal, navigate to Resource groups and select the resource group you previously created. The PostgreSQL server is listed in the resource group.

Troubleshooting deployment errors

You might encounter a few errors when running the Bicep deployment script. The most common messages and the steps to resolve them are:

If you previously ran the Bicep deployment script for this learning path and then deleted the resources, you might receive an error message like the following if you’re attempting to rerun the script within 48 hours of deleting the resources:

  {"code": "InvalidTemplateDeployment", "message": "The template deployment 'deploy' is not valid according to the validation procedure. The tracking id is '4e87a33d-a0ac-4aec-88d8-177b04c1d752'. See inner errors for details."}
    
  Inner Errors:
  {"code": "FlagMustBeSetForRestore", "message": "An existing resource with ID '/subscriptions/{subscriptionId}/resourceGroups/rg-learn-postgresql-ai-eastus/providers/Microsoft.CognitiveServices/accounts/{accountName}' has been soft-deleted. To restore the resource, you must specify 'restore' to be 'true' in the property. If you don't want to restore existing resource, please purge it first."}

If you receive this message, modify the previous azure deployment group create command to set the restore parameter equal to true and rerun it.

If the selected region is restricted from provisioning specific resources, you must set the REGION variable to a different location and rerun the commands to create the resource group and run the Bicep deployment script.

  {"status":"Failed","error":{"code":"DeploymentFailed","target":"/subscriptions/{subscriptionId}/resourceGroups/{resourceGrouName}/providers/Microsoft.Resources/deployments/{deploymentName}","message":"At least one resource deployment operation failed. Please list deployment operations for details. Please see https://aka.ms/arm-deployment-operations for usage details.","details":[{"code":"ResourceDeploymentFailure","target":"/subscriptions/{subscriptionId}/resourceGroups/{resourceGroupName}/providers/Microsoft.DBforPostgreSQL/flexibleServers/{serverName}","message":"The resource write operation failed to complete successfully, because it reached terminal provisioning state 'Failed'.","details":[{"code":"RegionIsOfferRestricted","message":"Subscriptions are restricted from provisioning in this region. Please choose a different region. For exceptions to this rule please open a support request with Issue type of 'Service and subscription limits'. See https://review.learn.microsoft.com/en-us/azure/postgresql/flexible-server/how-to-request-quota-increase for more details."}]}]}}

If the lab requires AI resources, you might get the following error. This error occurs when the script is unable to create an AI resource due to the requirement to accept the responsible AI agreement. If that is the case, use the Azure portal user interface to create an Azure AI Services resource, and then rerun the deployment script.

  {"code": "InvalidTemplateDeployment", "message": "The template deployment 'deploy' is not valid according to the validation procedure. The tracking id is 'f8412edb-6386-4192-a22f-43557a51ea5f'. See inner errors for details."}
     
  Inner Errors:
  {"code": "ResourceKindRequireAcceptTerms", "message": "This subscription cannot create TextAnalytics until you agree to Responsible AI terms for this resource. You can agree to Responsible AI terms by creating a resource through the Azure Portal then trying again. For more detail go to https://go.microsoft.com/fwlink/?linkid=2164190"}

Install psql

Since we need to copy the data from the CSV file into the PostgreSQL database, we need to install psql on your local machine. If you already have psql installed, skip this section.

To check if psql is already installed in your environment, open command line/terminal, and run the command psql. If it returns a message like “psql: error: connection to server on socket…”, that means that the psql tool is already installed in your environment and there’s no need to reinstall it and you can skip this section.
Install psql.
In the setup wizard, follow the prompt until you reach the Select Components dialog box, select Command Line Tools. You can uncheck the other components if you aren’t planning to use them. Complete the installation by following the prompts.
Open a new command prompt or terminal window and run psql to verify that the installation was successful. If you see a message like “psql: error: connection to server on socket…”, that means that the psql tool is installed successfully. Otherwise, you might need to add the PostgreSQL bin directory to your system PATH variable.
1. If you’re using Windows, make sure to add the PostgreSQL bin directory to your system PATH variable. The bin directory is typically located at C:\Program Files\PostgreSQL\<version>\bin.
  1. You can check if the bin directory is in your PATH variable by running the command echo %PATH% in a command prompt and checking if the PostgreSQL bin directory is listed. If it isn’t, you can add it manually.
  2. To add it manually, right-click on the Start button.
  3. Select System and then select Advanced system settings.
  4. Select the Environment Variables button.
  5. Double-click on the Path variable in the System variables section.
  6. Select New, and add the path to the PostgreSQL bin directory.
  7. After adding it, close and reopen the command prompt for the changes to take effect.
2. If you’re using macOS or Linux, the PostgreSQL bin directory is typically located at /usr/local/pgsql/bin.
  1. You can check whether this directory is in your PATH environment variable by running echo $PATH in a terminal.
  2. If it’s not, you can add it by editing your shell configuration file, usually .bash_profile, .bashrc, or .zshrc, depending on your shell.

Populate the database with data

Once you verified that psql is installed, you can connect to your PostgreSQL server using the command line, by opening a command prompt or terminal window.

📝 If you are using Windows, you can use the Windows PowerShell or Command Prompt. If you are using macOS or Linux, you can use the Terminal application.

The syntax for connecting to the server is:

psql -h <servername> -p <port> -U <username> <dbname>

At the command prompt or terminal, enter --host=<servername>.postgres.database.azure.com where <servername> is the name of the Azure Database for PostgreSQL previously created.

You can find the Server name in Overview in the Azure portal or as an output from the bicep script or on the Azure portal.
```
psql -h <servername>.postgres.database.azure.com -p 5432 -U pgAdmin adventureworks
```
You’re prompted for the password for the admin account you previously copied.
You need to create a table within the database and populate it with sample data so you have information to work with as you review locking in this exercise.

Run the following command to create the production.workorder table for loading in data:

 DROP SCHEMA IF EXISTS production CASCADE;
 CREATE SCHEMA production;
    
 DROP TABLE IF EXISTS production.workorder;
 CREATE TABLE production.workorder
 (
     workorderid integer NOT NULL,
     productid integer NOT NULL,
     orderqty integer NOT NULL,
     scrappedqty smallint NOT NULL,
     startdate timestamp without time zone NOT NULL,
     enddate timestamp without time zone,
     duedate timestamp without time zone NOT NULL,
     scrapreasonid smallint,
     modifieddate timestamp without time zone NOT NULL DEFAULT now()
 )
 WITH (
     OIDS = FALSE
 )
 TABLESPACE pg_default;

Next, use the COPY command to load data from CSV files into the table you previously created. Start by running the following command to populate the production.workorder table:
```
 \COPY production.workorder FROM 'mslearn-postgresql/Allfiles/Labs/08/Lab8_workorder.csv' CSV HEADER
```
The command output should be COPY 72591, indicating that 72,591 rows were written into the table from the CSV file.
Close the command prompt or terminal window.

Connect to the database with Visual Studio Code

Open Visual Studio Code if it isn’t already opened and open the folder where you cloned the GitHub repository.
Select the PostgreSQL icon in the left menu.

📝 If you do not see the PostgreSQL icon, select the Extensions icon and search for PostgreSQL. Select the PostgreSQL extension by Microsoft and select Install.
If you already created a connection to your PostgreSQL server, skip to the next step. To create a new connection:
1. In the PostgreSQL extension, select + Add Connection to add a new connection.
2. In the NEW CONNECTION dialog box, enter the following information:
  - Server name: <your-server-name>.postgres.database.azure.com
  - Authentication type: Password
  - User name: pgAdmin
  - Password: The random password you previously generated.
  - Check the Save password checkbox.
  - Connection name: <your-server-name>
3. Test the connection by selecting Test Connection. If the connection is successful, select Save & Connect to save the connection, otherwise review the connection information, and try again.
If not already connected, select Connect for your PostgreSQL server. You’re connected to the Azure Database for PostgreSQL server.
Expand the Server node and its databases. The existing databases are listed.
Open Visual Studio Code if it isn’t already open.
Bring up the command palette (Ctrl+Shift+P) and select PGSQL: New Query. Select the new connection you created from the list in the command palette. If it asks for a password, enter the password you created for the new role.
On the lower right of the New Query window, make sure the connection is green. If it isn’t, it should say PGSQL Disconnected. Select the PGSQL Disconnected text and then select your PostgreSQL server connection from the list in the command palette. If it asks for a password, enter the password you previously generated.
On the New Query window, copy, highlight, and execute the following SQL statement:
```
 SELECT current_database();
```
If the current database isn’t set to adventureworks, you need to change the database to adventureworks. To change the database, select the ellipsis in the menu bar with the run icon and selecting Change PostgreSQL Database. Select adventureworks from the list of databases. Verify that the database is now set to adventureworks by running the SELECT current_database(); statement.
On the New Query window, copy, highlight, and execute the following SQL statement:
```
 SELECT * FROM production.workorder;
```
minimize the New Query window, we return to it later in this exercise.

Task 1: Turn on query capture mode

Navigate to the Azure portal and sign in.
Select your Azure Database for PostgreSQL server for this exercise.
In Settings, select Server parameters.
Navigate to the pg_qs.query_capture_mode setting.
Select TOP.
Navigate to pgms_wait_sampling.query_capture_mode, select ALL, and select Save.
Wait for the server parameters to update.

View pg_stat data

Return to Visual Studio Code and select the New Query window we previously opened.

Replace the existing query with the following one and select Run.

 SELECT 
     pid,                    -- Process ID of the server process
     datid,                  -- OID of the database
     datname,                -- Name of the database
     usename,                -- Name of the user
     application_name,       -- Name of the application connected to the database
     client_addr,            -- IP address of the client
     client_hostname,        -- Hostname of the client (if available)
     client_port,            -- TCP port number that the client is using for the connection
     backend_start,          -- Timestamp when the backend process started
     xact_start,             -- Timestamp of the current transaction start, if any
     query_start,            -- Timestamp when the current query started, if any
     state_change,           -- Timestamp when the state was last changed
     wait_event_type,        -- Type of event the backend is waiting for, if any
     wait_event,             -- Event that the backend is waiting for, if any
     state,                  -- Current state of the session (e.g., active, idle, etc.)
     backend_xid,            -- Transaction ID, if active
     backend_xmin,           -- Transaction ID that the process is working with
     query,                  -- Text of the query being executed
     encode(backend_type::bytea, 'escape') AS backend_type,           -- Type of backend (e.g., client backend, autovacuum worker). We use encode(…, 'escape') to safely display raw data with invalid characters by converting it into a readable format, doing this prevents a UTF-8 conversion error in Visual Studio Code.
     leader_pid,             -- PID of the leader process, if this is a parallel worker
     query_id               -- Query ID (added in more recent PostgreSQL versions)
 FROM pg_stat_activity;

Review the metrics that are available.
Leave Visual Studio Code open for the next task.

Task 2: Examine query statistics

📝 For a newly created database, there might be limited statistics, if any. If you wait for 30 minutes there will be statistics from background processes.

On the New Query window, copy, highlight, and execute the following SQL statement:
```
 SELECT current_database();
```
You need to change the database to azure_sys. To change the database, select the ellipsis in the menu bar with the run icon and selecting Change PostgreSQL Database. Select azure_sys from the list of databases. Verify that the database is now set to azure_sys by running the SELECT current_database(); statement.

On the New Query window, copy, highlight, and execute the following SQL statements:

 SELECT * FROM query_store.query_texts_view;

 SELECT * FROM query_store.qs_view;

 SELECT * FROM query_store.runtime_stats_view;

 SELECT * FROM query_store.pgms_wait_sampling_view;

Review the metrics that are available.

Clean-Up

If you don’t need this PostgreSQL server anymore for other exercises, to avoid incurring unnecessary Azure costs, delete the resource group created in this exercise.
If you want to keep the PostgreSQL server running, you can leave it running. If you don’t want to leave it running, you can stop the server to avoid incurring unnecessary costs in the bash terminal. To stop the server, run the following command:
```
 az postgres flexible-server stop --name <your-server-name> --resource-group $RG_NAME
```
Replace <your-server-name> with the name of your PostgreSQL server.

📝 You can also stop the server from the Azure portal. In the Azure portal, navigate to Resource groups and select the resource group you previously created. Select the PostgreSQL server and then select Stop from the menu.
If needed, delete the git repository you cloned earlier.

In this exercise, you learned how to assess query performance using Query Store in Azure Database for PostgreSQL. You also learned how to view pg_stat data and examine query statistics.