Error Code 45172 – Overview

Error Code 45172 in Azure SQL Database typically occurs when the database experiences resource constraints, primarily due to high memory or session limits. This error often manifests when operations or queries exceed allocated memory resources, interrupting query execution or session management.

Summary Table

Background

Azure SQL Database enforces memory and session limits to optimize resource usage across multiple databases. Error 45172 occurs when these limits are surpassed, usually due to high memory consumption or an excessive number of active sessions. Memory-intensive queries, excessive session counts, and long-running transactions are typical culprits for this error.

Error Explanation

The error message for Error Code 45172 typically reads:

Error 45172: Resource limit exceeded due to high memory or session usage.

This error indicates that the Azure SQL Database is unable to execute or manage queries and sessions within the allocated resources, causing interruptions to ongoing operations.

Common Causes

1. Memory-Intensive Queries: Complex queries with large joins, subqueries, or high data processing demands can exhaust memory resources.
2. Excessive Active Sessions: Too many simultaneous connections or open transactions can use up the available session limit.
3. Long-Running Transactions: Transactions that lock resources for an extended period can monopolize memory and block other queries.
4. Improper Database Scaling: Databases not scaled to match workload demands may run out of resources more easily.

Steps to Troubleshoot and Resolve Error Code 45172

Step 1: Diagnose Active Queries and Sessions

To identify sessions that consume excessive resources, use queries to list active sessions with high memory or long runtime:

• Example Query:

SELECT
    session_id,
    login_name,
    status,
    memory_usage,
    total_elapsed_time
FROM sys.dm_exec_sessions
WHERE is_user_process = 1
ORDER BY memory_usage DESC;

• Purpose: This query provides a list of active user sessions, sorted by memory usage, helping to identify high-resource sessions.

Step 2: Terminate High-Memory or Long-Running Sessions

For sessions that use significant memory or run for too long, consider terminating them to free up resources.

• Example Query to Identify and Terminate Sessions:

SELECT
    session_id,
    status,
    memory_usage,
    cpu_time,
    total_elapsed_time
FROM sys.dm_exec_requests
ORDER BY memory_usage DESC;

• Terminate Session:

KILL session_id;

• Replace session_id with the ID of the specific high-resource session.

Step 3: Optimize Memory-Intensive Queries

Memory-intensive queries can be a major source of this error. Consider optimizing these queries by reducing complexity, breaking them into smaller components, or adding indexes.

• Update Statistics:

UPDATE STATISTICS table_name;

• Purpose: Updating statistics can optimize query execution plans, thereby reducing memory usage.

Step 4: Scale Database Resources

If resource usage regularly exceeds limits, consider scaling up the database to provide additional DTUs (Database Transaction Units) or vCores.

• Scale Options:
  • Scale Up: Increase DTUs or vCores for more memory and processing power.
  • Elastic Pools: If you manage multiple databases, use an elastic pool to share resources more efficiently.

Step 5: Implement Connection Pooling and Limit Session Usage

Connection pooling limits the number of active sessions by reusing connections, reducing the likelihood of session overload.

• Example Code for Connection Pooling in .NET:

var connection = new SqlConnection("YourConnectionString;Pooling=true;");

Step 6: Implement Retry Logic for Error Handling

When temporary resource limits cause failures, using retry logic can help handle such intermittent issues.

• Example Retry Logic in C#:

int retryCount = 0;
while (retryCount < maxRetries)
{
    try
    {
        // Execute your SQL query here
        break;
    }
    catch (SqlException ex)
    {
        if (ex.Number == 45172)
        {
            retryCount++;
            Thread.Sleep(TimeSpan.FromSeconds(2));
        }
        else
        {
            throw;
        }
    }
}

Step 7: Monitor Resource Metrics and Set Alerts

Regular monitoring allows you to proactively manage resource usage. Azure Monitor can track metrics like memory usage, active sessions, and DTU consumption.

• Steps:
  • In Azure Portal, navigate to SQL Database > Monitoring > Insights.
  • Set up Alerts for thresholds close to resource limits to proactively address potential issues.

Workarounds

1. Limit Active Sessions: Adjust application code to manage session counts efficiently or use connection pooling.
2. Optimize Queries: Reducing memory demand in queries can significantly lower overall resource usage.
3. Use Backups and Restore as Needed: For consistent performance, maintain periodic backups to avoid repeated execution of memory-heavy queries.

Solutions

1. Monitor and Diagnose Metrics: Use Azure monitoring tools to keep track of query and session metrics.
2. Scale Up or Scale Out: Upgrade DTUs or vCores based on demand.
3. Optimize Transactions: Reduce complexity in long-running transactions or manage locks to avoid excessive memory use.
4. Retry Logic: Adding retry logic in application code handles intermittent resource-related errors gracefully.

Example Scenario

Suppose you encounter Error Code 45172 while executing a memory-intensive report query.

1. Step 1: Run a query to list active sessions and memory usage.
   • You identify the report query consuming significant memory.
2. Step 2: Terminate the session if needed using the KILL session_id command.
3. Step 3: Optimize the report query by adding indexes and updating statistics on related tables.
4. Step 4: Scale the database by increasing DTUs to accommodate memory requirements.
5. Step 5: Enable connection pooling to manage session limits more effectively.
6. Step 6: Set up alerts for high memory usage in Azure Monitor, ensuring prompt action on potential issues in the future.

By following these steps, you can effectively manage and resolve Error Code 45172 in Azure SQL Database, ensuring resource stability and minimizing disruptions.