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Slow query logs in Azure Database for MySQL - Flexible Server

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In Azure Database for MySQL Flexible Server, the slow query log is available to users to configure and access. Slow query logs are disabled by default and can be enabled to assist with identifying performance bottlenecks during troubleshooting.

For more information about the MySQL slow query log, see the slow query log section in the MySQL engine documentation.

Configure slow query logging

By default, the slow query log is disabled. To enable logs, set the slow_query_log server parameter to ON. This can be configured using the Azure portal or Azure CLI.

Other parameters you can adjust to control slow query logging behavior include:

  • long_query_time: log a query if it takes longer than long_query_time (in seconds) to complete. The default is 10 seconds. Server parameter long_query_time applies globally to all newly established connections in MySQL. However, it doesn't affect threads that are already connected. It's recommended to reconnect to Azure Database for MySQL Flexible Server from the application, or restarting the server will help clear out threads with older values of "long_query_time" and apply the updated parameter value.
  • log_slow_admin_statements: determines if administrative statements (ex. ALTER_TABLE, ANALYZE_TABLE) are logged.
  • log_queries_not_using_indexes: determines if queries that don't use indexes are logged.
  • log_throttle_queries_not_using_indexes: limits the number of non-indexed queries that can be written to the slow query log. This parameter takes effect when log_queries_not_using_indexes is set to ON

Important

If your tables are not indexed, setting the log_queries_not_using_indexes and log_throttle_queries_not_using_indexes parameters to ON might affect MySQL performance since all queries running against these non-indexed tables will be written to the slow query log.

See the MySQL slow query log documentation for full descriptions of the slow query log parameters.

Access slow query logs

Slow query logs are integrated with Azure Monitor diagnostic settings. Once you've enabled slow query logs on your Azure Database for MySQL Flexible Server instance, you can emit them to Azure Monitor logs, Event Hubs, or Azure Storage. To learn more about diagnostic settings, see the diagnostic logs documentation. To learn more about how to enable diagnostic settings in the Azure portal, see the slow query log portal article.

Note

Premium Storage accounts are not supported if you are sending the logs to Azure storage via diagnostics and settings.

The following table describes the output of the slow query log. Depending on the output method, the fields included and the order in which they appear might vary.

Property Description
TenantId Your tenant ID
SourceSystem Azure
TimeGenerated [UTC] Time stamp when the log was recorded in UTC
Type Type of the log. Always AzureDiagnostics
SubscriptionId GUID for the subscription that the server belongs to
ResourceGroup Name of the resource group the server belongs to
ResourceProvider Name of the resource provider. Always MICROSOFT.DBFORMYSQL
ResourceType Servers
ResourceId Resource URI
Resource Name of the server
Category MySqlSlowLogs
OperationName LogEvent
Logical_server_name_s Name of the server
start_time_t [UTC] Time the query began
query_time_s Total time in seconds the query took to execute
lock_time_s Total time in seconds the query was locked
user_host_s Username
rows_sent_s Number of rows sent
rows_examined_s Number of rows examined
last_insert_id_s last_insert_id
insert_id_s Insert ID
sql_text_s Full query
server_id_s The server's ID
thread_id_s Thread ID
\_ResourceId Resource URI

Note

For sql_text_s, log will be truncated if it exceeds 2048 characters.

Analyze logs in Azure Monitor Logs

Once your slow query logs are piped to Azure Monitor Logs through Diagnostic Logs, you can perform further analysis of your slow queries. Below are some sample queries to help you get started. Make sure to update the below with your server name.

  • Queries longer than 10 seconds on a particular server

    AzureDiagnostics
| where Resource  == '<your server name>'
| where Category == 'MySqlSlowLogs'
| project TimeGenerated, Resource , event_class_s, start_time_t , query_time_d, sql_text_s
| where query_time_d > 10

  • List top 5 longest queries on a particular server

    AzureDiagnostics
| where Resource  == '<your server name>'
| where Category == 'MySqlSlowLogs'
| project TimeGenerated, Resource , event_class_s, start_time_t , query_time_d, sql_text_s
| order by query_time_d desc
| take 5

  • Summarize slow queries by minimum, maximum, average, and standard deviation query time on a particular server

    AzureDiagnostics
| where Resource  == '<your server name>'
| where Category == 'MySqlSlowLogs'
| project TimeGenerated, Resource , event_class_s, start_time_t , query_time_d, sql_text_s
| summarize count(), min(query_time_d), max(query_time_d), avg(query_time_d), stdev(query_time_d), percentile(query_time_d, 95) by Resource

  • Graph the slow query distribution on a particular server

    AzureDiagnostics
| where Resource  == '<your server name>'
| where Category == 'MySqlSlowLogs'
| project TimeGenerated, Resource , event_class_s, start_time_t , query_time_d, sql_text_s
| summarize count() by Resource , bin(TimeGenerated, 5m)
| render timechart

  • Display queries longer than 10 seconds across all Azure Database for MySQL Flexible Server instances with Diagnostic Logs enabled

    AzureDiagnostics
| where Category == 'MySqlSlowLogs'
| project TimeGenerated, Resource , event_class_s, start_time_t , query_time_d, sql_text_s
| where query_time_d > 10

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