Mysql: Select From Information_schema.STATISTICS Hanging Or Slow? Never Saw A Result

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Introduction

As a MySQL administrator, it's essential to monitor and analyze the performance of your database. One of the critical components of database performance is the statistics of the tables, which provide valuable insights into the data distribution and indexing. However, when trying to retrieve these statistics using the SELECT statement from the information_schema.STATISTICS table, you may encounter a situation where the query hangs or takes an excessively long time to complete, never returning a result. In this article, we'll explore the possible causes of this issue and provide solutions to resolve it.

Understanding the Problem

The information_schema.STATISTICS table provides a wealth of information about the tables in your database, including the index statistics. However, when you run a SELECT statement on this table, you may encounter a situation where the query never completes or takes an inordinate amount of time to return a result. This can be frustrating, especially when you need to analyze the performance of your database.

Possible Causes

There are several possible causes of this issue, including:

  • Innodb_stats_on_metadata: This variable controls whether InnoDB collects statistics on metadata operations. If this variable is set to 1, InnoDB collects statistics on metadata operations, which can lead to performance issues when retrieving statistics from the information_schema.STATISTICS table.
  • Large number of tables or indexes: If your database has a large number of tables or indexes, retrieving statistics from the information_schema.STATISTICS table can be a time-consuming process.
  • Index corruption: Corrupted indexes can lead to performance issues when retrieving statistics from the information_schema.STATISTICS table.
  • Server load: High server load can cause performance issues when retrieving statistics from the information_schema.STATISTICS table.

Solutions

To resolve the issue of a hanging or slow query when retrieving statistics from the information_schema.STATISTICS table, you can try the following solutions:

1. Set innodb_stats_on_metadata to 0

As mentioned earlier, setting innodb_stats_on_metadata to 0 can resolve the issue of a hanging or slow query when retrieving statistics from the information_schema.STATISTICS table. To set this variable, you can use the following command:

SET GLOBAL innodb_stats_on_metadata = 0;

2. Optimize the query

If you're retrieving statistics from a large number of tables or indexes, you can optimize the query by using a WHERE clause to filter the results. For example:

SELECT *
FROM information_schema.STATISTICS
WHERE TABLE_NAME = 'your_table_name';

3. Check for index corruption

Corrupted indexes can lead to performance issues when retrieving statistics from the information_schema.STATISTICS table. To check for index corruption, you can use the following command:

CHECK TABLE your_table_name;

4. Reduce server load

High server load can cause performance issues when retrieving statistics from the information_schema.STATISTICS table. To reduce server load, you can try the following:

  • Close unnecessary connections: Close any unnecessary connections to the database to reduce the load on the server.
  • Optimize queries: Optimize any long-running queries to reduce the load on the server.
  • Add more resources: If the server is underpowered, consider adding more resources, such as CPU or memory, to improve performance.

Conclusion

In conclusion, a hanging or slow query when retrieving statistics from the information_schema.STATISTICS table can be caused by several factors, including innodb_stats_on_metadata, large number of tables or indexes, index corruption, and server load. By setting innodb_stats_on_metadata to 0, optimizing the query, checking for index corruption, and reducing server load, you can resolve this issue and retrieve statistics from the information_schema.STATISTICS table efficiently.

Additional Tips

Here are some additional tips to help you troubleshoot and resolve the issue of a hanging or slow query when retrieving statistics from the information_schema.STATISTICS table:

  • Use the EXPLAIN statement: Use the EXPLAIN statement to analyze the query plan and identify any performance issues.
  • Use the SHOW PROCESSLIST statement: Use the SHOW PROCESSLIST statement to view the current queries and identify any long-running queries.
  • Use the SHOW ENGINE INNODB STATUS statement: Use the SHOW ENGINE INNODB STATUS statement to view the InnoDB status and identify any performance issues.

Q&A: Troubleshooting and Resolving the Issue

In the previous article, we discussed the possible causes and solutions to resolve the issue of a hanging or slow query when retrieving statistics from the information_schema.STATISTICS table. In this article, we'll provide a Q&A section to help you troubleshoot and resolve this issue.

Q: What is the information_schema.STATISTICS table?

A: The information_schema.STATISTICS table is a system view in MySQL that provides information about the indexes and statistics of the tables in your database.

Q: Why is my query hanging or taking a long time to complete?

A: There are several possible causes of this issue, including:

  • Innodb_stats_on_metadata: This variable controls whether InnoDB collects statistics on metadata operations. If this variable is set to 1, InnoDB collects statistics on metadata operations, which can lead to performance issues when retrieving statistics from the information_schema.STATISTICS table.
  • Large number of tables or indexes: If your database has a large number of tables or indexes, retrieving statistics from the information_schema.STATISTICS table can be a time-consuming process.
  • Index corruption: Corrupted indexes can lead to performance issues when retrieving statistics from the information_schema.STATISTICS table.
  • Server load: High server load can cause performance issues when retrieving statistics from the information_schema.STATISTICS table.

Q: How can I resolve the issue of a hanging or slow query?

A: To resolve the issue of a hanging or slow query, you can try the following solutions:

1. Set innodb_stats_on_metadata to 0

As mentioned earlier, setting innodb_stats_on_metadata to 0 can resolve the issue of a hanging or slow query when retrieving statistics from the information_schema.STATISTICS table. To set this variable, you can use the following command:

SET GLOBAL innodb_stats_on_metadata = 0;

2. Optimize the query

If you're retrieving statistics from a large number of tables or indexes, you can optimize the query by using a WHERE clause to filter the results. For example:

SELECT *
FROM information_schema.STATISTICS
WHERE TABLE_NAME = 'your_table_name';

3. Check for index corruption

Corrupted indexes can lead to performance issues when retrieving statistics from the information_schema.STATISTICS table. To check for index corruption, you can use the following command:

CHECK TABLE your_table_name;

4. Reduce server load

High server load can cause performance issues when retrieving statistics from the information_schema.STATISTICS table. To reduce server load, you can try the following:

  • Close unnecessary connections: Close any unnecessary connections to the database to reduce the load on the server.
  • Optimize queries: Optimize any long-running queries to reduce the load on the server.
  • Add more resources: If the server is underpowered, consider adding more resources, such as CPU or memory, to improve performance.

Q: What are some additional tips to help me troubleshoot and resolve the issue?

A: Here are some additional tips to help you troubleshoot and resolve the issue of a hanging or slow query when retrieving statistics from the information_schema.STATISTICS table:

  • Use the EXPLAIN statement: Use the EXPLAIN statement to analyze the query plan and identify any performance issues.
  • Use the SHOW PROCESSLIST statement: Use the SHOW PROCESSLIST statement to view the current queries and identify any long-running queries.
  • Use the SHOW ENGINE INNODB STATUS statement: Use the SHOW ENGINE INNODB STATUS statement to view the InnoDB status and identify any performance issues.

Q: How can I prevent this issue from occurring in the future?

A: To prevent this issue from occurring in the future, you can try the following:

  • Regularly check and repair indexes: Regularly check and repair indexes to prevent corruption and improve performance.
  • Optimize queries: Optimize queries to reduce the load on the server and improve performance.
  • Monitor server load: Monitor server load to identify any performance issues and take corrective action.

By following these tips and solutions, you can resolve the issue of a hanging or slow query when retrieving statistics from the information_schema.STATISTICS table and improve the performance of your database.