Error log flooded with "Unable to normalize query"

[maxxer]

Hi. My cloud MySQL instance is flooded with identical messages like the one below:

2024-03-04T10:18:23.973486Z 76108200 [Warning] [MY-000000] [Server] Unable to normalize query; Additional details available are Query Text: Database Name: mydb_prod Hostname: Username:

I'm puzzled because it doesn't report any detail, and I don't know how to investigate further to solve it.

Any hint is welcome. Thanks.

[ms4446]

The "Unable to normalize query" warning in MySQL signals a problem during query normalization—a step where MySQL simplifies a query for efficient planning, execution, and caching. Common causes include:

• Complex Query Structure: Overly elaborate queries with numerous subqueries, joins, nested expressions, or unusual syntax can hinder normalization.
• Outdated Statistics: MySQL relies on up-to-date table statistics (row counts, data distribution) to choose the best query plan. Inaccurate statistics can lead to normalization issues and poor performance.
• Database Design Issues: Suboptimal table designs, missing indexes, or inefficient data types can contribute to normalization difficulties.

Troubleshooting Steps

1. Pinpoint Problematic Queries:

   • Error Logs: Examine your MySQL error logs for the exact "Unable to normalize query" warnings. Correlate these warnings with timestamps to identify specific queries logged around those times.
   • Monitoring Tools: If you use database monitoring tools, they may capture queries associated with normalization warnings.

2. Enable Targeted Logging:

   • log_queries_not_using_indexes: Log queries that are not effectively using indexes. This helps pinpoint potential indexing problems.
   • Slow Query Log: Logs slow queries that often correlate with normalization issues. Enable it by setting the slow_query_log and slow_query_log_file variables or using the Cloud SQL console.

3. Analyze with EXPLAIN:

   • Run EXPLAIN on the identified problematic queries to dissect MySQL's execution plan. Pay attention to:
     • Table scans instead of index usage.
     • Excessive temporary tables or filesorts.

4. Update Table Statistics:

• Use ANALYZE TABLE to refresh statistics on relevant tables. This ensures MySQL has accurate information for optimization.

5. Optimize Queries and Indexing:
   • Query Refactoring: Consider simplifying the structure of complex queries, or breaking them down into smaller, more manageable ones.
   • Strategic Indexing: Create indexes on columns frequently involved in WHERE clauses, joins, or ORDER BY operations. Be mindful of index size and maintenance overhead.

Additional Tips

• Query Insights: Utilize Google Cloud SQL's Query Insights for deeper analysis of query performance patterns.
• MySQL Version: Stay updated with MySQL versions to leverage the latest performance improvements and bug fixes.
• Google Cloud Support: For persistent issues, don't hesitate to reach out to Google Cloud Support for expert assistance.

[maxxer]

Hi, thank you very much for the broad explaination.

Unfortunately, the error message doesn't give a hint on which query is triggering it. Also, the frequency on which the error is shown raises many questions for me. The error is printed every second or even more, and it's impossible we have complex queries so often.

Additionally, we have a staging environment that doesn't trigger the same error. There are none.

[ms4446]

Given the persistent and unclear nature of the issue, engaging Google Cloud Support might be your best next step. They can provide more in-depth analysis tools, access to logs not available  and the expertise to diagnose issues that are not easily identifiable from the surface.