MySQL Memory Monitoring Improvements in InnoDB 8.0.28

In MySQL 8.0.28, InnoDB introduced a new memory monitoring system called PFS (Performance Schema) metadata to replace the older method of wrapping malloc() and free(). The new system uses a unified metadata structure to track memory allocations and deallocations, improving accuracy and supporting modern C++ features.

The key components include:

memory_summary_by_account_by_event_name : Tracks memory from user and host perspectives.

memory_summary_by_host_by_event_name : Host-level memory tracking.

memory_summary_by_thread_by_event_name : Thread-level memory tracking.

memory_summary_by_user_by_event_name : User-level memory tracking.

memory_summary_global_by_event_name : Global memory tracking per event.

Each table provides columns like COUNT_ALLOC, SUM_NUMBER_OF_BYTES_ALLOC, CURRENT_COUNT_USED, and LOW_NUMBER_OF_BYTES_USED to analyze memory usage.

The new allocator uses a metadata structure embedded in allocated memory blocks, allowing precise tracking without modifying existing code. This supports modern C++ features and reduces coupling with Performance Schema.

An example shows how the allocator works, including the use of ut_new_pfx_t to store metadata and the allocate_trace and deallocate_trace functions for memory tracking.

The refactoring addresses limitations of the old method, such as lack of support for STL containers and modern C++ syntax, and improves extensibility by using a base allocator trait.

A case study demonstrates how this system helped diagnose a user's OOM issue caused by a memory leak in a stored procedure's variable history tracking.