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MySQL 8.0 Reference Manual  / ...  / Optimization  / Tracing the Optimizer  /  Tracing Memory Usage

10.15.5 Tracing Memory Usage

Each stored trace is a string, which is extended (usingrealloc()) as optimization progresses by appending more data to it. Theoptimizer_trace_max_mem_size server system variable sets a limit on the total amount of memory used by all traces currently being stored. If this limit is reached, the current trace is not extended, which means the trace is incomplete; in this case theMISSING_BYTES_BEYOND_MAX_MEM_SIZE column shows the number of bytes missing from the trace.