Stabilize Bespoke C++ Database

I have an in-house C++ data engine that talks to a MySQL front end. Under normal use it works, but once we start running real-world queries it can crash outright and, when it stays up, occasionally returns missing rows or pulls the wrong records altogether. These errors only appear while queries are executing; startup and idle periods are trouble-free.

Your task is to track down the causes of the query-time crashes, eliminate them, and tighten the code so the engine no longer drops or misreports data. I expect clean, well-commented fixes, unit or integration tests that prove stability against typical and edge-case queries, and a brief summary of what was wrong and how you corrected it. C++, MySQL, and solid debugging tools (gdb, Valgrind, sanitizers, etc.) will be essential.

Once the patches are in place and the tests pass locally, we’ll run the same suite on our staging server; payment releases after the engine survives those checks without crashing and consistently returns correct, complete result sets.