Under the hood: MySQL Pool Scanner (MPS)

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Introduced MySQL Pool Scanner (MPS), a state machine system written in Python to automate routine MySQL DBA tasks for Meta's large-scale database clusters. MPS manages instance states (production, spare, drained, etc.) and uses 'problems' (tags) to drive automated actions like instance replacement and primary promotion, enabling bulk maintenance operations with minimal human intervention. It relies on a central repository for state management and integrates with Xtrabackup for data copying and Windex for reimaging.