- AWS – Lambda: Handlers, Cold Starts and Packaging
The handler signature, what actually lives in the execution context between invocations, and why that one fact decides where you open a database connection. Cold starts measured rather than feared, memory as the CPU dial it really is, layers versus a zip versus a container image, and the packaging trap that ships a Lambda which dies at import: compiled wheels built for your laptop instead of for Lambda.
- LeetCode 121 – Best Time to Buy and Sell Stock
Worth more than its Easy tag, because the reframing it teaches is the one behind Kadane's algorithm and most 1-D DP. The brute force asks which pair of days is best; the linear solution asks what the best buy was if I sell today — and that has a one-variable answer. Why a falling market returns 0, and why this is Maximum Subarray in disguise.
- MySQL – INFORMATION_SCHEMA
Querying the database about itself. TABLES, COLUMNS, STATISTICS, KEY_COLUMN_USAGE and REFERENTIAL_CONSTRAINTS, finding every foreign key pointing at a table before you drop it, listing indexes that duplicate each other, estimating table and index size on disk, why TABLE_ROWS is an estimate and not a count, and how SHOW commands map onto the same data.
- LeetCode 119 – Pascal's Triangle II
One row, in O(k) space, which turns a warm-up into a real exercise in updating an array without destroying what you are about to read. Sweep right to left so the stale values survive — the same rule that separates 0/1 knapsack from unbounded, and the question is always which values the cell needs.
- MySQL – Scheduled Events
Cron inside the database. The event_scheduler variable that is OFF by default so your first event never runs, CREATE EVENT with AT and with EVERY, STARTS and ENDS, ON COMPLETION PRESERVE, altering and disabling one, where errors go, what happens on a replica, and the question to settle first — whether this belongs in the database at all or in the scheduler you already operate.