performance tuning

Everyone says 'add an index,' but a strong engineer reads the plan first. The signal is finding the dominant operator, comparing estimated vs actual rows, and recognizing the seq-scan, bad-join, and spill patterns.

Partition on the wrong key and you get millions of tiny files or skewed giants. The signal is partitioning on a low-cardinality filter, clustering within partitions on the next predicate, and watching file size.