KIP-989 — Improved StateStore Iterator metrics for detecting leaks

Accepted Kafka 3.8 StreamsMetrics

Adds num-open-iterators and thread-open-iterators metrics per StateStore in Kafka Streams to expose the count of currently open (potentially leaked) store iterators. Iterator leaks on RocksDB stores pin in-memory blocks and cause memory growth, but the existing block-cache-pinned-usage metric reports shared block cache usage without identifying which store is responsible.

Details