[evgeny-simplex]

SMP server

• The notification store (NtfStore) uses StmContainers.Map instead of a TVar (Map ..). Sending clients write it per key at message rate, and the delivery thread inserts and deletes keys every delivery interval; with one map TVar these writes invalidated each other.
• Whole-store reads (delivery, expiration, saving, restore count, control port) read one entry per transaction (getNtfs), without a whole-map snapshot.
• Notifications of deleted queues are removed after delivery one notifier per transaction.
• Delivery batches and the saved notifications file list notifiers in hash order; notifications of each notifier keep their order.

Other maps

All 84 STM maps and sets were reviewed; the other 83 stay TVar containers: they are small, have a single main writer, or are snapshotted, sized or emptied as a whole on regular paths.

Dependencies

• stm-containers and list-t for the server build only (not with client_library); stm-containers for the tests.
• hashable moves to the common dependencies for the new Hashable EntityId instance.

[evgeny-simplex]

Closed: benchmarks show the TVar Map store is faster than stm-containers for this workload (1.2-2x higher store throughput; whole-store reads cost one transaction per entry instead of one readTVarIO).