btreemapped

to explain:

• postgres wal_sender_timeout and its interaction with tcp idle keepalive
• pitfalls of logical replication lagging, monitoring and recovery
• https://wolfman.dev/posts/pg-logical-heartbeats/
• BTreeWrite and the concept of postgres-as-kv-store

todo:

• String -> Cow conversions
• Erase arity from the type somehow?
• Pretty sure arity >= 2 iteration needs an additional bounds check
• Use fully qualified name for LIndex* in btreemapped_derive, so users don't have to import it explicitly

Check WAL growth and replication status

SELECT 
    slot_name,
    confirmed_flush_lsn, 
    pg_current_wal_lsn(), 
    (pg_current_wal_lsn() - confirmed_flush_lsn) AS lsn_distance
FROM 
    pg_replication_slots;