Migrate with Confidence—Scale Without Lock-In

-- 1. Inspect active replication slot lag and WAL retention limits
SELECT
  slot_name,
  plugin,
  active,
  pg_size_pretty(pg_wal_lsn_diff(pg_current_wal_lsn(), confirmed_flush_lsn)) AS replication_lag_bytes,
  wal_status
FROM pg_replication_slots
WHERE slot_type = 'logical';

-- 2. Measure write latency and subscriber connection state
SELECT application_name, client_addr, state, sync_state,
       round(extract(epoch from (now() - reply_time))::numeric, 2) AS seconds_since_last_msg
FROM pg_stat_replication;

-- 1. PostgreSQL row-level MD5 block hash validation
SELECT
  count(*) AS row_count,
  md5(string_agg(id::text || ':' || updated_at::text, ',' ORDER BY id)) AS table_checksum
FROM account_transactions
WHERE created_at >= '2026-01-01' AND created_at < '2026-02-01';

-- 2. Verify target sequence synchronization after cutover
SELECT c.relname, s.last_value, s.is_called
FROM pg_sequences s
JOIN pg_class c ON c.relname = s.sequencename;