SQL Server Replication Latency

Why this problem matters

Transactional replication latency can indicate that the distributor or subscriber cannot process changes at the production rate. Backlog and end-to-end delivery time may grow even while an agent appears to be running.

How to diagnose it

When tracer-token results exist, inspect publisher-to-distributor and distributor-to-subscriber times separately. Without that data, evaluate agent history, distributor backlog, and network or subscriber resources together.

The query reads existing tracer-token records from the distribution database and creates no new token. Adapt it if the distribution database has another name; no rows do not prove zero replication latency.

SELECT TOP (50)
       publication_id,
       publisher_commit,
       distributor_commit,
       subscriber_commit,
       DATEDIFF_BIG(millisecond, publisher_commit, distributor_commit) AS publisher_to_distributor_ms,
       DATEDIFF_BIG(millisecond, distributor_commit, subscriber_commit) AS distributor_to_subscriber_ms
FROM distribution.dbo.MStracer_tokens
WHERE publisher_commit IS NOT NULL
ORDER BY publisher_commit DESC;

A safe solution approach

After identifying the slow segment, investigate agent profile, distributor capacity, subscriber queries, and network issues in a targeted way. Reinitializing a subscription should not be the default response without understanding data volume and outage impact.

Why continuous monitoring matters

Latency can grow rapidly during write-heavy periods and disappear before a manual check. moon can monitor relevant SQL Server signals and route persistent-delay alerts through Slack, PagerDuty, or webhooks.