How to find replication lag in SQL Server? - sql-server

Question

In MYSQL server by looking into the value for "second behind master" it can be known by how much a slave server is lagging behind to its master. So, is there something similar to it in MSSQL so that it can be known how a slave server is lagging behind by its master?

Answer 1

There is some controversy on this subject, but I like to use regularly posted tracer tokens. That is, you call the sp_posttracertoken procedure on the publisher and it will send a, well, token all the way through to the subscriber. You can see the history of all tokens in the distributor database. I wrote the following view to make the data a little easier to grok:
create view [dbo].[tokens] as
select
ps.name as [publisher],
p.publisher_db,
p.publication,
ss.name as [subscriber],
da.subscriber_db,
t.publisher_commit,
t.distributor_commit,
h.subscriber_commit,
datediff(second, t.publisher_commit, t.distributor_commit) as [pub to dist (s)],
datediff(second, t.distributor_commit ,h.subscriber_commit) as [dist to sub (s)],
datediff(second, t.publisher_commit, h.subscriber_commit) as [total latency (s)]
from mstracer_tokens t
inner join MStracer_history h
on t.tracer_id = h.parent_tracer_id
inner join mspublications p
on p.publication_id = t.publication_id
inner join sys.servers ps
on p.publisher_id = ps.server_id
inner join msdistribution_agents da
on h.agent_id = da.id
inner join sys.servers ss
on da.subscriber_id = ss.server_id
Another approach is to use what's commonly called a canary table. The idea is that you have a table specifically to monitor replication that typically only has one row with a datetime field. You update the column at the publisher and then you monitor how far behind the subscriber is by seeing what the value of that column is at the subscriber.
Lastly, there are some perfmon counters that you can look at. In my experience, they're not that great; the number of outstanding commands is an accurate number, but the measurement of latency as a duration is typically very inaccurate.