How do i measure redis replication delay?

Question

Which of these can be considered to monitor replication delay ? Redis_master_repl_offset, Redis_master_last_io_seconds_ago , Redis_slave_repl_offset

Solution

Given results from an INFO replication command like this:

slave0:172.16.101.23,6380,online,424821
master_repl_offset:424827

You can tell that slave0 is behind master by 6. This is the difference between the master_repl_offset and the offset value in the slave0 line, which is the last number in it. If you have multiple slaves, each will get their own line with their own offset value.

Comments

[karan sindwani]

What does value indicate ? What can be the threshold of a warning value ?

[Deb]

@karansindwani I believe the value there is bytes. I used small numbers here as an example, real ones would likely be very large. On our logstash redis instance, 1MB is a sign of pressure worthy of notice, but on an application-stack redis, even 20KB is considered slow. It depends, and only you can know what bad looks like.

[radtek]

For me the output looks like this slave0:ip=10.0.1.162,port=6379,state=online,offset=925994074‌​541,lag=0 so I'm looking at offset?

[Deb]

@radtek Yes, offset.