Replication is the process that transfers data from an active master to a slave server, which reproduces the data stream to achieve, as best as possible, a faithful copy of the data in the master.
To check replication health, you may start with sampling the service, i.e. committing some Sentinel value in the master and retrieving it from the slave.
Sentinel data: Tap tap… Is this thing on?
If you want to make sure that replication is working, the easiest test is using replication itself to see if data is being copied across from the master to the slaves. The method is easy:
- Make sure that the data you want to see is NOT in the master or in the slave. If you skip this step, you may think that replication is working, while in fact it may not.
- Either create a table in the master or use a table that you know exists both in the master and the slave.
- Insert several records in the master table.
- Check that they are replicated in the slave correctly.
- Update a record in the master.
- Watch it changing in the slave.
- Delete a record in the master.
- Watch it disappear in the slave.