Hi- We have a master (pg 9.4.4 on Ubuntu 14.10) and a slave (pg 9.4.8 on Centos 7). During a period of heavy use, the slave began complaining that the “requested WAL segment xxxxxx has already been removed”. But the WAL segment was still on the master. The issue was resolved by manually copying the pg_xlog directory over to the slave.
I don’t see any errors on the master log file, or any other messages on the slave’s. What happened? How can this be prevented in the future?
If you are using streaming replication, then, enabling replication slots will ensure all the WALs which are not replayed to slave will be retained at master.
Having said that, your situation seems a bit strange to me. Slave cannot complain about an existing WAL segment at master, can you just give a bit more details about your replication architecture ?
Slave is unable to read the required WAL segment for some reason ? Do you have this situation happening regularly ?