A possible reason for pg_wal buildup is that there is a sort of replication going on(logical or physical replication) and the receiving side of the replication has stopped somehow.
This means: a different server that has a connection to your server and is expecting to receive data. And your server is then expecting to have to send data(this is the important bit). There could be multiple of these connections.
If even 1 of these receiving servers is down, or the network is out, or there is some other reason that it is no longer requesting data from your server, your server will notice it isn't getting confirmation from that other side, that they have received the data. As such, your postgres server will keep this data locally, expecting this situation to be solved in the future, and at that point in time, send all the data the other side hasn't gotten yet.
This is 1 option. As long as your server is configured to expect that other server to be there, and to be receiving, the buildup will continue. Taking the other server offline won't help, in fact it is likely the cause of the issue. The official documentation explains how to get rid of replication slots, ideally your DBA should handle this.
Laurenz's blogpost lays out all the options, for instance it can also happen that your system is generating data so fast, the writing of the WAL files cannot keep up. Or your setup also does WAL archiving and the compression on that is slow.
The post offers some ways to verify things, I suggest checking them out.
And of course, if your DBA is back, have them look at it too.
Regards,
Koen De Groote
