Announcing walctl for PostgreSQL Transaction Log Management
I’ve managed to convince my employer to open source one of the tools I recently wrote. That tool goes by the name of walctl, and I believe the importance of this kind of tool can not be overstated.
The PostgreSQL Write Ahead Log (WAL) files are key to crash recovery, point in time recovery, and all standby use not derived from streaming replication. WAL files are extremely critical to proper database operation. Yet their archival is treated as an afterthought. Some people use regular
cp while others go as far as to use
rsync to send data to a replica server.
This isn’t enough. A much safer architecture is to involve three servers. One server produces WAL files. One server acts as a storage and distribution location. One (or more) final server consumes the WAL files as necessary. In instances where streaming replication gets disconnected and the replica is too far behind for the WAL files the master server has available, the archive is a good mechanism for catching up.
Well, wallctl does all of that. It forces you to do all of that. Just set up a couple SSH keys prior to installation, and it needs nothing else. I added a database clone tool as a convenience which needs superuser access to the master database, but otherwise, walctl is very unobtrusive. This toolkit is simple, and will have a few limited advancements in updated versions. It’s meant to be small, fast, and light, following the UNIX philosophy of doing one thing well. In fact, I wrote this tool after examining several other PostgreSQL WAL and replication management systems. Almost all of them require transmitting WAL files directly from the master server to one or more slave systems. But this presumes you only have one replica, or forces the master server to do much more work by contacting several systems in a row. Why not let the slaves do all the hard work?
I highly recommend all DBAs use a WAL management tool of some kind, no matter which. Barman and repmgr are great alternatives that do much more than walctl. But if all you want to do is stash your WAL files in a safe location that multiple replica servers can utilize, this is the easier path.