>> I currently have wal_keep_segments set to 0. >> Setting this to higher value will help? As I understand: master won't >> delete segment and could stream it to slave on request - so it will >> help. > > > It definitely helps, but the issue could still happen. >
What conditions must be met for issue to happen?
Very high WAL traffic can make the slave lag enough that even wal_keep_segments isn't enough.
Both archive_command on master and restore_commands are set and working. Also wal_keep_segments is set.
I see no point of failure - only delay in the case of high WAL traffic on master: - slave starts with restoring WALs from archive, - now, it connects to master and notices, that for last master's WAL it needs previous one ("the issue"), - slave asks master for previous WAL and gets it - job done, streaming replication set, exit - if unable to get it (WAL traffic is high, and after restoring last WAL from archive and asking master for next one more than wal_keep_segments were recycled) it returns to looking WALs in archive.
Do I get it right?
Yes. If you set correctly archive_command (on the master) and restore_command (on the slave), there's no point of failure. You might still get the "WAL not available" error message, but the slave can synchronize itself with the archived WALs.
