Ashutosh Bapat shares a tip with us:
Logical replication is a versatile feature offered in PostgreSQL. I have discussed the the theoretical background of this feature in detail in my POSETTE talk. At the end of the talk, I emphasize the need for monitoring logical replication setup. If you are using logical replication and have setup monitoring you will be familiar with pg_stat_replication_slots. In some cases this view shows high amount of spill_txns, spill_count and spill_bytes, which indicates that the WAL sender corresponding to that replication slot is using high amount of disk space. This increases load on the IO subsystem affecting the performance. It also means that there is less disk available for user data and regular transactions to operate. This is an indication that logical_decoding_work_mem has been configured too low. That’s the subject of this blog: how to decide the right configuration value for logical_decoding_work_mem. Let’s first discuss the purpose of this GUC. Blog might serve as a good background before reading further.
Read on to learn a bit more about how this value works and what you can do to set it correctly.