| Type: | enum |
| Default: | replica |
| Context: | postmaster |
| Restart: | true |
| Values: | [minimal, replica, logical] |
wal_level determines how much information is written to the WAL. The default value is replica, which writes enough data to support WAL archiving and replication, including running read-only queries on a standby server. minimal removes all logging except the information required to recover from a crash or immediate shutdown. Finally, logical adds information necessary to support logical decoding. Each level includes the information logged at all lower levels. This parameter can only be set at server start.
The minimal level generates the least WAL volume. It logs no row information for permanent relations in transactions that create or rewrite them. This can make operations much faster (see populate-pitr). Operations that initiate this optimization include:
- ALTER ... SET TABLESPACE
- CLUSTER
- CREATE TABLE
- REFRESH MATERIALIZED VIEW (without CONCURRENTLY)
- REINDEX
- TRUNCATE
replica or higher must be used to enable continuous archiving (archive_mode) and streaming binary replication. In fact, the server will not even start in this mode if max_wal_senders is non-zero. Note that changing wal_level to minimal makes previous base backups unusable for point-in-time recovery and standby servers.
In logical level, the same information is logged as with replica, plus information needed to extract logical change sets from the WAL. Using a level of logical will increase the WAL volume, particularly if many tables are configured for REPLICA IDENTITY FULL and many UPDATE and DELETE statements are executed.
In releases prior to 9.6, this parameter also allowed the values archive and hot_standby. These are still accepted but mapped to replica.