Replication
ALTER TABLE ... REPLICA IDENTITY FULL
Lock mode ACCESS EXCLUSIVE
Risk HIGH
Blocks reads, writes, other DDL
pgfence rule
replica-identity-full ALTER TABLE orders REPLICA IDENTITY FULL;What this does
The ALTER itself is a brief metadata change, but the consequence is not: every UPDATE and DELETE now writes the entire old row image to WAL instead of just the key. That is a 10x to 100x amplification of WAL volume on the table, and it can saturate logical replication consumers like Debezium or pglogical. Almost always a misconfiguration.
Safe rewrite
Prefer the primary key (the default) or a specific unique non-null index instead of FULL
-- Prefer the primary key (the default if one exists)
ALTER TABLE orders REPLICA IDENTITY DEFAULT;
-- Or a specific unique non-null index
ALTER TABLE orders REPLICA IDENTITY USING INDEX orders_external_id_key_idx;