Foreign key relationships cause quadratic MultiXact member growth under concurrent writes

Foreign keys compound MultiXact member consumption. When multiple transactions insert rows referencing the same parent rows, PostgreSQL creates separate MultiXacts for each referenced row. With n backends share-locking a row, PostgreSQL creates O(n) MultiXacts and O(n^2) members (e.g., 5 transactions create 4 MultiXacts with 14 total members).

Audit foreign key usage, especially on low-cardinality enum tables. Consider removing or restructuring foreign keys on tables experiencing high concurrent insert volume. Monitor member space consumption during bulk insert operations. Evaluate moving high-write workloads off PostgreSQL if foreign key constraints are essential.