PostgreSQL Expands MultiXactOffset to 64 Bits, Eliminating Key Transaction Limit

PostgreSQL developer Heikki Linnakangas committed a patch widening the MultiXactOffset counter from 32 to 64 bits, effectively removing the previous cap of roughly 4 billion multitransaction members. The change eliminates MultiXactOffset wraparound, a condition that could previously force disruptive anti-wraparound vacuum operations on busy databases. Multitransactions are used internally by PostgreSQL whenever multiple transactions lock the same row, such as during SELECT FOR SHARE, FOR UPDATE operations, or foreign key enforcement. The patch author, who contributed directly to this work, notes that the new 64-bit limit is so large it is unlikely to be exhausted in any practical scenario. The commit has remained stable for nearly three months, signalling its acceptance into the PostgreSQL codebase.