Can PostgreSQL UPDATEs in autocommit mode deadlock?

Question

Is it possible for UPDATEs in PostgreSQL to deadlock when in autocommit mode? If so, how, and why? (Or, why not?)

Answer 1

That is certainly possible if the update affects more than a single table row.

This can come to pass in two ways:

• The query modifies more than a single row in the target table.

• The updated table has a foreign key constraint to another table. In that case, you may end up with a FOR KEY SHARE lock on the referenced table.

The deadlock can happen if your statement successfully locks a couple of rows and then blocks on a lock on some other row.