Re: Could not serialize access due to read/write dependencies among transactions

michele curioni <mic(dot)curioni(at)googlemail(dot)com> writes:
> we have a Spring Boot application that tries to update two separate rows in
> a table in 2 separate threads, and it uses the default Transaction
> Isolation level of READ_COMMITTED.
> One of the two threads always succeeds, the other always fails with:

> org.postgresql.util.PSQLException: ERROR: could not serialize access
> due to read/write dependencies among transactions
> [java] ERROR> Detail: Reason code: Canceled on identification as a
> pivot, during write.
> [java] ERROR> Hint: The transaction might succeed if retried.

> I thought that error could only happen for SERIALIZABLE transactions,

Indeed. I think you're mistaken to claim that the transactions are
running in READ COMMITTED.

> moreover, the two threads are trying to update different rows.

That part's not so hard to explain: serializable mode's tracking of
which rows received updates is a bit lossy. It might be complaining
just because the updated rows were on the same page.

regards, tom lane