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

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

From

michele curioni

Date:

24 February 2023, 00:18:20

Hi,

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

The sql update has a where clause on the primary key:

update table set status='a' where column_a = {value1} and column_b={value2}

The table's primary key is a composition of column_a and column_b

thread1 and thread2 use different values for value1 and value2

Does anyone have any idea how the problem could happen?

Thanks,

Michele

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

From

Tom Lane

Date:

24 February 2023, 01:10:56

michele curioni <mic.curioni@googlemail.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