Re: BUG #5989: Assertion failure on UPDATE of big value

Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> wrote:
> On 20.04.2011 17:26, Tom Lane wrote:

>> Why is predicate.c getting called at all when
>> transaction_isolation is not SERIALIZABLE?  (Although the same
>> crash happens when it is ...)
>
> Because another serializable transaction that reads/updates the
> tuple later needs to find the predicate lock acquired by the
> first transaction, even if the transaction in the middle isn't
> serializable.

For an example of the issue, see this post:

http://archives.postgresql.org/pgsql-hackers/2011-02/msg00325.php

While all transactions there are serializable, the issue exists even
if the transaction which updates the tuple with the predicate lock
isn't serializable.

-Kevin