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

Heikki Linnakangas  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