Re: SELECT blocks UPDATE

On 08/13/2015 02:14 PM, twoflower wrote:
> Further observation: Now I managed to get rid of the blocking. I am not sure
> if you are familiar with the NHibernate ORM, but it has a concept of a
> stateful and stateless sessions. Session holds a connection to the database
> and transaction is created on a particular session. In this case, 'begin
> transaction' and the SELECT statement was executed in the context of the
> stateful session, while the UPDATE was executed on a stateless session. I am
> not sure how this situation manifests on Postgres but since the 'blocked'
> and 'blocking' lock apparently belong to the same transaction, it does not
> look like it should matter, except it does.

I would crank up the Postgres logging:

http://www.postgresql.org/docs/9.4/interactive/runtime-config-logging.html#RUNTIME-CONFIG-LOGGING-WHAT

At least set log_statement to all, to see what is actually being sent to
the server from the ORM during the above.

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--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com