You could very well be right.
We are using JPA under Hibernate, using container managed transactions. So T1 and T2 above are actually container managed transactions, each running in response to REST API requests. They should be bound 1:1 with underlying PostgreSQL transactions, but perhaps there is some asynchronous going on inside of Hibernate…
It’s off topic for this forum, but if anyone happens to know if JPA/Hibernate could be the culprit here, please let me know.
On Wed, Sep 24, 2014 at 2:01 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
"Steve Dodd" <steve@streetcontxt.com> writes:
> Say we have two transactions run sequentially: T1 writes some data, and T2 reads the written data. There is a non-zero time delay between the apparent T1 commit, and the subsequent T2 query.
> Is there any guarantee that the data written in T1 will be visible to the query in T2?
> We have a situation in our system where it would appear that the answer is NO.
Extremely hard to believe. There is a very well-defined point where the
transaction's effects become visible to other transactions, and that is
certainly before the commit is reported as complete to the client.
I suspect if you dig into it you'll find that your client-side code
is doing something unexpected.
Also worth checking is that "T2" is actually a transaction, and not
a single statement within a serializable-mode transaction. In the latter
case it would see the database state as of the transaction's snapshot,
which might precede T1's commit.
regards, tom lane
