> xof@thebuild.com wrote:
>
>> bryn@yugabyte.com wrote:
>>
>> 2. If I send over "begin" and then "insert into s.t(v) values(42)", then (so far) a second session will not see the
effectof my SQL's. It sees this only when I send over "commit". (If I send over "rollback" instead of "commit", then
othersessions never know what I did.)
>
> This may or may not be true. If the second session currently has a transaction open in REPEATABLE READ or
SERIALIZABLEmode, it *won't* see the effects of that statement, since it took its snapshot at the start of the
transaction(to be technical, at the first statement in that transaction), and holds it until commit time. However, a
transactionin READ COMMITTED mode *will* see the results after the statement completes.
>
>> I can't see that a client-side "autocommit off" mode like psql supports brings me anything of value.
>
> There's general agreement on that point.
>
> https://www.cybertec-postgresql.com/en/disabling-autocommit-in-postgresql-can-damage-your-health/
Thanks, Christophe. Yes, I sacrificed correctness for brevity. I should have stipulated that observations made from a
secondconcurrent session are to be done using a singleton "select" in its own txn—i.e. outside of an explicitly started
txn(whether this is started by hand or using a client's implementation of "autocommit off"). Thanks, too, for the xref
tothe Cybertec post by Laurenz Albe.
And thanks, David, for your separate tip about using « psql -c ». I tried it and watched the server log. Sure enough, I
sawthis:
2023-02-20 12:42:44.993 PST [2540504] d0$u0@d0 LOG: 00000: statement: insert into s.t(v) values(17); insert into
s.t(v)values(42);
2023-02-20 12:42:44.993 PST [2540504] d0$u0@d0 LOCATION: exec_simple_query, postgres.c:971
It seems a bit odd that psql has no syntax to ask for this in its interactive mode. But, yes, it doesn't actually
matterbecause I can get the same semantics by starting a txn myself.
