Re: Statement-level rollback

Tsunakawa> PgJDBC has supported the feature with autosave parameter only
recently

PgJDBC has the implementation for more than a year (REL9.4.1210,
2016-09-07, see https://github.com/pgjdbc/pgjdbc/pull/477 )

Tsunakawa> The point raised in this thread was that that creates
Tsunakawa> too much network overhead, so a backend-based solution would be
preferable.
Tsunakawa> We haven't seen any numbers or other evidence to quantify that
claim, so
Tsunakawa> maybe it's worth looking into that some more

The performance overhead for "SELECT" statement (no columns, just select)
statement over localhost is 36±4 us vs 38±3 us (savepoint is pipelined
along with user-provided query). That is network overhead is close to
negligible.

As far as I understand, the main problem with savepoints is they would
consume memory even in case the same savepoint is reassigned again and
again.
In other words, "savepoint; insert;savepoint; insert;savepoint;
insert;savepoint; insert;savepoint; insert;" would allocate xids and might
blow up backend's memory.
I see no way driver can workaround that, so it would be great if backend
could release memory or provide a way to do so.

Adding protocol messages would blow pgbouncer, etc things, so it makes
sense to refrain from new messages unless it is absolutely required.

Vladimir