On 11/30/2011 09:19 PM, Nicholson, Brad (Toronto, ON, CA) wrote:
This functionality is something that Postgres can do today. We expose
the ability to do this with explicit savepoints. The difference is
that Oracle allows you to set it on a per transaction basis (I
believe) and it will behave this way for all statements in the
transaction, where as we need to do it explicitly. Looking through the
archives there does seem to be a performance problem on commit in
Postgres if you issue a lot of savepoints (there were discussions of a
fix but I am not sure the status of this).
Savepoint performance has had several improvements over time. Back in
8.1 when I got started developing against Pg seriously I was having
*MASSIVE* performance issues with PL/PgSQL exception blocks (which use
savepoints) in loops; these days it's perfect.
To make automatic savepoints viable, Pg would need to be able to
completely forget a savepoint once it's been released, so there's no
ongoing cost. That way a transaction would only need two savepoints at
any particular point in time. My understanding is that it's not there
yet; AFAIK released savepoints still have a non-trivial cost that would
add up if someone was using automatic savepoints in (say) a 10,000
INSERT transaction.
--
Craig Ringer
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