Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> wrote:
> Simon Riggs wrote:
>> It wouldn't be 692 lines of code and even if it were the impact of
>> that code would be such that it would need to be optional, since it
>> would differ in definition from an existing SQL Standard isolation
>> mode and it would have additional performance implications.
>
> I thought it would be equal to the SQL standard Serializable mode,
> whereas what we currently call serializable is in fact not as strong
> as the SQL standard Serializable mode.
Exactly. The standard probably *should* add SNAPSHOT between
REPEATABLE READ and SERIALIZABLE, but so far have not. As of the 2003
version of the SQL spec, they added explicit language that makes it
clear that what you get when you ask for SERIALIZABLE mode in
PostgreSQL is *not* compliant (although it is more than adequate for
REPEATABLE READ).
By the way, the other modes are all optional, as you're allowed to
escalate to a higher level whenever a lower level is requested;
SERIALIZABLE is required by the standard and is specified as the
default.
-Kevin