Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> wrote:
> On Wed, Dec 21, 2011 at 10:50 AM, Rafael Martinez
> <r(dot)m(dot)guerrero(at)usit(dot)uio(dot)no> wrote:
>> As long as I know, all the databases are using the default, "read
>> committed".
>
> Note that backups run in serializable mode.
In 9.1 they default to running in "repeatable read". You can choose
the --serializable-deferrable option, which runs at the serializable
transaction isolation level, sort of. It does that by waiting for a
"safe" snapshot and then running the same as a repeatable read
transaction -- so either way you have none of the overhead of the
new serializable transactions.
Besides that, almost all of the additional RAM usage for the new
serializable implementation is in shared memory. As you can see in
the graphs from Rafael, the difference isn't very dramatic as a
percentage of a typical production configuration.
-Kevin