On Mon, Feb 28, 2011 at 6:38 PM, Robert Haas <robertmhaas@gmail.com> wrote:
>> Remember that it's not only about saving shared memory, it's also
>> about making sure that the snapshot reflects a state of the database
>> that has actually existed at some point in the past. Furthermore, we
>> can easily invalidate a snapshot that we have published earlier by
>> deleting its checksum in shared memory as soon as the original
>> transaction commits/aborts. And for these two a checksum seems to be a
>> good fit. Saving memory then comes as a benefit and makes all those
>> happy who don't want to argue about how many slots to reserve in
>> shared memory or don't want to have another GUC for what will probably
>> be a low-usage feature.
>
> But you can do all of this with files too, can't you? Just remove or
> truncate the file when the snapshot is no longer valid.
Sure we can, but it looked like the consensus of the first discussion
was that the through-the-client approach was more flexible. But then
again nobody is actively arguing for that anymore.
