Re: Snapshot synchronization, again...

On 22.02.2011 16:29, Robert Haas wrote:
> On Tue, Feb 22, 2011 at 8:58 AM, Heikki Linnakangas
> <heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
>> On 22.02.2011 15:52, Robert Haas wrote:
>>>
>>> On Tue, Feb 22, 2011 at 8:01 AM, Heikki Linnakangas
>>> <heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
>>>>
>>>> Yes. It would be good to perform those sanity checks anyway.
>>>
>>> I don't think it's good; I think it's absolutely necessary. Otherwise
>>> someone can generate arbitrary garbage, hash it, and feed it to us.
>>> No?
>>
>> No, the hash is stored in shared memory. The hash of the garbage has to
>> match.
>
> Oh. Well that's really silly. At that point you might as well just
> store the snapshot and an integer identifier in shared memory, right?

Yes, that's the point I was trying to make. I believe the idea of a hash
was that it takes less memory than storing the whole snapshot (and more
importantly, a fixed amount of memory per snapshot). But I'm not
convinced either that dealing with a hash is any less troublesome.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com