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Re: Snapshot synchronization, again...

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Joachim Wieland <joe(at)mcknight(dot)de>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Noah Misch <noah(at)leadboat(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Snapshot synchronization, again...
Date: 2011-02-22 14:34:34
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
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

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