Re: [sqlsmith] crashes in RestoreSnapshot on hot standby

On Fri, Jul 1, 2016 at 9:38 AM, Thomas Munro
<thomas(dot)munro(at)enterprisedb(dot)com> wrote:
> On Fri, Jul 1, 2016 at 3:25 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>> On Fri, Jul 1, 2016 at 8:48 AM, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>
>> wrote:
>>> If serialized_snapshot->xcnt == 0, then snapshot->xip never gets
>>> initialized to a non-NULL value. Then if serialized_snapshot->subxcnt
>>> > 0, we set snapshot->subxip = snapshot->xip +
>>> serialized_snapshot->xcnt (so that's NULL too). Then in line the line
>>> you show we call memcpy(snapshot->subxip, ...). The fix might be
>>> something like the attached.
>>
>> I was just typing the mail, when I see this mail. I also reached to the
>> conclusion that this is the reason of crash. You can see how CopySnapshot
>> calculates the subxipoff, may be writing code that way will be more
>> consistent.
>
> Or maybe just like this?
>
> - snapshot->subxip = snapshot->xip + serialized_snapshot->xcnt;
> + snapshot->subxip = ((TransactionId *) (snapshot + 1)) +
> + serialized_snapshot->xcnt;
>

This way it looks better to me. Thanks for the patch.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com