Re: [sqlsmith] crashes in RestoreSnapshot on hot standby

On Fri, Jul 1, 2016 at 8:48 AM, Thomas Munro <thomas.munro@enterprisedb.com> wrote:
>
> On Fri, Jul 1, 2016 at 2:17 PM, Michael Paquier
> <michael.paquier@gmail.com> wrote:
> > On Fri, Jul 1, 2016 at 6:26 AM, Andreas Seltenreich <seltenreich@gmx.de> wrote:
> >> #1  0x0000000000822032 in RestoreSnapshot (start_address=start_address@entry=0x7f2701d5a110 <error: Cannot access memory at address 0x7f2701d5a110>) at snapmgr.c:2020
> >
> >         memcpy(snapshot->subxip, serialized_xids + serialized_snapshot->xcnt,
> >                serialized_snapshot->subxcnt * sizeof(TransactionId));
> > So this is choking here? Is one of those pointers NULL?
>
> Theory 1:
> 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.
>

GetSnapshotData()
{
/*
* We're in hot standby, so get XIDs from KnownAssignedXids. --