Re: assertion in 9.4 with wal_level=logical

On 2014-04-18 16:44:55 +0200, Robert Haas wrote:
> On Thu, Apr 17, 2014 at 10:47 PM, Andres Freund <andres@2ndquadrant.com> wrote:
> > On 2014-04-17 17:40:01 -0300, Alvaro Herrera wrote:
> >> For once, this looks more like a problem in logical decoding, which is
> >> trying to assert about the tuple being updated; the assertion failing is
> >> the one added a week ago about not palloc'ing in a critical section.
> >
> > It's this (older) assertion in HeapTupleHeaderGetCmax():
> >
> >         Assert(TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetUpdateXid(tup)));
> >
> > That can allocate memory if xmax is a multixact... Does anybody have a
> > better idea to solve this than adding a CritSectionCount == 0 && in
> > there?
> 
> Blech.  Isn't that just nerfing the assertion?

Not precicisely sure what you mean, but the only memory allocation in
HeapTupleHeaderGetCmax() and log_heap_new_cid() is that Assert(). And
that's the only "forbidden" thing in that codepath.
Now, we could alternatively restructure the codepaths so they pass in
xmax from outside the critical section, but I had a quick look and the
risk/complications from that seems bigger than the assertion buys us
there.
I don't have a better idea unfortunately :(

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services