Re: [HACKERS] [COMMITTERS] pgsql: Fix freezing of a dead HOT-updated tuple

On Thu, Dec 7, 2017 at 5:23 AM, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:
> Looking at 0002: I agree with the stuff being done here.

The level of details you are providing with a proper error code is an
improvement over the first version proposed in my opinion.

> I think a
> couple of these checks could be moved one block outerwards in term of
> scope; I don't see any reason why the check should not apply in that
> case. I didn't catch any place missing additional checks.

In FreezeMultiXactId() wouldn't it be better to issue an error as well
for this assertion?
Assert(!TransactionIdPrecedes(members[i].xid, cutoff_xid));

> Despite these being "shouldn't happen" conditions, I think we should
> turn these up all the way to ereports with an errcode and all, and also
> report the XIDs being complained about. No translation required,
> though. Other than those changes and minor copy editing a commit
> (attached), 0002 looks good to me.

+ if (!(tuple->t_infomask & HEAP_XMAX_LOCK_ONLY) &&
+ TransactionIdDidCommit(xid))
+ ereport(ERROR,
+ (errcode(ERRCODE_DATA_CORRUPTED),
+ errmsg("can't freeze committed xmax %u", xid)));
The usual wording used in errmsg is not the "can't" but "cannot".

+ ereport(ERROR,
+ (errcode(ERRCODE_DATA_CORRUPTED),
+ errmsg_internal("uncommitted Xmin %u from
before xid cutoff %u needs to be frozen",
+ xid, cutoff_xid)));
"Xmin" I have never seen, but "xmin" I did.

> I started thinking it'd be good to report block number whenever anything
> happened while scanning the relation. The best way to go about this
> seems to be to add an errcontext callback to lazy_scan_heap, so I attach
> a WIP untested patch to add that. (I'm not proposing this for
> back-patch for now, mostly because I don't have the time/energy to push
> for it right now.)

I would recommend to start a new thread and to add that patch to the
next commit fest as you would get more visibility and input from other
folks on -hackers. It looks like a good idea to me.
--
Michael