heap_update() currently ends with

    if (newbuf != buffer)
    {
        LockBuffer(newbuf, BUFFER_LOCK_UNLOCK);
        WriteBuffer(newbuf);
    }
    LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
    WriteBuffer(buffer);

    /* invalidate caches */
    RelationInvalidateHeapTuple(relation, &oldtup);
    RelationMark4RollbackHeapTuple(relation, newtup);

    return HeapTupleMayBeUpdated;

This is broken because WriteBuffer releases our refcounts on the buffer
pages that are holding the old and new tuples.  By the time
RelationInvalidateHeapTuple gets to do its thing, some other backend may
have swapped a new disk page into the shared buffer that oldtup points
at.  catcache.c will then be using the wrong data to compute the hash
index of the old tuple.  This will at minimum result in failure to
invalidate the old tuple out of our catcache (because we'll be searching
the wrong hashchains), and can lead to a flat-out crash or Assert
failure due to invalid data being fed to the hashing code.

I have seen several nonrepeatable failures in the parallel regress tests
in recent weeks, which I now believe are all traceable to this error.

I will commit a fix for this error shortly, and have recommended to Marc
that he re-roll the beta2 tarball before announcing it...

			regards, tom lane

Sun, 07 Jan 2001 16:38:25 -0500
Tom Lane <tgl@sss.pgh.pa.us>
heap_update is broken in current sources

How are we on this?

On Sun, 7 Jan 2001, Tom Lane wrote:

> heap_update() currently ends with
>
>     if (newbuf != buffer)
>     {
>         LockBuffer(newbuf, BUFFER_LOCK_UNLOCK);
>         WriteBuffer(newbuf);
>     }
>     LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
>     WriteBuffer(buffer);
>
>     /* invalidate caches */
>     RelationInvalidateHeapTuple(relation, &oldtup);
>     RelationMark4RollbackHeapTuple(relation, newtup);
>
>     return HeapTupleMayBeUpdated;
>
> This is broken because WriteBuffer releases our refcounts on the buffer
> pages that are holding the old and new tuples.  By the time
> RelationInvalidateHeapTuple gets to do its thing, some other backend may
> have swapped a new disk page into the shared buffer that oldtup points
> at.  catcache.c will then be using the wrong data to compute the hash
> index of the old tuple.  This will at minimum result in failure to
> invalidate the old tuple out of our catcache (because we'll be searching
> the wrong hashchains), and can lead to a flat-out crash or Assert
> failure due to invalid data being fed to the hashing code.
>
> I have seen several nonrepeatable failures in the parallel regress tests
> in recent weeks, which I now believe are all traceable to this error.
>
> I will commit a fix for this error shortly, and have recommended to Marc
> that he re-roll the beta2 tarball before announcing it...
>
> 			regards, tom lane
>

Marc G. Fournier                   ICQ#7615664               IRC Nick: Scrappy
Systems Administrator @ hub.org
primary: scrappy@hub.org           secondary: scrappy@{freebsd|postgresql}.org


Mon, 8 Jan 2001 10:28:18 -0400 (AST)
The Hermit Hacker <scrappy@hub.org>
Re: heap_update is broken in current sources
The Hermit Hacker <scrappy@hub.org> writes:
> How are we on this?

It's fixed.

I've also run the regress tests with bufmgr.c hacked up to discard
pages (with forcible overwriting) as soon as their refcount goes to
zero.  That didn't disclose any similar bugs, although the coverage
of the tests leaves much to be desired :-(

			regards, tom lane

Mon, 08 Jan 2001 10:26:36 -0500
Tom Lane <tgl@sss.pgh.pa.us>
Re: heap_update is broken in current sources 

okay, will bundle up beta2 and announce it tonight when I get home ...
gives about 6 hrs or so to "halt the presses" *grin*

On Mon, 8 Jan 2001, Tom Lane wrote:

> The Hermit Hacker <scrappy@hub.org> writes:
> > How are we on this?
>
> It's fixed.
>
> I've also run the regress tests with bufmgr.c hacked up to discard
> pages (with forcible overwriting) as soon as their refcount goes to
> zero.  That didn't disclose any similar bugs, although the coverage
> of the tests leaves much to be desired :-(
>
> 			regards, tom lane
>

Marc G. Fournier                   ICQ#7615664               IRC Nick: Scrappy
Systems Administrator @ hub.org
primary: scrappy@hub.org           secondary: scrappy@{freebsd|postgresql}.org


Mon, 8 Jan 2001 11:55:10 -0400 (AST)
The Hermit Hacker <scrappy@hub.org>
Re: heap_update is broken in current sources 