From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
cc: Michael Paquier <michael.paquier@gmail.com>,
        Tomas Vondra <tomas.vondra@2ndquadrant.com>,
        PostgreSQL mailing lists <pgsql-hackers@postgresql.org>
Subject: Re: Re: PANIC: invalid index offnum: 186 when processing BRIN indexes
 in VACUUM
In-reply-to: <11499.1509476951@sss.pgh.pa.us>
References: <20171031181053.xh7hzminpv6rvwr2@alvherre.pgsql>
 <11499.1509476951@sss.pgh.pa.us>
Comments: In-reply-to Tom Lane <tgl@sss.pgh.pa.us>
	message dated "Tue, 31 Oct 2017 15:09:11 -0400"
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Date: Tue, 31 Oct 2017 15:46:32 -0400
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I wrote:
> maybe
> we just have some run-of-the-mill bugs to find, like the off-the-end
> bug I spotted in brin_doupdate.  There's apparently at least one
> more, but given the error message it must be something like not
> checking for a page to have turned into a revmap page.  Shouldn't
> be too hard to find...

Actually, I think it might be as simple as the attached.
brin_getinsertbuffer checks for the old page having turned into revmap,
but the "samepage" path in brin_doupdate does not :-(

With this applied, Alvaro's version of the test case has survived
without error for quite a bit longer than its former MTBF.  There
might still be some issues though in other code paths.

			regards, tom lane


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diff --git a/src/backend/access/brin/brin_pageops.c b/src/backend/access/br=
in/brin_pageops.c
index 80f803e..b0f86f3 100644
*** a/src/backend/access/brin/brin_pageops.c
--- b/src/backend/access/brin/brin_pageops.c
*************** brin_doupdate(Relation idxrel, BlockNumb
*** 113,121 ****
=20=20
  	/*
  	 * Check that the old tuple wasn't updated concurrently: it might have
! 	 * moved someplace else entirely ...
  	 */
! 	if (!ItemIdIsNormal(oldlp))
  	{
  		LockBuffer(oldbuf, BUFFER_LOCK_UNLOCK);
=20=20
--- 113,127 ----
=20=20
  	/*
  	 * Check that the old tuple wasn't updated concurrently: it might have
! 	 * moved someplace else entirely, and for that matter the whole page
! 	 * might've become a revmap page.  Note that in the first two cases
! 	 * checked here, the "oldlp" we just calculated is garbage; but
! 	 * PageGetItemId() is simple enough that it was safe to do that
! 	 * calculation anyway.
  	 */
! 	if (!BRIN_IS_REGULAR_PAGE(oldpage) ||
! 		oldoff > PageGetMaxOffsetNumber(oldpage) ||
! 		!ItemIdIsNormal(oldlp))
  	{
  		LockBuffer(oldbuf, BUFFER_LOCK_UNLOCK);
=20=20

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