From: Antonin Houska <ah@cybertec.at>
To: pgsql-hackers@postgresql.org
Subject: Possibly too stringent Assert() in b-tree code
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Date: Mon, 19 Sep 2016 10:02:38 +0200
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I've recently seen this when using 9.6:

#0  0x00007f147892f0c7 in raise () from /lib64/libc.so.6
#1  0x00007f1478930478 in abort () from /lib64/libc.so.6
#2  0x00000000009683a1 in ExceptionalCondition (conditionName=3D0x9f2ef8 "!=
(((PageHeader) (page))->pd_special >=3D (__builtin_offsetof (PageHeaderData=
, pd_linp)))", errorType=3D0x9f2e8a "FailedAssertion",
    fileName=3D0x9f2e60 "../../../../src/include/storage/bufpage.h", lineNu=
mber=3D314) at assert.c:54
#3  0x00000000004ee3d2 in PageValidateSpecialPointer (page=3D0x7f14700f3480=
 "") at ../../../../src/include/storage/bufpage.h:314
#4  0x00000000004ef913 in _bt_getbuf (rel=3D0x7f14795a1a50, blkno=3D11, acc=
ess=3D2) at nbtpage.c:629
#5  0x00000000004eae8c in _bt_split (rel=3D0x7f14795a1a50, buf=3D136, cbuf=
=3D0, firstright=3D367, newitemoff=3D408, newitemsz=3D16, newitem=3D0x26083=
30, newitemonleft=3D0 '\000') at nbtinsert.c:986
#6  0x00000000004ea563 in _bt_insertonpg (rel=3D0x7f14795a1a50, buf=3D136, =
cbuf=3D0, stack=3D0x26090c8, itup=3D0x2608330, newitemoff=3D408, split_only=
_page=3D0 '\000') at nbtinsert.c:781
#7  0x00000000004e954c in _bt_doinsert (rel=3D0x7f14795a1a50, itup=3D0x2608=
330, checkUnique=3DUNIQUE_CHECK_YES, heapRel=3D0x25aa0a0) at nbtinsert.c:204
#8  0x00000000004f3b73 in btinsert (rel=3D0x7f14795a1a50, values=3D0x7ffe46=
c6f7f0, isnull=3D0x7ffe46c6f7d0 "", ht_ctid=3D0x260927c, heapRel=3D0x25aa0a=
0, checkUnique=3DUNIQUE_CHECK_YES) at nbtree.c:279
#9  0x00000000004e7964 in index_insert (indexRelation=3D0x7f14795a1a50, val=
ues=3D0x7ffe46c6f7f0, isnull=3D0x7ffe46c6f7d0 "", heap_t_ctid=3D0x260927c, =
heapRelation=3D0x25aa0a0, checkUnique=3DUNIQUE_CHECK_YES)
    at indexam.c:204

Of course, the database could have been corrupted after having encountered
many crashes during my experiments. Neverthelesss, even without in-depth
knowledge of the b-tree code I suspect that this stack trace might reflect a
legal situation. In partcular, if _bt_page_recyclable() returned on this
condition:

	if (PageIsNew(page))
		return true;


Unfortunately I no longer have the cluster nor the core dump, but I remember
all the fields of PageHeader were indeed zeroed.

--=20
Antonin Houska
Cybertec Sch=C3=B6nig & Sch=C3=B6nig GmbH
Gr=C3=B6hrm=C3=BChlgasse 26
A-2700 Wiener Neustadt
Web: http://www.postgresql-support.de, http://www.cybertec.at


--=20
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