Problem with locks

Gregory Stark wrote:

I'm debugging this problem with stalled transactions waiting on locks which
have already been granted and I'm puzzled by something. What is this PGPROC
entry from?

It's not a real process (pid is 0) and it's not garbage either (prev and next
both point to a real PGPROC entry, namely MyProc which as you can see is
waiting for this PGPROC).

Doesn't this look like your pointer arithmetic being borked? There are
too many values that look invalid.

(gdb) p *(PGPROC*)(ShmemBase + MyProc->links.prev)
$2 = {links = {prev = 2520941752, next = 2520941752}, sem = {semId = 1, semNum = 0}, waitStatus = 0, xid = 0, xmin = 0, pid = 0,
databaseId = 0, roleId = 0, inCommit = 0 '\0', inVacuum = 0 '\0', isAutovacuum = 0 '\0', lwWaiting = 0 '\0', lwExclusive = 2 '\002',
lwWaitLink = 0x0, waitLock = 0x2, waitProcLock = 0x0, waitLockMode = 0, heldLocks = 0, myProcLocks = {{prev = 0, next = 1}, {
prev = 4294967296, next = 0}, {prev = 3028785127, next = 360654}, {prev = 73183493944770560, next = 137438953600}, {
prev = 2520929504, next = 2520929072}, {prev = 2520940536, next = 2520940536}, {prev = 1, next = 0}, {prev = 0,
next = 4294967296}, {prev = 4294967296, next = 0}, {prev = 2, next = 0}, {prev = 0, next = 0}, {prev = 1, next = 4294967296}, {
prev = 0, next = 4000475635}, {prev = 360707, next = 73183493944770560}, {prev = 128, next = 2520933680}, {prev = 2520933680,
next = 2520914616}}, subxids = {overflowed = -72 '�', nxids = 0, xids = {0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0,
0, 0, 1, 0, 0, 1, 0, 0, 1626942462, 0, 16384, 16430, 0, 16777216, 2, 0, 2520930944, 0, 2520930944, 0, 2520914784, 0, 2520914784,
0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0}}}
(gdb) p MyProc-ShmemBase
$3 = (PGPROC *) 0xff9ac36e36e264b8
(gdb) p (unsigned long)MyProc-ShmemBase
$4 = 2520941752

--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com

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Gregory Stark <stark@enterprisedb.com> writes:

I'm debugging this problem with stalled transactions waiting on locks which
have already been granted and I'm puzzled by something. What is this PGPROC
entry from?

I seem to recall that there's a dummy sentinel header in proc lists ...
is that what you're looking at?

regards, tom lane