Reseting undo/redo logs

I have this issue on Greenplum which is a MPP hybrid build from
postgres 8.2, and the issue I am seeing is 100% from pg code.

One of the Greenplum segments went down and it cannot recover because
"PANIC    XX000 invalid redo/undo record in shutdown checkpoint
(xlog.c:6576)"

I am posting this question here because most casual users of
Postgres/Greenplum are telling me that database is hosed, but I think
that with pg_resetxlog and some
(http://www.postgresql.org/docs/8.2/static/app-pgresetxlog.html) data
loss I could at least "hack" database to come back up.

What I am asking for help here is to help me calculate the reset
values - where to find the most recent valid one and how to
*specifically* calculate the reset ones.

Please advise,
Edmon


2012-06-12 13:16:18.614912
EDT            p14611    th802662304                0            seg-1                    LOG    0    mirror
transition,
primary address(port) 'boxgp10a(41001)' mirror address(port)
'boxgp02a(51001)'                    mirroring role 'primary role' mirroring state
'change tracking' segment state 'not initialized' process name(pid)
'filerep main process(14611)' filerep state 'not initialized'    0        cdbfilerep.c    3371
2012-06-12 13:16:18.617047
EDT            p14612    th802662304                0            seg-1                    LOG    0    CHANGETRACKING:
ChangeTracking_RetrieveIsTransitionToInsync() found
insync_transition_completed:'false' full
resync:'false'                            0        cdbresynchronizechangetracking.c    2522
2012-06-12 13:16:18.617113
EDT            p14612    th802662304                0            seg-1                    LOG    0    CHANGETRACKING:
ChangeTracking_RetrieveIsTransitionToResync() found
resync_transition_completed:'false' full
resync:'false'                            0        cdbresynchronizechangetracking.c    2559
2012-06-12 13:16:18.746870
EDT            p14612    th802662304                0            seg-1                    LOG    0    searching for
last
checkpoint location for creating the initial resynchronize
changetracking                            0        xlog.c    10836
2012-06-12 13:16:18.747318
EDT            p14612    th802662304                0            seg-1                    LOG    0    record with zero
length at 14/48000070                            0        xlog.c    4182
2012-06-12 13:16:18.747491
EDT            p14612    th802662304                0            seg-1                    LOG    0    scanned through
1
initial xlog records since last checkpoint for writing into the
resynchronize change log                            0        cdbresynchronizechangetracking.c    206
2012-06-12 13:16:18.750830
EDT            p14624    th802662304                0            seg-1                    LOG    0    database system
was
shut down at 2012-06-12 11:00:13 EDT                            0        xlog.c    6326
2012-06-12 13:16:18.750987
EDT            p14624    th802662304                0            seg-1                    LOG    0    checkpoint record
is
at 14/48000020                            0        xlog.c    6425
2012-06-12 13:16:18.751016
EDT            p14624    th802662304                0            seg-1                    LOG    0    redo record is
at
14/48000020; undo record is at 14/42AC2118; shutdown
TRUE                            0        xlog.c    6534
2012-06-12 13:16:18.751041
EDT            p14624    th802662304                0            seg-1                    LOG    0    next transaction
ID:
0/4553423; next OID: 241771                            0        xlog.c    6538
2012-06-12 13:16:18.751065
EDT            p14624    th802662304                0            seg-1                    LOG    0    next MultiXactId:
271;
next MultiXactOffset: 549                            0        xlog.c    6541
2012-06-12 13:16:18.796637
EDT            p14624    th802662304                0            seg-1                    PANIC    XX000    invalid
redo/undo record in shutdown checkpoint
(xlog.c:6576)                            0        xlog.c    6576    "Stack trace:
1    0xa59f75 postgres errstart + 0x595
2    0x50f7ac postgres StartupXLOG + 0x1b8c
3    0x51778d postgres StartupProcessMain + 0x2fd
4    0x590746 postgres AuxiliaryProcessMain + 0x796
5    0x85fe54 postgres <symbol not found> + 0x85fe54
6    0x86003a postgres StartMasterOrPrimaryPostmasterProcesses + 0x3a
7    0x86ffaf postgres doRequestedPrimaryMirrorModeTransitions + 0xd9f
8    0x86bc4a postgres PostmasterMain + 0x1f8a
9    0x772bda postgres main + 0x4da
10   0x2af72ebc7994 libc.so.6 __libc_start_main + 0xf4
11   0x47bf49 postgres <symbol not found> + 0x47bf49