BUG #3179: crash when canceling avacuum

The following bug has been logged online:

Bug reference: 3179
Logged by:
Email address: cstdenis(at)ctgameinfo(dot)com
PostgreSQL version: 8.2.0
Operating system: FreeBSD 6.2
Description: crash when canceling avacuum
Details:

I started a vacuumdb -a -v -z then changed my mind to cancled it under
pgadminIII. First try didn't seem to work to I clicked the button a few more
times. Whole server crashed.

Don't think I can reproduce it (and don't want to try) since I think it was
a race-condition or something.

It generated a core file while I have generated a backtrace of here.

ayu# gdb /usr/local/bin/postgres ./postgres.core
GNU gdb 6.1.1 [FreeBSD]
Copyright 2004 Free Software Foundation, Inc.
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are
welcome to change it and/or distribute copies of it under certain
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Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for details.
This GDB was configured as "i386-marcel-freebsd"...(no debugging symbols
found)...
Core was generated by `postgres'.
Program terminated with signal 6, Aborted.
Reading symbols from /usr/local/lib/libintl.so.6...(no debugging symbols
found)...done.
Loaded symbols for /usr/local/lib/libintl.so.6
Reading symbols from /usr/lib/libssl.so.4...(no debugging symbols
found)...done.
Loaded symbols for /usr/lib/libssl.so.4
Reading symbols from /lib/libcrypto.so.4...(no debugging symbols
found)...done.
Loaded symbols for /lib/libcrypto.so.4
Reading symbols from /lib/libcrypt.so.3...(no debugging symbols
found)...done.
Loaded symbols for /lib/libcrypt.so.3
Reading symbols from /lib/libm.so.4...(no debugging symbols found)...done.
Loaded symbols for /lib/libm.so.4
Reading symbols from /lib/libc.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib/libc.so.6
Reading symbols from /usr/local/lib/libiconv.so.3...(no debugging symbols
found)...done.
Loaded symbols for /usr/local/lib/libiconv.so.3
Reading symbols from /libexec/ld-elf.so.1...(no debugging symbols
found)...done.
Loaded symbols for /libexec/ld-elf.so.1
#0 0x286243df in kill () from /lib/libc.so.6
(gdb) bt
#0 0x286243df in kill () from /lib/libc.so.6
#1 0x2862437e in raise () from /lib/libc.so.6
#2 0x2862309e in abort () from /lib/libc.so.6
#3 0x082ef19b in errfinish ()
#4 0x082ef6e0 in elog_finish ()
#5 0x080aec21 in xactGetCommittedChildren ()
#6 0x080b1175 in AbortCurrentTransaction ()
#7 0x0822ec0b in PostgresMain ()
#8 0x081f1816 in ClosePostmasterPorts ()
#9 0x081f38b7 in PostmasterMain ()
#10 0x081a358f in main ()
(gdb)