build farm machine using <make -j 8> mixed results

I change the build-farm.conf file to have the following make line:

make => 'make -j 8', # or gmake if required. can include path if necessary.

2 pass, 4 fail. Is this a build configuration you want to pursue? I can either create a new machine, or change one of my existing machines. Makes no difference to me.

roberts-imac:build-farm-4.7-j robert$ time ./run_branches.pl --run-all --test
Sat Sep 1 09:26:49 2012: buildfarm run for CHANGEME:HEAD starting
[09:26:49] checking out source ...
[09:27:59] checking if build run needed ...
[09:27:59] copying source to pgsql.54279 ...
[09:28:03] running configure ...
[09:28:25] running make ...
[09:28:45] running make check ...
Branch: HEAD
Stage Check failed with status 2
Sat Sep 1 09:29:09 2012: buildfarm run for CHANGEME:REL9_2_STABLE starting
[09:29:09] checking out source ...
[09:29:57] checking if build run needed ...
[09:29:57] copying source to pgsql.70926 ...
[09:29:58] running configure ...
[09:30:18] running make ...
[09:30:45] running make check ...
[09:31:09] running make contrib ...
[09:31:12] running make install ...
[09:31:15] running make contrib install ...
[09:31:16] setting up db cluster (C)...
[09:31:19] starting db (C)...
[09:31:20] running make installcheck (C)...
[09:31:39] restarting db (C)...
[09:31:51] running make isolation check ...
[09:32:00] restarting db (C)...
[09:32:12] running make PL installcheck (C)...
Branch: REL9_2_STABLE
Stage PLCheck-C failed with status 2
Sat Sep 1 09:32:29 2012: buildfarm run for CHANGEME:REL9_1_STABLE starting
[09:32:29] checking out source ...
[09:33:08] checking if build run needed ...
[09:33:08] copying source to pgsql.94883 ...
[09:33:10] running configure ...
[09:33:30] running make ...
[09:33:54] running make check ...
[09:34:18] running make contrib ...
[09:34:21] running make install ...
[09:34:23] running make contrib install ...
[09:34:24] setting up db cluster (C)...
[09:34:26] starting db (C)...
[09:34:27] running make installcheck (C)...
[09:34:47] restarting db (C)...
[09:34:59] running make isolation check ...
[09:35:16] restarting db (C)...
[09:35:28] running make PL installcheck (C)...
Branch: REL9_1_STABLE
Stage PLCheck-C failed with status 2
Sat Sep 1 09:35:46 2012: buildfarm run for CHANGEME:REL9_0_STABLE starting
[09:35:46] checking out source ...
[09:36:08] checking if build run needed ...
[09:36:08] copying source to pgsql.18851 ...
[09:36:10] running configure ...
[09:36:28] running make ...
[09:37:00] running make check ...
[09:37:23] running make contrib ...
[09:37:27] running make install ...
[09:37:30] running make contrib install ...
[09:37:32] setting up db cluster (C)...
[09:37:34] starting db (C)...
[09:37:35] running make installcheck (C)...
[09:37:52] restarting db (C)...
[09:38:04] running make PL installcheck (C)...
[09:38:06] restarting db (C)...
[09:38:18] running make contrib installcheck (C)...
[09:38:30] stopping db (C)...
[09:38:31] running make ecpg check ...
[09:38:43] OK
Branch: REL9_0_STABLE
All stages succeeded
Sat Sep 1 09:38:43 2012: buildfarm run for CHANGEME:REL8_4_STABLE starting
[09:38:43] checking out source ...
[09:38:57] checking if build run needed ...
[09:38:57] copying source to pgsql.45071 ...
[09:38:59] running configure ...
[09:39:19] running make ...
[09:39:46] running make check ...
[09:40:14] running make contrib ...
[09:40:17] running make install ...
[09:40:23] running make contrib install ...
[09:40:25] setting up db cluster (C)...
[09:40:30] starting db (C)...
[09:40:31] running make installcheck (C)...
[09:40:47] restarting db (C)...
[09:40:59] running make PL installcheck (C)...
[09:41:01] restarting db (C)...
[09:41:13] running make contrib installcheck (C)...
[09:41:25] stopping db (C)...
[09:41:26] running make ecpg check ...
[09:41:44] OK
Branch: REL8_4_STABLE
All stages succeeded
Sat Sep 1 09:41:44 2012: buildfarm run for CHANGEME:REL8_3_STABLE starting
[09:41:44] checking out source ...
[09:42:39] checking if build run needed ...
[09:42:39] copying source to pgsql.80222 ...
[09:42:42] running configure ...
[09:43:03] running make ...
[09:43:38] running make check ...
[09:44:04] running make contrib ...
[09:44:09] running make install ...
[09:44:14] running make contrib install ...
[09:44:17] setting up db cluster (C)...
[09:44:20] starting db (C)...
[09:44:21] running make installcheck (C)...
[09:44:39] restarting db (C)...
[09:44:51] running make PL installcheck (C)...
[09:44:52] restarting db (C)...
[09:45:05] running make contrib installcheck (C)...
Branch: REL8_3_STABLE
Stage ContribCheck-C failed with status 2