Hi there.

I've encountered an issue with my Galera Cluster.

I have 4 Nodes clustered across 2 different physical locations with a substantial link between them.

I've recently had 2 node crashes (different nodes with the same error message)

I'm getting the following in the server log:

141124 7:26:54 [Warning] WSREP: SQL statement was ineffective, THD: 832, buf: 175
QUERY: commit
=> Skipping replication
141124 7:26:54 [ERROR] WSREP: FSM: no such a transition ROLLED_BACK -> ROLLED_BACK
141124 7:26:54 [ERROR] mysqld got signal 6 ;
This could be because you hit a bug. It is also possible that this binary
or one of the libraries it was linked against is corrupt, improperly built,
or misconfigured. This error can also be caused by malfunctioning hardware.

To report this bug, see http://kb.askmonty.org/en/reporting-bugs

We will try our best to scrape up some info that will hopefully help
diagnose the problem, but since we have already crashed,
something is definitely wrong and this may fail.

Server version: 5.5.37-MariaDB-wsrep-log
key_buffer_size=134217728
read_buffer_size=131072
max_used_connections=178
max_threads=501
thread_count=76
It is possible that mysqld could use up to
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 1225846 K bytes of memory
Hope that's ok; if not, decrease some variables in the equation.

Thread pointer: 0x0x7f1d92e94000
Attempting backtrace. You can use the following information to find out
where mysqld died. If you see no messages after this, something went
terribly wrong...
stack_bottom = 0x7f30a38d9c38 thread_stack 0x48000
/usr/sbin/mysqld(my_print_stacktrace+0x2b)[0xa9226b]
/usr/sbin/mysqld(handle_fatal_signal+0x398)[0x6ea9d8]
/lib64/libpthread.so.0[0x349440f710]
/lib64/libc.so.6(gsignal+0x35)[0x3494032925]
/lib64/libc.so.6(abort+0x175)[0x3494034105]
/usr/lib64/galera/libgalera_smm.so(ZN6galera3FSMINS_9TrxHandle5StateENS1_10TransitionENS_10EmptyGuardENS_11EmptyActionEE8shift_toES2+0x2d9)[0x7f31e956b4d9]
/usr/lib64/galera/libgalera_smm.so(_ZN6galera13ReplicatorSMM13post_rollbackEPNS_9TrxHandleE+0x2e)[0x7f31e958628e]
/usr/lib64/galera/libgalera_smm.so(galera_post_rollback+0x68)[0x7f31e959fd88]
/usr/sbin/mysqld[0x691375]
/usr/sbin/mysqld[0x691488]
/usr/sbin/mysqld(_Z17ha_rollback_transP3THDb+0xe6)[0x6ed4c6]
/usr/sbin/mysqld(_Z15ha_commit_transP3THDb+0x1e2)[0x6ed7d2]
/usr/sbin/mysqld(_Z12trans_commitP3THD+0x45)[0x66ce65]
/usr/sbin/mysqld(_Z21mysql_execute_commandP3THD+0x2c80)[0x5a7df0]
/usr/sbin/mysqld[0x5abf94]
/usr/sbin/mysqld[0x5ac37b]
/usr/sbin/mysqld(_Z16dispatch_command19enum_server_commandP3THDPcj+0x1889)[0x5adfd9]
/usr/sbin/mysqld(_Z10do_commandP3THD+0x11c)[0x5ae73c]
/usr/sbin/mysqld(_Z26threadpool_process_requestP3THD+0xa7)[0x690457]
/usr/sbin/mysqld[0x6c2115]
/lib64/libpthread.so.0[0x34944079d1]
/lib64/libc.so.6(clone+0x6d)[0x34940e8b5d]

Trying to get some variables.
Some pointers may be invalid and cause the dump to abort.
Query (0x7f1d9558b018): is an invalid pointer
Connection ID (thread ID): 832
Status: NOT_KILLED

Optimizer switch: index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=off,table_elimination=on,extended_keys=off

The manual page at http://dev.mysql.com/doc/mysql/en/crashing.html contains
information that should help you find out what is causing the crash.
141124 07:26:55 mysqld_safe Number of processes running now: 0
141124 07:26:55 mysqld_safe WSREP: not restarting wsrep node automatically
141124 07:26:55 mysqld_safe mysqld from pid file /var/lib/mysql/mysql.pid ended

The following Warning appears multiple times in the logs for both servers

[Warning] WSREP: SQL statement was ineffective, THD: 832, buf: 175
QUERY: commit
=> Skipping replication

I've definitely got all 4 nodes configured with bin_log=ROW and no auto_increment settings so I don't know whats causing this to occur during normal operations.