Hello.

I have deployed a Moodle Cluster version 3.9 with 3 webservers and 4 MariaDB 10.5.5 nodes with Galera Cluster (I also tried Mariadb 10.4.13) and Maxscale as Loadbalancer.

But my Galera cluster constantly crashing, I have checked the logs and found the following:

201007 16:48:02 [ERROR] mysqld got signal 11;
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 https://mariadb.com/kb/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: 10.5.5-MariaDB-1: 10.5.5 + maria ~ buster-log
key_buffer_size = 134217728
read_buffer_size = 2097152
max_used_connections = 12
max_threads = 1502
thread_count = 16
It is possible that mysqld could use up to
key_buffer_size + (read_buffer_size + sort_buffer_size) * max_threads = 9396920 K bytes of memory
Hope that's ok; if not, decrease some variables in the equation.
Thread pointer: 0x7fa174000c18
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 = 0x7fa7440bad58 thread_stack 0x49000
/ usr / sbin / mariadbd (my_print_stacktrace + 0x2e) [0x55c94d9b9ece]
Printing to addr2line failed
/ usr / sbin / mariadbd (handle_fatal_signal + 0x485) [0x55c94d43c2d5]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x12730)[0x7fa78d0ac730]
/ usr / sbin / mariadbd (_ZN8MDL_lock18reschedule_waitersEv + 0x1b) [0x55c94d34733b]
/ usr / sbin / mariadbd (_ZN8MDL_lock13remove_ticketEP7LF_PINSMS_NS_11Ticket_listEP10MDL_ticket + 0x94) [0x55c94d347
/ usr / sbin / mariadbd (_ZN11MDL_context12release_lockE17enum_mdl_durationP10MDL_ticket + 0x24) [0x55c94d347f24]
/ usr / sbin / mariadbd (_ZN22Item_func_release_lock7val_intEv + 0x20a) [0x55c94d49fd3a]
/ usr / sbin / mariadbd (_ZNK12Type_handler14Item_send_longEP4ItemP8ProtocolP8st_value + 0x19) [0x55c94d3aa9f9]
/ usr / sbin / mariadbd (_ZN8Protocol19send_result_set_rowEP4ListI4ItemE + 0xa3) [0x55c94d197723]
/ usr / sbin / mariadbd (_ZN11select_send9send_dataER4ListI4ItemE + 0x32) [0x55c94d202062]
/ usr / sbin / mariadbd (_ZN4JOIN10exec_innerEv + 0xbe6) [0x55c94d2ab2b6]
/ usr / sbin / mariadbd (_ZN4JOIN4execEv + 0x37) [0x55c94d2ab557]
/ usr / sbin / mariadbd (_Z12mysql_selectP3THDP10TABLE_LISTR4ListI4ItemEPS4_jP8st_orderS9_S7_S9_yP13select_result
/ usr / sbin / mariadbd (_Z13handle_selectP3THDP3LEXP13select_resultm + 0x14e) [0x55c94d2aa25e]
/ usr / sbin / mariadbd (+ 0x751539) [0x55c94d249539]
/ usr / sbin / mariadbd (_Z21mysql_execute_commandP3THD + 0x13ff) [0x55c94d252241]
/ usr / sbin / mariadbd (_Z11mysql_parseP3THDPcjP12Parser_statebb + 0x1bc) [0x55c94d244583]
/ usr / sbin / mariadbd (+ 0x74c070) [0x55c94d244070]
/ usr / sbin / mariadbd (_Z16dispatch_command19enum_server_commandP3THDPcjbb + 0x242c) [0x55c94d24ffe5]
/ usr / sbin / mariadbd (_Z10do_commandP3THD + 0x110) [0x55c94d250488]
/ usr / sbin / mariadbd (_Z24do_handle_one_connectionP7CONNECTb + 0x4c1) [0x55c94d33e031]
/ usr / sbin / mariadbd (handle_one_connection + 0x5d) [0x55c94d33e3bd]
/ usr / sbin / mariadbd (+ 0xb6b27b) [0x55c94d66327b]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x7fa3)[0x7fa78d0a1fa3]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x3f)[0x7fa78c5a54cf]
Trying to get some variables.
Some pointers may be invalid and cause the dump to abort.
Query (0x7fa1740103b0): SELECT RELEASE_LOCK ('6be869571d63b89d2c50fcb2c53b64486bce9a27') AS unlocked
Connection ID (thread ID): 6816
Status: NOT_KILLED

From this the following query stands out:

SELECT RELEASE_LOCK ('6be869571d63b89d2c50fcb2c53b64486bce9a27') AS unlocked

Which I believe the following code that calls this query has recently been implemented in Moodle 3.9:

https://github.com/moodle/moodle/blob/d4d798e6843885f0176732fb44949f316203192e/lib/classes/lock/mysql_lock_factory.php#L141

Also mention that I have deployed in production this same architecture with version 3.6 and 3.8 of Moodle which continue to work without problems.

I thank all in advance for the support.