I build libmariadbclient18 with symbols (below) and got a new backtrace of the hanging process.
I guess the only choice is to try with the newer lib that comes with Debian Buster or give up use of db_cluster module with MySQL.
-- Juha
---start 24717 ----------------------------------------------------- [Thread debugging using libthread_db enabled] Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1". 0x00007f517466d8a0 in __poll_nocancel () at ../sysdeps/unix/syscall-template.S:84 84 ../sysdeps/unix/syscall-template.S: No such file or directory. #0 0x00007f517466d8a0 in __poll_nocancel () at ../sysdeps/unix/syscall-template.S:84 No locals. #1 0x00007f51725f3ef1 in poll (__timeout=2000, __nfds=1, __fds=0x7ffed132f808) at /usr/include/x86_64-linux-gnu/bits/poll2.h:46 No locals. #2 vio_io_wait (vio=vio@entry=0x560529eb39d8, event=event@entry=VIO_IO_EVENT_READ, timeout=2000) at ./vio/viosocket.c:992 ret = <optimized out> revents = <optimized out> pfd = {fd = 18, events = 3, revents = 0} state = {m_flags = 3509778656, m_socket = 0x7ffed132f820, m_thread = 0x0, m_number_of_bytes = 21474836512, m_timer_start = 140732408199414, m_timer = 0x7ffed132f8fc, m_operation = 3509778680, m_src_file = 0x7ffed132f8fc "\376\177", m_src_line = 16, m_wait = 0x7f517398d010} #3 0x00007f51725f3f78 in vio_socket_io_wait (vio=vio@entry=0x560529eb39d8, event=event@entry=VIO_IO_EVENT_READ) at ./vio/viosocket.c:108 timeout = <optimized out> ret = -516 #4 0x00007f51725f4082 in vio_read (vio=vio@entry=0x560529eb39d8, buf=0x560529eb3bd8 "\001", size=size@entry=16384) at ./vio/viosocket.c:184 error = <optimized out> ret = <optimized out> flags = 64 #5 0x00007f51725f4145 in vio_read_buff (vio=0x560529eb39d8, buf=0x560529eb7be8 "\001", size=4) at ./vio/viosocket.c:232 rc = <optimized out> #6 0x00007f51725cfe91 in my_real_read (net=0x7f5173d674e0, complen=complen@entry=0x7ffed132f9f8, header=0 '\000') at ./sql/net_serv.cc:877 pos = 0x560529eb7be8 "\001" length = <optimized out> i = <optimized out> retry_count = <optimized out> len = <optimized out> expect_error_packet = <optimized out> alarmed = 0 '\000' remain = 4 #7 0x00007f51725d0d1c in my_net_read_packet (net=net@entry=0x7f5173d674e0, read_from_server=read_from_server@entry=0 '\000') at ./sql/net_serv.cc:1140 len = <optimized out> complen = 0 #8 0x00007f51725c28af in cli_safe_read (mysql=mysql@entry=0x7f5173d674e0) at ./sql-common/client.c:587 net = 0x7f5173d674e0 len = <optimized out> #9 0x00007f51725c8323 in cli_advanced_command (mysql=0x7f5173d674e0, command=<optimized out>, header=0x0, header_length=0, arg=0x0, arg_length=0, skip_check=0 '\000', stmt=0x0) at ./sql-common/client.c:729 net = 0x7f5173d674e0 result = 0 '\000' stmt_skip = <optimized out> #10 0x00007f51725be2a1 in mysql_ping (mysql=<optimized out>) at ./libmysql/libmysql.c:982 res = <optimized out> #11 0x00007f5172bb14e6 in db_mysql_submit_query (_h=0x7f51739ecff0, _s=0x7f5172fff2d0 <sql_str>) at km_dbase.c:83 t = 1568791290 i = 0 code = 22021 __func__ = "db_mysql_submit_query" #12 0x00007f5172deeb88 in db_do_submit_query (_h=0x7f51739ecff0, _query=0x7f5172fff2d0 <sql_str>, submit_query=0x7f5172bb1149 <db_mysql_submit_query>) at db_query.c:58 ret = 32593 tvb = {tv_sec = 94580176772804, tv_usec = 139987808866288} tve = {tv_sec = 109108585221, tv_usec = 1365799600152} tz = {tz_minuteswest = 24, tz_dsttime = 65147} tdiff = 1755212864 __func__ = "db_do_submit_query" #13 0x00007f5172df11ca in db_do_insert_cmd (_h=0x7f51739ecff0, _k=0x7f51689e6960 <db_keys>, _v=0x7f51689e6c40 <db_vals>, _n=24, val2str=0x7f5172baf7b8 <db_mysql_val2str>, submit_query=0x7f5172bb1149 <db_mysql_submit_query>, mode=0) at db_query.c:242 off = 707 ret = 318 __func__ = "db_do_insert_cmd" ...