Disclaimer: this is a rough concept only that require testing in a non-production environment obviously.
Disclaimer 2: This is general advice from a community user and I also don't have much time but feel your pain enough to offer this on an as is basis.

I'd be looking at something like this to use gdb to attach to the running process and print out information http://www.outofcore.com/2011/06/scripted-debug-using-gdb/.

So trapped points would be (from source mysys/my_malloc.c):
https://github.com/MariaDB/server/blob/a14638581b4c8ef175e68dccff07967d819b3b7e/mysys/my_malloc.c#L130

1. my_free
2. my_realloc
3. my_malloc

Ideally logging a returned (using ``print pointer, my_flags, size``) pointer, flags and size from malloc/realloc calls, the oldptr from the realloc call, and the ptr argument from the free call. At each of these breakpoints logging the backtrace of the current thread. Hopefully the output from this with a bit of analysis can identify the backtrack where memory is allocated by not freed.

gdb can attach to a process (using -p) and there is a batch mode for the script.

I feel your pain about hard to debug memory leaks (mine was my second bug report MDEV-4974). Wish I'd though of this at that time (but I didn't know enough then).

PS. If you do write the gdb script please include if for someone else

Did you look at `MEMORY_USED` values in `INFORMATION_SCHEMA.PROCESSLIST` and `SHOW STATUS`? Anything notable?

Thanks for the replies and info!

`select MEMORY_USED from INFORMATION_SCHEMA.PROCESSLIST;` looks fine. I took that a step further and shut off the application in my test environment and confirmed no connections to the db other than my session (MEMORY_USED confirmed to no longer show those processes). The memory usage stops getting worse with the db idle (expected), but doesn’t release any memory either. The mysqld process still shows it is still using much more memory than it should be when taking into account relevant cache and buffer pool values (innodb_buffer_pool_size + innodb_additional_mem_pool_size + innodb_log_buffer_size + query_cache_size). I have left my test off for several hours now, to confirm mysqld memory use stays the same.

Could this be the same as MDEV-11883?
Edit: never mind - its probably not. that has to do with read only filesystems.

Is it a master or a slave? File names in attachment suggest that it could be a master, but it has rpl-do-db and a big gtid_slave_pos, so it's unclear.

It is only the master that has the problem.

We have been able to narrow down where the problem resides.

We are using per query timeouts. Here is an example from the attached binlog.

SET STATEMENT max_statement_time=4.655, long_query_time=3.9200000000000004, sql_mode='STRICT_ALL_TABLES' FOR ....

We made a modification our app to remove the prefix as a test, and we could no longer reproduce the memory leak. Changing the timeouts from per query to per session does dramatically slow the memory leak, but doesn't look to resolve it completely.