EMQX-9101 mnesia unregister hook

[SergeTupchiy]

No description provided.

[ieQu1]

Q: Is this stop function called before or after application controller shuts down the supervisor?
I think we need to unregister hook while the rlog_server processes are still running to avoid error message.

[SergeTupchiy]

It's called after supervision tree is shutdown.
Initially I've added it to prep_stop/1 callback, but than thought that it might be too early to un-register it before all the app processes are shutdown..
A naive test shows that un-registering the hook in application stop/1 callback is enough to fix the crashes upon restarting mria:

$ . ~/kerl/25.1.2-3-emqx/activate
$ make clean
$ PROFILE=emqx-enterprise make emqx-enterprise
$ _build/emqx-enterprise/rel/emqx/bin/emqx console_clean 
(search)`ensure': application:ensure_all_started(mria).                    
{ok,[inets,crypto,asn1,public_key,ssl,gen_rpc,replayq,
     snabbkaffe,optvar,mria]}
(emqx@127.0.0.1)2> 
(emqx@127.0.0.1)2> 
(search)`mria:st': mria:stop(),application:ensure_all_started(mria).
2023-03-22T12:48:39.983144+02:00 [warning] msg: Stopping mria, mfa: mria:stop/1, line: 130, reason: stop
{ok,[mria]}
(emqx@127.0.0.1)3> mria:stop(),application:ensure_all_started(mria).
2023-03-22T12:48:42.148922+02:00 [warning] msg: Stopping mria, mfa: mria:stop/1, line: 130, reason: stop
{ok,[mria]}
(emqx@127.0.0.1)4> mria:stop(),application:ensure_all_started(mria).
2023-03-22T12:48:42.892593+02:00 [warning] msg: Stopping mria, mfa: mria:stop/1, line: 130, reason: stop
{ok,[mria]}
(emqx@127.0.0.1)5> mria:stop(),application:ensure_all_started(mria).
2023-03-22T12:48:43.474105+02:00 [warning] msg: Stopping mria, mfa: mria:stop/1, line: 130, reason: stop
{ok,[mria]}

The same test with the previous OTP (without un-registering):

$ kerl_deactivate 
$ . ~/kerl/25.1.2-2-emqx/activate
$ make clean
$ PROFILE=emqx-enterprise make emqx-enterprise
$ _build/emqx-enterprise/rel/emqx/bin/emqx console_clean 
(search)`mria': application:ensure_all_started(mria).           
{ok,[inets,crypto,asn1,public_key,ssl,gen_rpc,replayq,
     snabbkaffe,optvar,mria]}
(emqx@127.0.0.1)2> 
(emqx@127.0.0.1)2> 
(emqx@127.0.0.1)2> 
(emqx@127.0.0.1)2> 
(search)`mria:st': mria:stop(),application:ensure_all_started(mria).
2023-03-22T12:52:29.959562+02:00 [warning] msg: Stopping mria, mfa: mria:stop/1, line: 130, reason: stop
2023-03-22T12:52:30.015153+02:00 [error] Mnesia('emqx@127.0.0.1'): ** ERROR ** Mnesia post_commit hook failed: error:badarg, Stacktrace:[{erlang,send,['$mria_meta_shard',{trans,{tid,13,<0.2267.0>},#{disc_copies => [],disc_only_copies => [],ext => [],node => 'emqx@127.0.0.1',ram_copies => [{{mria_schema,mria_schema},{mria_schema,mria_schema,'$mria_meta_shard',ram_copies,[{type,ordered_set},{record_name,mria_schema},{attributes,[mnesia_table,shard,storage,config]}]},write}],schema_ops => []}}],[{error_info,#{module => erl_erts_errors}}]},{mria_rlog_server,dispatch,3,[{file,"mria_rlog_server.erl"},{line,105}]},{mnesia_hook,do_post_commit,2,[{file,"mnesia_hook.erl"},{line,69}]},{mnesia_tm,do_commit,3,[{file,"mnesia_tm.erl"},{line,1788}]},{mnesia_tm,multi_commit,5,[{file,"mnesia_tm.erl"},{line,1422}]},{mnesia_tm,apply_fun,3,[{file,"mnesia_tm.erl"},{line,843}]},{mnesia_tm,execute_transaction,5,[{file,"mnesia_tm.erl"},{line,818}]},{mria_schema,boostrap,0,[{file,"mria_schema.erl"},{line,335}]}]
{ok,[mria]}
(emqx@127.0.0.1)3> 
(emqx@127.0.0.1)3> mria:stop(),application:ensure_all_started(mria).
2023-03-22T12:52:31.244164+02:00 [warning] msg: Stopping mria, mfa: mria:stop/1, line: 130, reason: stop
2023-03-22T12:52:31.303299+02:00 [error] Mnesia('emqx@127.0.0.1'): ** ERROR ** Mnesia post_commit hook failed: error:badarg, Stacktrace:[{erlang,send,['$mria_meta_shard',{trans,{tid,14,<0.2328.0>},#{disc_copies => [],disc_only_copies => [],ext => [],node => 'emqx@127.0.0.1',ram_copies => [{{mria_schema,mria_schema},{mria_schema,mria_schema,'$mria_meta_shard',ram_copies,[{type,ordered_set},{record_name,mria_schema},{attributes,[mnesia_table,shard,storage,config]}]},write}],schema_ops => []}}],[{error_info,#{module => erl_erts_errors}}]},{mria_rlog_server,dispatch,3,[{file,"mria_rlog_server.erl"},{line,105}]},{mnesia_hook,do_post_commit,2,[{file,"mnesia_hook.erl"},{line,69}]},{mnesia_tm,do_commit,3,[{file,"mnesia_tm.erl"},{line,1788}]},{mnesia_tm,multi_commit,5,[{file,"mnesia_tm.erl"},{line,1422}]},{mnesia_tm,apply_fun,3,[{file,"mnesia_tm.erl"},{line,843}]},{mnesia_tm,execute_transaction,5,[{file,"mnesia_tm.erl"},{line,818}]},{mria_schema,boostrap,0,[{file,"mria_schema.erl"},{line,335}]}]
{ok,[mria]}