[#MDEV-32176] Contention in ha_innobase::info_low (dict_table::lock_mutex

Running sysbench with Intel's VTune, I've noticed there is large-ish contention in ha_innobase::info_low(), if flag contains HA_STATUS_VARIABLE.

It is a cached workload, database is started with large enough buffer pool 10G.
sysbench is run for 1 table x 1000000 rows, oltp_point_select, 400 users.

.\sysbench.exe oltp_point_select --table-size=10000000 --mysql-user=root --report-interval=1 --time=30 --threads=400 --point-selects=0 --mysql-db=sbtest --mysql-ssl=off --histogram=1 run

I'm attaching the flamegraph screenshots (sorry for this, but it does not seem to be possible to export that in svg from VTune)

		ib_table->stats_mutex_lock();

		ut_a(ib_table->stat_initialized);

		n_rows = ib_table->stat_n_rows;

		stat_clustered_index_size

			= ib_table->stat_clustered_index_size;

		stat_sum_of_other_index_sizes

			= ib_table->stat_sum_of_other_index_sizes;

		ib_table->stats_mutex_unlock();

ntdll.dll ! ZwWaitForAlertByThreadId

ntdll.dll ! RtlpWaitOnAddressWithTimeout + 0x80

ntdll.dll ! RtlpWaitOnAddress + 0xd7

ntdll.dll ! RtlWaitOnAddress + 0x12

KERNELBASE.dll ! WaitOnAddress + 0x32

server.dll ! srw_mutex_impl<1>::wait + 0x18 - srw_lock.cc:202

server.dll ! srw_mutex_impl<1>::wait_and_lock + 0x60 - srw_lock.cc:324

server.dll ! srw_mutex_impl<1>::wr_lock + 0x10 - srw_lock.h:134

server.dll ! dict_table_t::lock_mutex_lock + 0x7 - dict0mem.h:2011

server.dll ! dict_table_t::stats_mutex_lock - dict0mem.h:2039

server.dll ! ha_innobase::info_low + 0x202 - ha_innodb.cc:14787

server.dll ! make_join_statistics + 0x20c - sql_select.cc:5499

server.dll ! JOIN::optimize_inner + 0x1cff - sql_select.cc:2625

server.dll ! JOIN::optimize + 0x8b - sql_select.cc:1944

server.dll ! mysql_select + 0x2e1 - sql_select.cc:5235

server.dll ! handle_select + 0x1f9 - sql_select.cc:628

server.dll ! execute_sqlcom_select + 0x2e5 - sql_parse.cc:6012

server.dll ! mysql_execute_command + 0xac6 - sql_parse.cc:3911

server.dll ! Prepared_statement::execute + 0x2b3 - sql_prepare.cc:5027

...

It seems like mutual exclusion is an overkill here, as no data is being changed. Perhaps a slim rwlock would be better?

[MDEV-32176] Contention in ha_innobase::info_low (dict_table::lock_mutex_lock) Created: 2023-09-15 Updated: 2023-09-15
Status:	Open
Project:	MariaDB Server
Component/s:	Storage Engine - InnoDB
Affects Version/s:	11.3
Fix Version/s:	None

[MDEV-32176] Contention in ha_innobase::info_low (dict_table::lock_mutex_lock) Created: 2023-09-15 Updated: 2023-09-15