MariaDB 10.5 and Memory Instrumentation in Performance Schema - First Steps

Chances are high for me to speak about MariaDB 10.5 at the upcoming MariaDB Server Fest Online Conference (as my related talk was accepted), so it's time to start writing about it. In this post I am going to do basic checks of the new and long wanted Performance Schema memory instrumentation feature finally ported from MySQL 5.7. Until recently we mostly had to use OS level tools for memory instrumentation, like perf or heap profilers etc.

As usual (see here and there) when I am serious about working with some open source software and formally supporting it, I start with checking how to build it from GitHub source on my own hardware and/or VMs. This time I've tried the usual steps to build MariaDB 10.5.5 on my gold old Ubuntu 16.04 netbook (from fc -l output):

1984     cd git/server/
1985     git branch
1986     git checkout 10.5
1987     git pull
1988     git submodule update --init --recursive
1989     rm CMakeCache.txt
1990     cd build/
1991     rm -rf *
1992     cmake .. -DCMAKE_BUILD_TYPE=RelWithDebInfo -DWITH_SSL=system -DWITH_ZLIB=bundled -DMYSQL_MAINTAINER_MODE=OFF -DENABLED_LOCAL_INFILE=1 -DWITH_JEMALLOC=system -DWITH_INNODB_DISALLOW_WRITES=ON -DCMAKE_INSTALL_PREFIX=/home/openxs/dbs/maria10.5
1993     time make -j 3
...
2001     rm -rf /home/openxs/dbs/maria10.5
2002     make install && make clean
2003     cd /home/openxs/dbs/maria10.5
...
2005     scripts/mysql_install_db --no-defaults
2006     bin/mysqld_safe --no-defaults --port=3309 --socket=/tmp/mariadb.sock --performance_schema=ON &

I am using out of source build in a separate build subdirectory and clean up the remaining of older builds just in case. Options used are typical for this box. I do not disable the TokuDB engine explicitly as it's no longer included anyway.  

Then I removed previous instance, initialized the database and started it as usual, via mysqld_safe with explicit option to enable Performance Schema as it's disabled in MariaDB by default. Note these details though:

openxs@ao756:~/dbs/maria10.5$ ls -l bin/mysqld
lrwxrwxrwx 1 openxs openxs 8 сер  9 14:04 bin/mysqld -> mariadbd
openxs@ao756:~/dbs/maria10.5$ ls -l bin/mariadbd
-rwxr-xr-x 1 openxs openxs 213124184 сер  9 13:57 bin/mariadbd
openxs@ao756:~/dbs/maria10.5$ ls -l ../maria10.4/bin/mysqld
-rwxr-xr-x 1 openxs openxs 178385776 сер  5 19:18 ../maria10.4/bin/mysqld
openxs@ao756:~/dbs/maria10.5$ ls -l ../8.0/bin/mysqld
-rwxr-xr-x 1 openxs openxs 749000640 лип 13 21:35 ../8.0/bin/mysqld

All the mysql* binaries are now symbolic links to mariadb* ones. Also note the relative sizes of the non-stripped binaries comparing to MariaDB 10.4 and MySQL 8.0.21 (that one is impressive).

Now I can try to connect and check what new memory-related settings and tables are available (note that I had to log in as OS user who started the server, as Unix socket authentication plugin is installed and used by default for by default):

openxs@ao756:~/dbs/maria10.5$ bin/mysql --socket=/tmp/mariadb.sock test
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 7
Server version: 10.5.5-MariaDB Source distribution

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [test]> show grants;
+-------------------------------------------------------------------------------------------------------------------------------------------+
| Grants for openxs@localhost                                                                                                               |
+-------------------------------------------------------------------------------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO `openxs`@`localhost` IDENTIFIED VIA mysql_native_password USING 'invalid' OR unix_socket WITH GRANT OPTION |
+-------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0,000 sec)

MariaDB [test]> select table_name from information_schema.tables where table_schema='performance_schema' and table_name like 'memory%';
+-----------------------------------------+
| table_name                              |
+-----------------------------------------+
| memory_summary_by_account_by_event_name |
| memory_summary_by_host_by_event_name    |
| memory_summary_by_thread_by_event_name  |
| memory_summary_by_user_by_event_name    |
| memory_summary_global_by_event_name     |
+-----------------------------------------+
5 rows in set (0,001 sec)

MariaDB [test]> select count(*) from performance_schema.setup_instruments where name like '%memory%' and enabled='yes';
+----------+
| count(*) |
+----------+
|       70 |
+----------+
1 row in set (0,003 sec)

MariaDB [test]> select count(*) from performance_schema.setup_instruments where name like '%memory%';
+----------+
| count(*) |
+----------+
|      270 |
+----------+
1 row in set (0,003 sec)

MariaDB [test]> select * from performance_schema.setup_instruments where name like '%memory%' and enabled='yes';
+--------------------------------------------------------------------------------+---------+-------+
| NAME                                                                           | ENABLED | TIMED |
+--------------------------------------------------------------------------------+---------+-------+
| memory/performance_schema/mutex_instances                                      | YES     | NO    |
| memory/performance_schema/rwlock_instances                                     | YES     | NO    |
...
| memory/performance_schema/prepared_statements_instances                        | YES     | NO    |
| memory/performance_schema/scalable_buffer                                      | YES     | NO    |
+--------------------------------------------------------------------------------+---------+-------+
70 rows in set (0,003 sec)

We have the expected 5 summary tables and some 270(!)  new instruments, of then 70 related to performance_schema itself are enabled by default. Note that MySQL 5.7.30, for example, has more memory instruments:

openxs@ao756:~/dbs/5.7$ bin/mysql -uroot --socket=/tmp/mysql57.sock -e"select version(), count(*) from performance_schema.setup_instruments where name like 'memory%'"
+-----------+----------+
| version() | count(*) |
+-----------+----------+
| 5.7.30    |      376 |
+-----------+----------+

 We can check InnoDB memory instrumentation and then enable everything for a quick test:

MariaDB [test]> select * from performance_schema.setup_instruments where name like '%memory%innodb%';
+-------------------------------------------+---------+-------+
| NAME                                      | ENABLED | TIMED |
+-------------------------------------------+---------+-------+
| memory/innodb/adaptive hash index         | NO      | NO    |
| memory/innodb/buf_buf_pool                | NO      | NO    |
| memory/innodb/dict_stats_bg_recalc_pool_t | NO      | NO    |
| memory/innodb/dict_stats_index_map_t      | NO      | NO    |
| memory/innodb/dict_stats_n_diff_on_level  | NO      | NO    |
| memory/innodb/other                       | NO      | NO    |
...
| memory/innodb/ut0mem                      | NO      | NO    |
| memory/innodb/ut0new                      | NO      | NO    |
| memory/innodb/ut0pool                     | NO      | NO    |
| memory/innodb/ut0rbt                      | NO      | NO    |
| memory/innodb/ut0wqueue                   | NO      | NO    |
| memory/innodb/xtrabackup                  | NO      | NO    |
+-------------------------------------------+---------+-------+
72 rows in set (0,003 sec)

MariaDB [test]> update performance_schema.setup_instruments set enabled = 'yes', timed = 'yes' where name like '%memory%';
Query OK, 270 rows affected (0,003 sec)
Rows matched: 270  Changed: 270  Warnings: 0

My main initial source of information is this table, summartising memory usage globally:

MariaDB [test]> desc performance_schema.memory_summary_global_by_event_name;
+------------------------------+---------------------+------+-----+---------+-------+
| Field                        | Type                | Null | Key | Default | Extra |
+------------------------------+---------------------+------+-----+---------+-------+
| EVENT_NAME                   | varchar(128)        | NO   |     | NULL    |       |
| COUNT_ALLOC                  | bigint(20) unsigned | NO   |     | NULL    |       |
| COUNT_FREE                   | bigint(20) unsigned | NO   |     | NULL    |       |
| SUM_NUMBER_OF_BYTES_ALLOC    | bigint(20) unsigned | NO   |     | NULL    |       |
| SUM_NUMBER_OF_BYTES_FREE     | bigint(20) unsigned | NO   |     | NULL    |       |
| LOW_COUNT_USED               | bigint(20)          | NO   |     | NULL    |       |
| CURRENT_COUNT_USED           | bigint(20)          | NO   |     | NULL    |       |
| HIGH_COUNT_USED              | bigint(20)          | NO   |     | NULL    |       |
| LOW_NUMBER_OF_BYTES_USED     | bigint(20)          | NO   |     | NULL    |       |
| CURRENT_NUMBER_OF_BYTES_USED | bigint(20)          | NO   |     | NULL    |       |
| HIGH_NUMBER_OF_BYTES_USED    | bigint(20)          | NO   |     | NULL    |       |
+------------------------------+---------------------+------+-----+---------+-------+
11 rows in set (0,002 sec)

MariaDB [test]> select event_name,
    ->        sum_number_of_bytes_alloc,
    ->        high_number_of_bytes_used
    -> from
    ->   performance_schema.memory_summary_global_by_event_name
    -> where current_count_used > 0
    -> order by 2 desc;
+--------------------------------------------------------------------------------+---------------------------+---------------------------+
| event_name                                                                     | sum_number_of_bytes_alloc | high_number_of_bytes_used |
+--------------------------------------------------------------------------------+---------------------------+---------------------------+
| memory/performance_schema/events_statements_summary_by_thread_by_event_name    |                  10457088 |                  10457088 |
| memory/performance_schema/memory_summary_by_thread_by_event_name               |                   5898240 |                   5898240 |
| memory/performance_schema/events_statements_summary_by_user_by_event_name      |                   5228544 |                   5228544 |
| memory/performance_schema/events_statements_summary_by_host_by_event_name      |                   5228544 |                   5228544 |
...
| memory/sql/dboptions_hash                                                      |                      1088 |                      1088 |
| memory/sql/user_var_entry                                                      |                       512 |                       512 |
| memory/sql/THD::db                                                             |                         8 |                         8 |
| memory/sql/MPVIO_EXT::auth_info                                                |                         8 |                         8 |
+--------------------------------------------------------------------------------+---------------------------+---------------------------+
71 rows in set (0,002 sec)

Obviously memory is mostly used for the Performanc e Schema itself so far. Now let's run some sysbench test and check what memory usage is reported after it:

openxs@ao756:~/dbs/maria10.5$ sysbench --table-size=1000000 --threads=1 --mysql-socket=/tmp/mariadb.sock --mysql-user=openxs --mysql-db=sbtest /usr/share/sysbench/oltp_read_only.lua prepare
sysbench 1.1.0-faaff4f (using bundled LuaJIT 2.1.0-beta3)

Creating table 'sbtest1'...
Inserting 1000000 records into 'sbtest1'
Creating a secondary index on 'sbtest1'...
openxs@ao756:~/dbs/maria10.5$ sysbench --table-size=1000000 --threads=4 --time=30 --interval=2 --mysql-socket=/tmp/mariadb.sock --mysql-user=openxs --mysql-db=sbtest /usr/share/sysbench/oltp_read_only.lua run
sysbench 1.1.0-faaff4f (using bundled LuaJIT 2.1.0-beta3)
...
[ 2s ] thds: 4 tps: 588.22 qps: 9423.03 (r/w/o: 8244.59/0.00/1178.44) lat (ms,95%): 9.39 err/s: 0.00 reconn/s: 0.00
[ 4s ] thds: 4 tps: 629.50 qps: 10081.05 (r/w/o: 8822.04/0.00/1259.01) lat (ms,95%): 9.06 err/s: 0.00 reconn/s: 0.00
[ 6s ] thds: 4 tps: 604.08 qps: 9672.34 (r/w/o: 8464.17/0.00/1208.17) lat (ms,95%): 8.74 err/s: 0.00 reconn/s: 0.00
[ 8s ] thds: 4 tps: 617.97 qps: 9882.99 (r/w/o: 8647.05/0.00/1235.94) lat (ms,95%): 9.22 err/s: 0.00 reconn/s: 0.00
...

After the test is completed I tried the following query:

MariaDB [test]> select event_name, high_number_of_bytes_used from performance_schema.memory_summary_global_by_event_name where event_name not like '%performance_schema%' order by 2 desc limit 10;
                                            
+----------------------------------------------+---------------------------+
| event_name                                   | high_number_of_bytes_used |
+----------------------------------------------+---------------------------+
| memory/innodb/mem0mem                        |                   9377611 |
| memory/sql/thd::main_mem_root                |                   4286600 |
| memory/innodb/row_merge_sort                 |                   3145728 |
| memory/innodb/row0merge                      |                   2097316 |
| memory/memory/HP_PTRS                        |                   1016352 |
| memory/sql/Prepared_statement::main_mem_root |                    590400 |
| memory/sql/TABLE                             |                    525608 |
| memory/innodb/std                            |                    399192 |
| memory/innodb/row0log                        |                    131474 |
| memory/sql/TABLE_SHARE::mem_root             |                     42272 |
+----------------------------------------------+---------------------------+
10 rows in set (0,003 sec)

The result was surprising to me, as I do not sdee thye InnoDB buffer pool memory usage above. But this is yet another case of Performance Schema instrument that is NOT dynamic. I've reported a bug about these years ago, see Bug #68097 - "Manual does not explain that some P_S instruments must be enabled at startup".

So, I restarted with all memory instruments enabled and reppeated the test:

MariaDB [test]> shutdown;
Query OK, 0 rows affected (0,001 sec)

MariaDB [test]> exit
Bye
[1]+  Done                    bin/mysqld_safe --no-defaults --port=3309 --socket=/tmp/mariadb.sock --performance_schema=ON

openxs@ao756:~/dbs/maria10.5$ bin/mysqld_safe --no-defaults --port=3309 --socket=/tmp/mariadb.sock --performance_schema=ON --performance-schema-instrument='memory/%=ON' &
[1] 29502
openxs@ao756:~/dbs/maria10.5$ 200809 14:53:59 mysqld_safe Logging to '/home/openxs/dbs/maria10.5/data/ao756.err'.
200809 14:53:59 mysqld_safe Starting mariadbd daemon with databases from /home/openxs/dbs/maria10.5/data

openxs@ao756:~/dbs/maria10.5$ bin/mysql --socket=/tmp/mariadb.sock -e"select count(*) from performance_schema.setup_instruments where name like 'memory%' and enabled='yes'"
+----------+
| count(*) |
+----------+
|      270 |
+----------+

openxs@ao756:~/dbs/maria10.5$ sysbench --table-size=1000000 --threads=4 --time=30 --report-interval=2 --mysql-socket=/tmp/mariadb.sock --mysql-user=openxs --mysql-db=sbtest /usr/share/sysbench/oltp_read_only.lua run
sysbench 1.1.0-faaff4f (using bundled LuaJIT 2.1.0-beta3)

Running the test with following options:
Number of threads: 4
Report intermediate results every 2 second(s)
Initializing random number generator from current time


Initializing worker threads...

Threads started!

[ 2s ] thds: 4 tps: 606.19 qps: 9715.08 (r/w/o: 8500.70/0.00/1214.39) lat (ms,95%): 10.46 err/s: 0.00 reconn/s: 0.00
[ 4s ] thds: 4 tps: 641.03 qps: 10262.98 (r/w/o: 8980.92/0.00/1282.06) lat (ms,95%): 6.67 err/s: 0.00 reconn/s: 0.00
...

openxs@ao756:~/dbs/maria10.5$ bin/mysql --socket=/tmp/mariadb.sock test
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 9
Server version: 10.5.5-MariaDB Source distribution

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [test]> select event_name, high_number_of_bytes_used from performance_schema.memory_summary_global_by_event_name where event_name not like '%performance_schema%' and high_number_of_bytes_used > 0 order by 2 desc;
+----------------------------------------------+---------------------------+
| event_name                                   | high_number_of_bytes_used |
+----------------------------------------------+---------------------------+
| memory/innodb/buf_buf_pool                   |                 134217728 |
| memory/sql/XID                               |                  19922944 |
| memory/innodb/ut0pool                        |                   4194480 |
| memory/innodb/hash0hash                      |                   2484000 |
| memory/innodb/os0event                       |                   2120064 |
| memory/memory/HP_PTRS                        |                   1016352 |
| memory/sql/Prepared_statement::main_mem_root |                    590400 |
| memory/sql/TABLE                             |                    351264 |
...
| memory/sql/MDL_context::acquire_locks        |                        16 |
| memory/sql/NAMED_ILINK::name                 |                        16 |
| memory/sql/ignored_db                        |                         8 |
+----------------------------------------------+---------------------------+
70 rows in set (0,003 sec)

Now to line in the outut is exactly the one I've expected. As for the rest, some would require additional efforts to find out what this memory is used for. In conclusion I'd like to use a nice query from this useful blog post to summarise memory usage per "subsystem":

MariaDB [test]> select substring_index(substring_index(event_name, '/', 2), '/', -1) as event_type,
    -> round(sum(CURRENT_NUMBER_OF_BYTES_USED)/1024/1024, 2) as MB_CURRENTLY_USED
    -> from performance_schema.memory_summary_global_by_event_name
    -> group by event_type
    -> having MB_CURRENTLY_USED>0;
+--------------------+-------------------+
| event_type         | MB_CURRENTLY_USED |
+--------------------+-------------------+
| innodb             |            136.95 |
| memory             |              0.21 |
| performance_schema |            104.06 |
| sql                |              0.71 |
+--------------------+-------------------+
4 rows in set (0,003 sec)

Basically, with all instrumentation enabled you can now use Performance Schema in MariaDB 10.5 to find and study memory usdage and leaks, same as in MySQL 5.7+.

Let's check the harvest, what was grown up under the name of MariaDB 10.5 GA...

To summarize:

• MariaDB 10.5 is real, you can build it from GitHub source and it works, including new features memory monitoring tables in Performance Schema. Just make sure to properly enable the instrumentation at startup.
• The public documentation at the moment is very limited or does not exist, so we have to rely on fine MySQL manual (that also misses too many details) etc. I've created this task asking to add documentation for memory* (or all) instruments.
  
• It's yet to be checked if any known related Performance Schema bugs in MySQL are inherited by MariaDB 10.5.
• It's yet to be determined what memory instruments from recent MySQL 5.7.x are missing in recent MariaDB 10.5.x and what are added, and why. Looks like many from the check below:

openxs@ao756:~/dbs/5.7$ bin/mysql -uroot --socket=/tmp/mysql57.sock -e"select name from performance_schema.setup_instruments where name like 'memory%' order by name" > /tmp/mysql57.txt
openxs@ao756:~/dbs/5.7$ bin/mysql --socket=/tmp/mariadb.sock -e"select name from performance_schema.setup_instruments where name like 'memory%' order by name" > /tmp/mariadb.txt
openxs@ao756:~/dbs/5.7$ diff -u /tmp/mysql57.txt /tmp/mariadb.txt > /tmp/ps_memory.txt
openxs@ao756:~/dbs/5.7$ more /tmp/ps_memory.txt
--- /tmp/mysql57.txt    2020-08-09 17:30:27.199204590 +0300
+++ /tmp/mariadb.txt    2020-08-09 17:30:31.459270994 +0300
@@ -1,22 +1,12 @@
 name
-memory/archive/FRM
-memory/archive/record_buffer
-memory/blackhole/blackhole_share
-memory/client/MYSQL
-memory/client/MYSQL_DATA
-memory/client/MYSQL_HANDSHAKE
-memory/client/mysql_options
-memory/client/MYSQL_RES
-memory/client/MYSQL_ROW
-memory/client/MYSQL_STATE_CHANGE_INFO
 memory/csv/blobroot
 memory/csv/row
 memory/csv/tina_set
 memory/csv/TINA_SHARE
 memory/csv/Transparent_file
 memory/innodb/adaptive hash index
-memory/innodb/api0api
 memory/innodb/btr0btr
+memory/innodb/btr0buf
...
openxs@ao756:~/dbs/5.7$ cat /tmp/ps_memory.txt | grep '^+'
+++ /tmp/mariadb.txt    2020-08-09 17:30:31.459270994 +0300
+memory/innodb/btr0buf
+memory/innodb/fil0crypt
+memory/innodb/fts0blex
+memory/innodb/fts0file
+memory/innodb/fts0tlex
+memory/innodb/sync0start
+memory/innodb/trx0seg
+memory/innodb/ut0new
+memory/innodb/xtrabackup
+memory/partition/Partition_admin
+memory/partition/Partition_share
+memory/partition/partition_sort_buffer
openxs@ao756:~/dbs/5.7$

So, stay tuned! More blog posts on MariaDB 10.5 Performance Schema improvements are to be expected.

Dynamic Tracing of C++ Class Member Functions with perf

I've started to write posts about dynamic tracing on Linux last year, and basic examples presented here and there make it look like in general with perf it's already easy to add dynamic probe for entry and return for any function, or even for every other line  of code inside the function (that perf probe -x <path to binary> --line <function name> shows). Numerous examples of adding probes to do_command(), dispatch_command() in MySQL or MariaDB code (or even malloc() provided by the libraries) etc kind of illustrated if not proved that.

It turned out that when one tries to use this method in a more generic case against MySQL or MariaDB code things may get way more complicated. The reason is that the code these days is mostly C++ and one often has to trace class member functions, not just plain global C functions. The problem can be easily demonstrated this way:

openxs@ao756:~/dbs/maria10.3$ ps aux | grep dbs
openxs   30377  0.8  3.2 1849476 125008 pts/18 Sl   14:03   0:00 /home/openxs/dbs/maria10.3/bin/mysqld --no-defaults --basedir=/home/openxs/dbs/maria10.3 --datadir=/home/openxs/dbs/maria10.3/data --plugin-dir=/home/openxs/dbs/maria10.3/lib/plugin --log-error=/home/openxs/dbs/maria10.3/data/ao756.err --pid-file=ao756.pid --socket=/tmp/mariadb.sock --port=3309
...
openxs@ao756:~$ perf version
perf version 4.4.219

So, I have a nice MariaDB 10.3.x server built from GitHub source as usual, up and running on my netbook/"bedroom test server" with Ubuntu 16.04.6 LTS (GNU/Linux 4.4.0-179-generic x86_64). Let's assume I want to add a probe to some method that I clearly see and can use in gdb, like this:

openxs@ao756:~/dbs/maria10.3$ sudo gdb -p 30377
GNU gdb (Ubuntu 7.11.1-0ubuntu1~16.5) 7.11.1
...
[New LWP 30447]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
0x00007fd8b1b1f80d in poll () at ../sysdeps/unix/syscall-template.S:84
84      ../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) b ha_heap::records_in_range
Breakpoint 1 at 0x55f7d3aeccf0: file /home/openxs/git/server/storage/heap/ha_heap.cc, line 586.
(gdb)

So, gdb kindly understands method names and one may expect the same from perf. Now if I quit gdb and try to add probe:

openxs@ao756:~/dbs/maria10.3$ perf probe -x /home/openxs/dbs/maria10.3/bin/mysqld ha_heap::records_in_range
Semantic error :There is non-digit char in line number.
  Error: Command Parse Error.
openxs@ao756:~/dbs/maria10.3$

The reason is that perf probe syntax

PROBE SYNTAX
       Probe points are defined by following syntax.

           1) Define event based on function name
            [EVENT=]FUNC[@SRC][:RLN|+OFFS|%return|;PTN] [ARG ...]

           2) Define event based on source file with line number
            [EVENT=]SRC:ALN [ARG ...]

           3) Define event based on source file with lazy pattern
            [EVENT=]SRC;PTN [ARG ...]
...

uses the : character for line numbers, and this conflicts with the C++ scope syntax. It could probably infer that :: is not a line number, but nobody has written that yet, as of version 4.4.219.

Let's try to find out if there is still a way to add the probe. First, let's check if perf sees any similar functions, using the --funcs option:

openxs@ao756:~/dbs/maria10.3$ perf probe -x /home/openxs/dbs/maria10.3/bin/mysqld --funcs | grep records_in_range
ha_heap::records_in_range
ha_innobase::records_in_range
ha_maria::records_in_range
ha_myisam::records_in_range
ha_myisammrg::records_in_range
ha_partition::records_in_range
ha_seq::records_in_range
handler::records_in_range
hp_rb_records_in_range
maria_records_in_range
mi_records_in_range
myrg_records_in_range
openxs@ao756:~/dbs/maria10.3$ perf probe -x /home/openxs/dbs/maria10.3/bin/mysqld --funcs --no-demangle | grep records_in_range
hp_rb_records_in_range
maria_records_in_range
mi_records_in_range
myrg_records_in_range
openxs@ao756:~/dbs/maria10.3$

In theory --no-demangle means that demangling is disabled:

       --demangle
           Demangle application symbols. --no-demangle is also available for
           disabling demangling.

and I expected to see the original mangled name to refer to. But I see demangled name as one of functions I can use (while I can NOT), but do not see mangled name at all. This looks inconsistent and would be really unfortunate if true. I am sure the function exists and is visible. Quick search in Google gave a hint in this nice post, there is a filter that disables showing names starting with '_' by default:

--filter=FILTER

(Only for --vars and --funcs) Set filter. FILTER is a combination of glob pattern, see FILTER PATTERN for detail. Default FILTER is "!k???tab_* & !crc_*" for --vars, and "!_*" for --funcs. If several filters are specified, only the last filter is used.

So, let's try non-default filter:

openxs@ao756:~/dbs/maria10.3$ perf probe -x /home/openxs/dbs/maria10.3/bin/mysqld --funcs --no-demangle --filter '*' | grep records_in_range
_ZN11ha_innobase16records_in_rangeEjP12st_key_rangeS1_
_ZN12ha_myisammrg16records_in_rangeEjP12st_key_rangeS1_
_ZN12ha_partition16records_in_rangeEjP12st_key_rangeS1_
_ZN6ha_seq16records_in_rangeEjP12st_key_rangeS1_
_ZN7ha_heap16records_in_rangeEjP12st_key_rangeS1_
_ZN7handler16records_in_rangeEjP12st_key_rangeS1_
_ZN8ha_maria16records_in_rangeEjP12st_key_rangeS1_
_ZN9ha_myisam16records_in_rangeEjP12st_key_rangeS1_
hp_rb_records_in_range
maria_records_in_range
mi_records_in_range
myrg_records_in_range
openxs@ao756:~/dbs/maria10.3$

The mangles name we are looking for is _ZN7ha_heap16records_in_rangeEjP12st_key_rangeS1_. I'd expect it should work, as we had to use mangled names even for functions that are not members of any class with ftrace. So, let's try (I need sudo on Ubuntu for adding probe to work):

openxs@ao756:~/dbs/maria10.3$ sudo perf probe -x /home/openxs/dbs/maria10.3/bin/mysqld _ZN7ha_heap16records_in_rangeEjP12st_key_rangeS1_
[sudo] password for openxs:
Probe point '_ZN7ha_heap16records_in_rangeEjP12st_key_rangeS1_' not found.
  Error: Failed to add events.
openxs@ao756:~/dbs/maria10.3$ sudo perf probe --no-demangle -x /home/openxs/dbs/maria10.3/bin/mysqld _ZN7ha_heap16records_in_rangeEjP12st_key_rangeS1_
Added new event:
  probe_mysqld:_ZN7ha_heap16records_in_rangeEjP12st_key_rangeS1_ (on _ZN7ha_heap16records_in_rangeEjP12st_key_rangeS1_ in /home/openxs/dbs/maria10.3/bin/mysqld)

You can now use it in all perf tools, such as:

        perf record -e probe_mysqld:_ZN7ha_heap16records_in_rangeEjP12st_key_rangeS1_ -aR sleep 1

openxs@ao756:~/dbs/maria10.3$

As you can see, adding the mangled function name and --no-demangle option worked. I can add a probe at function exit to print the returned value as well:

openxs@ao756:~/dbs/maria10.3$ sudo perf probe --no-demangle -x /home/openxs/dbs/maria10.3/bin/mysqld --add ha_heap_records_in_range_ret='_ZN7ha_heap16records_in_rangeEjP12st_key_rangeS1_%return records=$retval:u32'
Added new event:
  probe_mysqld:ha_heap_records_in_range_ret (on _ZN7ha_heap16records_in_rangeEjP12st_key_rangeS1_%return in /home/openxs/dbs/maria10.3/bin/mysqld with records=$retval:u32)

You can now use it in all perf tools, such as:

        perf record -e probe_mysqld:ha_heap_records_in_range_ret -aR sleep 1

openxs@ao756:~/dbs/maria10.3$

As you can see I had to give an explicit another name to the exit probe and I tried to see the return value. I also had to find out what data type should be used for the return value (it's ulong or u32 in perms of perf/ftrace, see the source code). My perf is not smart enough to infer this.

Now if I try to record the probe:

openxs@ao756:~/dbs/maria10.3$ sudo perf record -e probe_mysqld:ha_heap_records_in_range_ret -aR sleep 1000
^C[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.904 MB perf.data (2 samples) ]

openxs@ao756:~/dbs/maria10.3$

while doing something with MEMORY table in another session:

openxs@ao756:~/dbs/maria10.3$ bin/mysql -uroot --socket=/tmp/mariadb.sock test
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 9
Server version: 10.3.24-MariaDB Source distribution

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [test]> show create table theap\G
*************************** 1. row ***************************
       Table: theap
Create Table: CREATE TABLE `theap` (
  `id` int(11) DEFAULT NULL,
  `c1` int(11) DEFAULT NULL,
  KEY `id` (`id`),
  KEY `c1` (`c1`) USING BTREE
) ENGINE=MEMORY DEFAULT CHARSET=latin1
1 row in set (0,000 sec)

MariaDB [test]> select * from theap;
+------+------+
| id   | c1   |
+------+------+
|    1 |    1 |
|    2 |    2 |
|    3 |    3 |
+------+------+
3 rows in set (0,001 sec)

MariaDB [test]> explain select * from theap where c1 between 2 and 3;
+------+-------------+-------+-------+---------------+------+---------+------+------+-------------+
| id   | select_type | table | type  | possible_keys | key  | key_len | ref  | rows | Extra       |
+------+-------------+-------+-------+---------------+------+---------+------+------+-------------+
|    1 | SIMPLE      | theap | range | c1            | c1   | 5       | NULL |    1 | Using where |
+------+-------------+-------+-------+---------------+------+---------+------+------+-------------+
1 row in set (0,001 sec)

MariaDB [test]> select * from theap where c1 between 2 and 3;
+------+------+
| id   | c1   |
+------+------+
|    2 |    2 |
|    3 |    3 |
+------+------+
2 rows in set (0,001 sec)

I can see that it worked:

openxs@ao756:~/dbs/maria10.3$ sudo perf script > /tmp/trace.txt
openxs@ao756:~/dbs/maria10.3$ cat /tmp/trace.txt          mysqld 31547 [001] 326219.193101: probe_mysqld:ha_heap_records_in_range_ret: (55f7d3aeccf0 <- 55f7d35df8da) records=0x1
          mysqld 31547 [001] 326224.706375: probe_mysqld:ha_heap_records_in_range_ret: (55f7d3aeccf0 <- 55f7d35df8da) records=0x1
openxs@ao756:~/dbs/maria10.3$

It works as expected! You may want to find out why it returned the value we see (1 in hex) etc, but basically it works,

Never give up! I want Sam to be remembered for this attitude...

To summarize:

1. Never give up on dynamic tracing, it works!
2. With your version of perf you may have to use mangled names for C++ class member functions and --no-demangle option to define the probe.
3. You may have to quote the probe while adding, if it has some special characters like ':'. Read the man perf-probe manual carefully also.
4. You may have to study the source code to print the arguments or return values properly.
5. There are other options to deal with C++ class memeber functions. You can refer to them by source file and line number, or even by address that you find in objdump etc.
6. I hope one day tools like bpftrace will let us use the real, not mangled names of functions. I have to check on Fedora 31 if it's already the case.
7. I feel myself cool when some experienced developer asks me something about perf and I can provide an answer, even if not immediately :)

Fun with Bugs #100 - On MySQL Bug Reports I am Subscribed to, Part XXXIV

I delayed this post #100 in the "Fun with Bugs" series for few weeks - the previous one was published 4 weeks ago. The idea was to make it the last one, and for this I needed something to celebrate. Two days ago proper event happened, we have MySQL Bug #100000 reported! Here it is:

• Bug #100000 - "Provide an index hint that only affects the choice of index for NL join". This nice feature request was added by former optimizer developer in MySQL, Øystein Grøvlen. Hundreds of other feature requests are waiting for the attention both from the MySQL Verification Team and from developers, so good to see a feature request getting the number that nobody ever forget!

Actually Øystein Grøvlen created several interesting bug report during that day:

• Bug #99994 - "Index range scan is chosen where table scan takes 40% less time". Clear and simple bug report that relies on the world sample database.
• Bug #99995 - "Histogram is not used for filtering estimate when index is disabled".
• Bug #99996 - "Prefer histogram over index statistics when eq_range_index_dive_limit is exceeded". This was verified as a feature request.
• Bug #99997 - "Range estimates are usually off by a factor of 2 for large ranges". It was declared a duplicate of older bug report I am also subscribed to, Bug #73386 - "For ranges, innodb doubles estimates, or caps estimates to half the table". See also this MariaDB bug report, MDEV-19424 - "InnoDB's records_in_range estimates are capped at about 50%", and links from it for a lot of related discussions. Let's wait and see what vendor resolves this faster...
  The other report, Bug #99998 - "For large ranges, the range estimate will never exceed 50%", is probably also a duplicate of the same old bug.
• Bug #99999 - "EXPLAIN FORMAT=TREE does not show cost/rows for semijoin materialization". Yet another nice and clear bug report.

So, hardly anyone else had a chance to get that #100000 filed. As far as I can see, all these were reported during a very short period of 2 minutes, from "26 Jun 7:57" till "26 Jun 7:58"! Not sure how to do this without some automation or at least all the details ready for quick copy/pasting!

Now back to some older bugs I've subscribed to over last 4 weeks:

• Bug #99791 - "MySQL 8 orphaned table due to unchecked non-existent row format check." As reported by Marc Reilly, tables created in versions < MySQL 8 which use row_format COMPRESSED or REDUNDANT, where row_format is not set explicitly in the Table DDL allow users to create un-prefixed indexes on fields which exceed the maximum column size of 767 bytes. Upgrading to MySQL 8 do nothing with these tables, but as soon as new index is added and reboot happens, such a table becomes inaccessible. What a surprise!
• Bug #99794 - "MySQL 57 client is inefficient at bulkloads/binlog replay". In this bug report  Marc Reilly basically asks to back port the fix from MySQL 8.0.13.
• Bug #99800 - "ps_truncate_all_tables() does not work in super_read_only mode". This regression bug was reported by Lalit Choudhary.
• Bug #99805 - "mysql async client is incomplete". There is no way to determine file descriptor state (should it block on read or write), so it is impossible to use it in asynchronous contexts without busy looping. This bug report by Domas Mituzas was used in one discussion as an argument that MySQL bugs database still gets proper attention from MySQL engineers. It's truly so.
• Bug #99892 - "initialize with innodb_page_size=4096 gets "Specified key was too long" errors". This is a regression vs 5.7 (without a tag). As Mark Callaghan found out, one can not initialize MySQL 8 instance without errors with such a small innodb_page_size.
• Bug #99924 - "The record per key value from InnoDB is not suitable when n_diff is zero". As reported by Ze Yang, due to lack of locking when server reads the innodb_rec_per_key, the n_diff value may be 0 (not set) while the table->stat_n_rows is > 0. As a result (see great comment by Øystein Grøvlen), if a table object is opened during the recalculation of statistics, the rec_per_key for a column/index may be quite misleading. It will be interpreted as all rows have the same value, and the index will probably not be chosen for any non-covering scans. There is a patch suggested (to set rec_per_key to 1 or 10 in such case), as well as other suggestion to set the value REC_PER_KEY_UNKNOWN. Useful reading!
• Bug #99933  - "In-memory hash join will only use two-thirds of join buffer". Yet another bug report related to hash joins from Øystein Grøvlen, with a fix suggested. See also his Bug #99934 - "Hash join adds columns to the hash table that is not needed." There is a lot of work ahead to improve the implementation of this new feature in MySQL 8.
• Bug #99935 - "innodb_doublewrite_files is not correct when innodb_buffer_pool_size > 1G". Just 2 files are created instead of 16 according to the manual. This bug was reported by Satya Bodapati.
• Bug #99943 - "Hash join does not work for Semijoin and Antijoin". This bug report from Tibor Korocz was "Verified", but later comments suggest that it's more like wrong expectations/interpretation of cases when the feature has to be used (it is supposed to be used instead of BNL, but not instead of semijoin materialization and subquery materialization). Let's wait and see how it ends up...
• Bug #99966 - "Switching to use NUMA-SMART Counter for statistical counters". Great bug report from Krunal Bauskar, with a patch suggested. I hope to get a NUMA system one day myself to understand the challenges and performance problems there better.  

So, that's it, my very last post in the "Fun with Bugs" series that started more than 7 years ago. The series where I listed most of the interesting bug reports I keep an eye on, since Bug #2. It was a long way with a lot of fun and a lot of (rarely appreciated) work in the process, but now my watch has ended. I am not going to try to micro manage MySQL bugs processing any more and finally let the MySQL Verification Team do their job without my regular attention. Good luck!

Percona had recently started to blog about bugs, so I am sure they will keep an eye and share lists of important bugs on a regular basis. They should really care more than I do these days.

The Magic Behind the innodb_dedicated_server=ON

Two days ago I noted this tweet by Mark Callaghan:

"This month I learned that innodb_dedicated_server is great. Don't need to set many options beyond it. I have been doing it wrong."

and decided to check what this great setting (that I also never cared to use with MySQL 8) is really doing. I could, surely, just re-read the fine manual (and I did that), but what can be better than just trying it?

Yesterday I had some free time in the morning for testing random things and was sitting near my good old Fedora (yes, I know, time to use 32 if not 33...) test box, with 8G of RAM and 4 cores:

[openxs@fc29 8.0]$ pt-summary

# Percona Toolkit System Summary Report ######################

        Date | 2020-06-20 05:27:35 UTC (local TZ: EEST +0300)

    Hostname | fc29

      Uptime | 39 min,  1 user,  load average: 0.29, 0.37, 0.39

    Platform | Linux

     Release | Fedora release 29 (Twenty Nine)

      Kernel | 5.3.11-100.fc29.x86_64

Architecture | CPU = 64-bit, OS = 64-bit

   Threading | NPTL 2.28

    Compiler | GNU CC version 8.3.1 20190223 (Red Hat 8.3.1-2).

     SELinux | Enforcing

 Virtualized | No virtualization detected

# Processor ##################################################

  Processors | physical = 1, cores = 4, virtual = 4, hyperthreading = no

      Speeds | 1x1999.777, 1x1999.816, 1x2001.216, 1x2030.647

      Models | 4xIntel(R) Core(TM)2 Quad CPU Q8300 @ 2.50GHz

      Caches | 4x2048 KB

# Memory #####################################################

       Total | 7.7G

        Free | 247.4M

        Used | physical = 2.1G, swap allocated = 0.0, swap used = 0.0, virtual = 2.1G

      Shared | 198.6M

     Buffers | 5.4G

      Caches | 5.1G

       Dirty | 352 kB

     UsedRSS | 4.3G

  Swappiness | 60

 DirtyPolicy | 20, 10

 DirtyStatus | 0, 0

...

and it had MySQL 8.0.18 there (also time to rebuild from recent GitHub source, I know...). So, I tried to compare settings with --no-defaults:

[openxs@fc29 8.0]$ ./bin/mysqld_safe --no-defaults --basedir=/home/openxs/dbs/8.0 --datadir=/home/openxs/dbs/8.0/data &

[1] 3764

[openxs@fc29 8.0]$ 2020-06-20T05:21:24.289203Z mysqld_safe Logging to '/home/openxs/dbs/8.0/data/fc29.err'.

2020-06-20T05:21:24.378630Z mysqld_safe Starting mysqld daemon with databases from /home/openxs/dbs/8.0/data

[openxs@fc29 8.0]$ ./bin/mysql -uroot -e'select version()';

+-----------+

| version() |

+-----------+

| 8.0.18    |

+-----------+

[openxs@fc29 8.0]$ ./bin/mysql -uroot -e'show global variables' >/tmp/default.txt

[openxs@fc29 8.0]$ ./bin/mysql -uroot -e'shutdown';

[openxs@fc29 8.0]$ 2020-06-20T05:22:35.220091Z mysqld_safe mysqld from pid file /home/openxs/dbs/8.0/data/fc29.pid ended

[1]+  Done                    ./bin/mysqld_safe --no-defaults --basedir=/home/openxs/dbs/8.0 --datadir=/home/openxs/dbs/8.0/data

[openxs@fc29 8.0]$ cat /tmp/default.txt | grep innodb_dedicated

innodb_dedicated_server OFF

Then I've added the magic option and repeated the same steps:

[openxs@fc29 8.0]$ ./bin/mysqld_safe --no-defaults --basedir=/home/openxs/dbs/8.0 --datadir=/home/openxs/dbs/8.0/data --innodb_dedicated_server=ON &

[1] 3993

[openxs@fc29 8.0]$ 2020-06-20T05:23:10.824899Z mysqld_safe Logging to '/home/openxs/dbs/8.0/data/fc29.err'.

2020-06-20T05:23:10.870749Z mysqld_safe Starting mysqld daemon with databases from /home/openxs/dbs/8.0/data

[openxs@fc29 8.0]$ tail -f data/fc29.err 

2020-06-20T05:23:10.870749Z mysqld_safe Starting mysqld daemon with databases from /home/openxs/dbs/8.0/data

2020-06-20T05:23:10.888077Z 0 [Warning] [MY-010139] [Server] Changed limits: max_open_files: 1024 (requested 8161)

2020-06-20T05:23:10.888097Z 0 [Warning] [MY-010142] [Server] Changed limits: table_open_cache: 431 (requested 4000)

2020-06-20T05:23:11.168384Z 0 [System] [MY-010116] [Server] /home/openxs/dbs/8.0/bin/mysqld (mysqld 8.0.18) starting as process 4117

 100 200 300 400 500

 100 200 300 400 500

 100 200 300 400 500

 100 200 300 400 500

 100 200 300 400 500

 100 200 300 400 500

2020-06-20T05:23:59.904782Z 0 [Warning] [MY-010068] [Server] CA certificate ca.pem is self signed.

2020-06-20T05:24:00.145885Z 0 [System] [MY-010931] [Server] /home/openxs/dbs/8.0/bin/mysqld: ready for connections. Version: '8.0.18'  socket: '/tmp/mysql.sock'  port: 3306  Source distribution.

2020-06-20T05:24:00.218482Z 0 [System] [MY-011323] [Server] X Plugin ready for connections. Socket: '/tmp/mysqlx.sock' bind-address: '::' port: 33060

^C

[openxs@fc29 8.0]$ ./bin/mysql -uroot -e'show global variables' >/tmp/dedicated.txt

So, what was the real difference? Here it is, thanks diff:

[openxs@fc29 8.0]$ diff -u /tmp/default.txt /tmp/dedicated.txt 

--- /tmp/default.txt    2020-06-20 08:22:25.674368791 +0300

+++ /tmp/dedicated.txt  2020-06-20 08:24:40.938561950 +0300

@@ -130,11 +130,11 @@

 innodb_buffer_pool_dump_pct    25

 innodb_buffer_pool_filename    ib_buffer_pool

 innodb_buffer_pool_in_core_file    ON

-innodb_buffer_pool_instances   1

+innodb_buffer_pool_instances   8

 innodb_buffer_pool_load_abort  OFF

 innodb_buffer_pool_load_at_startup ON

 innodb_buffer_pool_load_now    OFF

-innodb_buffer_pool_size    134217728

+innodb_buffer_pool_size    6442450944

 innodb_change_buffer_max_size  25

 innodb_change_buffering    all

 innodb_checksum_algorithm  crc32

@@ -147,7 +147,7 @@

 innodb_data_file_path  ibdata1:12M:autoextend

 innodb_data_home_dir   

 innodb_deadlock_detect ON

-innodb_dedicated_server    OFF

+innodb_dedicated_server    ON

 innodb_default_row_format  dynamic

 innodb_directories 

 innodb_disable_sort_file_cache OFF

@@ -157,7 +157,7 @@

 innodb_fill_factor 100

 innodb_flush_log_at_timeout    1

 innodb_flush_log_at_trx_commit 1

-innodb_flush_method    fsync

+innodb_flush_method    O_DIRECT_NO_FSYNC

 innodb_flush_neighbors 0

 innodb_flush_sync  ON

 innodb_flushing_avg_loops  30

@@ -183,8 +183,8 @@

 innodb_log_buffer_size 16777216

 innodb_log_checksums   ON

 innodb_log_compressed_pages    ON

-innodb_log_file_size   50331648

-innodb_log_files_in_group  2

+innodb_log_file_size   536870912

+innodb_log_files_in_group  6

 innodb_log_group_home_dir  ./

 innodb_log_spin_cpu_abs_lwm    80

 innodb_log_spin_cpu_pct_hwm    50

@@ -205,7 +205,7 @@

 innodb_online_alter_log_max_size   134217728

 innodb_open_files  431

 innodb_optimize_fulltext_only  OFF

-innodb_page_cleaners   1

+innodb_page_cleaners   4

 innodb_page_size   16384

 innodb_parallel_read_threads   4

 innodb_print_all_deadlocks OFF

[openxs@fc29 8.0]$ 

Actually, fine manual page that Mark Callaghan pointed to, explain most of these changes:

"When innodb_dedicated_server is enabled, InnoDB automatically configures the following variables:

• innodb_buffer_pool_size
• innodb_log_file_size
• innodb_log_files_in_group (as of MySQL 8.0.14)
• innodb_flush_method

Only consider enabling innodb_dedicated_server if the MySQL instance resides on a dedicated server where it can use all available system resources."

It described the settings in details. For systems with >4G of RAM (like mine) 75% of RAM is allocated for innodb_buffer_poll_size. Then if innodb_buffer_pool_size <= 8G, innodb_log_file_size is set to 512M. Number of redo log files in group is explained properly:

"The number of log files is configured according to the automatically configured buffer pool size (in gigabytes)."

That's why we see 6G for innodb_buffer_pool_size (75% of almost 8G) and 6 for innodb_log_files_in_group. I am not sure if that many (or more than 3) log files make any practical sense or help with anything, but probably it's a way to make sure total capacity of redo log is "large enough", while each log is not larger than 2048M.

As for setting innodb_flush_method, the value of O_DIRECT_NO_FSYNC is questionable, because of a known bug, Bug #94912 - "O_DIRECT_NO_FSYNC possible write hole". The manual is clear about this case:

"Data loss is possible if redo log files and data files reside on different storage devices, and a crash occurs before data file writes are flushed from a device cache that is not battery-backed. If you use or intend to use different storage devices for redo log files and data files, and your data files reside on a device with a cache that is not battery-backed, use O_DIRECT instead."

But I am not yet sure if the implementation is smart enough NOT to make this setting when redo logs are stored on different filesystem. Something to check later.

You may ask why setting innodb_page_cleaners to 4 is  NOT documented? Well, it is the default setting and the reason why it was adjusted to 1 in my initial configuration is explained in the manual here:

"If the number of page cleaner threads exceeds the number of buffer pool instances, innodb_page_cleaners is automatically set to the same value as innodb_buffer_pool_instances. "

I had one buffer pool instance by default, as default innodb_buffer_pool_size was < 1G. As a result of this magic tuning it's 6G, so 8 instances are used (and we can use 4 innodb_page_cleaners). Again, a questionable (but default) setting.

The default value of innodb_page_cleaners, 4, is not the best fit for all. As recent Percona blog stated:

"With 4 cleaner threads, InnoDB is able to flush at a very high rate. Actually, unless you are using Percona Server for MySQL with the parallel doublewrite buffers feature, very likely the doublewrite buffer will bottleneck before the cleaner threads."

After reading the manual pages related to the feature, I found it well documented. The only formal problem was reported as Bug #99945 - "Missing details in the description of innodb_dedicated_server".

Sometimes we have to clarify the details of some MySQL features, to find out there is no real magic behind them.

To summarize:

• I would not say that innodb_dedicated_server setting replaces setting of really many options. Just 4 by the manual and 6 in my corner case that compared to --no-defaults settings.
• Some settings are obvious and good (use 75% of RAM for InnoDB buffer pool if RAM is large enough, use reasonably large redo log space, others are somewhat questionable. The company I work for moves to the opposite direction with them for version 10.5.
• The feature is well documented.
• Personally I do not think that doing one setting instead of 4-6, for key InnoDB variables, is such a big deal for any use cases besides some artificial benchmarks.