MySQL queries to some tables in information_schema kill all connections to server
It turns out there was some corrupt index.

First, I queried my server to find the log file location: show variables like 'log_error'

Then I tail -f /path/to/error_log and ran the offending query again.

It shows up in the logs like this:

2017-07-12T18:12:26.860805Z 3 [ERROR] InnoDB: Flag mismatch in page [page id: space=124998, page number=130] index `index_some_table_on_some_column` of table `some_database`.`some_table`
2017-07-12 13:12:26 0x700000d51000  InnoDB: Assertion failure in thread 123145316274176 in file btr0btr.cc line 173
InnoDB: We intentionally generate a memory trap.
InnoDB: Submit a detailed bug report to http://bugs.mysql.com.
InnoDB: If you get repeated assertion failures or crashes, even
InnoDB: immediately after the mysqld startup, there may be
InnoDB: corruption in the InnoDB tablespace. Please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.7/en/forcing-innodb-recovery.html
InnoDB: about forcing recovery.
18:12:26 UTC - mysqld got signal 6 ;
This could be because you hit a bug. It is also possible that this binary
or one of the libraries it was linked against is corrupt, improperly built,
or misconfigured. This error can also be caused by malfunctioning hardware.
Attempting to collect some information that could help diagnose the problem.
As this is a crash and something is definitely wrong, the information
collection process might fail.

key_buffer_size=402653184
read_buffer_size=2097152
max_used_connections=1
max_threads=151
thread_count=1
connection_count=1
It is possible that mysqld could use up to
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 1013751 K  bytes of memory
Hope that's ok; if not, decrease some variables in the equation.

Thread pointer: 0x7fa999103c00
Attempting backtrace. You can use the following information to find out
where mysqld died. If you see no messages after this, something went
terribly wrong...
stack_bottom = 700000d50e90 thread_stack 0x40000
0   mysqld                              0x00000001061493e7 my_print_stacktrace + 61
1   mysqld                              0x00000001060c9965 handle_fatal_signal + 690
2   libsystem_platform.dylib            0x00007fff8caff52a _sigtramp + 26
3   ???                                 0x0000700000d48820 0x0 + 123145316239392
4   libsystem_c.dylib                   0x00007fff90ebc6df abort + 129
5   mysqld                              0x000000010632df11 _Z23ut_dbg_assertion_failedPKcS0_m + 161
6   mysqld                              0x0000000106171693 _ZL22btr_root_fseg_validatePKhm + 0
7   mysqld                              0x0000000106171f86 _Z12btr_get_sizeP12dict_index_tmP5mtr_t + 51
8   mysqld                              0x00000001061d2467 _ZL24dict_stats_analyze_indexP12dict_index_t + 305
9   mysqld                              0x00000001061d41a9 _Z17dict_stats_updateP12dict_table_t23dict_stats_upd_option_t + 558
10  mysqld                              0x00000001061d45cf _Z17dict_stats_updateP12dict_table_t23dict_stats_upd_option_t + 1620
11  mysqld                              0x0000000106227518 _ZN11ha_innobase4openEPKcij + 1236
12  mysqld                              0x0000000105b89394 _ZN7handler7ha_openEP5TABLEPKcii + 48
13  mysqld                              0x000000010608dc6d _Z21open_table_from_shareP3THDP11TABLE_SHAREPKcjjjP5TABLEb + 3442
14  mysqld                              0x0000000105f9f886 _Z10open_tableP3THDP10TABLE_LISTP18Open_table_context + 3292
15  mysqld                              0x0000000105fa1c7b _Z11open_tablesP3THDPP10TABLE_LISTPjjP19Prelocking_strategy + 1185
16  mysqld                              0x0000000105fa2d9c _Z21open_tables_for_queryP3THDP10TABLE_LISTj + 69
17  mysqld                              0x000000010603a570 _ZL25fill_schema_table_by_openP3THDP11st_mem_rootbP5TABLEP15st_schema_tableP19st_mysql_lex_stringS8_P18Open_tables_backupb + 603
18  mysqld                              0x000000010603a202 _Z14get_all_tablesP3THDP10TABLE_LISTP4Item + 4161
19  mysqld                              0x0000000106040c2a _Z24get_schema_tables_resultP4JOIN23enum_schema_table_state + 721
20  mysqld                              0x000000010602a583 _ZN4JOIN14prepare_resultEv + 129
21  mysqld                              0x0000000105fc1a95 _ZN4JOIN4execEv + 229
22  mysqld                              0x000000010602a0de _Z12handle_queryP3THDP3LEXP12Query_resultyy + 558
23  mysqld                              0x0000000105ffe9cb _ZL21execute_sqlcom_selectP3THDP10TABLE_LIST + 855
24  mysqld                              0x0000000105ff94f7 _Z21mysql_execute_commandP3THDb + 1959
25  mysqld                              0x0000000105ff8361 _Z11mysql_parseP3THDP12Parser_state + 842
26  mysqld                              0x0000000105ff7291 _Z16dispatch_commandP3THDPK8COM_DATA19enum_server_command + 5090
27  mysqld                              0x0000000105ff7e18 _Z10do_commandP3THD + 414
28  mysqld                              0x00000001060b0941 handle_connection + 432
29  mysqld                              0x000000010638013c pfs_spawn_thread + 308
30  libsystem_pthread.dylib             0x00007fff8e60a99d _pthread_body + 131
31  libsystem_pthread.dylib             0x00007fff8e60a91a _pthread_body + 0
32  libsystem_pthread.dylib             0x00007fff8e608351 thread_start + 13

Trying to get some variables.
Some pointers may be invalid and cause the dump to abort.
Query (7fa99912ea30): SELECT * FROM information_schema.REFERENTIAL_CONSTRAINTS
Connection ID (thread ID): 3
Status: NOT_KILLED

The manual page at http://dev.mysql.com/doc/mysql/en/crashing.html contains
information that should help you find out what is causing the crash.


In the interest of time, and because this happened to be an old database whose data could not have changed since the last backup I had, I just reimported its data, and that solved the issue.