SET key_cache_segments leads to crashes in get_partitioned_key_cache_statistics, or safe_mutex_lock, or partitioned_key_cache_statistics

Hi Jean,

Could you please provide your my.cnf file from a server where you observed the crash?

Thanks.

Here is one of the servers conf (the others have similar ones with mainly different buffer_pool_size, key_buffer_size, table_cache and max_connections) :

[client]
port = 3306
socket = /var/run/mysqld/mysqld.sock
[mysqld_safe]
socket = /var/run/mysqld/mysqld.sock
nice = 0
[mysqld]
user = mysql
pid-file = /var/run/mysqld/mysqld.pid
socket = /var/run/mysqld/mysqld.sock
port = 3306
basedir = /usr
datadir = /var/lib/mysql
tmpdir = /tmpfs
skip-external-locking
key_buffer = 512M
max_allowed_packet = 64M
thread_cache_size = 12
myisam-recover = BACKUP
max_connections = 150
table_cache = 16384
table_definition_cache = 16384
query_cache_limit = 1M
query_cache_size = 128M
query_cache_strip_comments = 1
local-infile = 0
open_files_limit = 131072
skip-name-resolve
max_delayed_threads = 1
wait_timeout = 60
interactive_timeout = 60
log_error = /var/log/mysql/error.log
join_buffer_size = 1M
read_buffer_size = 256K
tmp_table_size = 32M
max_heap_table_size = 32M
max_connect_errors = 1000
query_prealloc_size = 131072
query_alloc_block_size = 16384
myisam_sort_buffer_size = 4M
concurrent_insert = 2
read_rnd_buffer_size = 1M
default_storage_engine = InnoDB
innodb_buffer_pool_size = 1280M
innodb_log_file_size = 32M
innodb_flush_log_at_trx_commit = 2
innodb_log_buffer_size = 4M
innodb_file_per_table = 1
innodb_open_files = 400
innodb_file_format = barracuda
key_cache_segments = 8 (wasnt there before i tried to set the value)
log_slow_queries = /var/log/mysql/mysql-slow.log
long_query_time = 2
[mysqldump]
quick
quote-names
max_allowed_packet = 16M
[mysql]
[isamchk]
key_buffer = 16M
!includedir /etc/mysql/conf.d/

And in the conf.d dir :
/etc/mysql/conf.d/mariadb.cnf:[client]
/etc/mysql/conf.d/mariadb.cnf:[mysqld]
/etc/mysql/conf.d/mysqld_safe_syslog.cnf:[mysqld_safe]
/etc/mysql/conf.d/mysqld_safe_syslog.cnf:syslog

Very easy to reproduce. Any myisam workload with 2 or more threads will hit this. Try setting the key_cache_segments to a random value in 1 thread and select/insert/update/show global status/cache index in another thread.

Tttached two examples of a crash.

Jean, Shane, thank you.

Reproducible with the RQG grammar and command line below on maria/5.2 revno 3139, maria/5.3 revno 3539, maria/5.5 revno 3426, and on release versions of 5.2, 5.3, 5.5.

# cat 1.yy
thread1:

  SET GLOBAL key_cache_segments = _digit;

query:
  SHOW GLOBAL STATUS;

# End of RQG grammar

# Run as
perl ./runall.pl \
--grammar=1.yy \
--duration=60 \
--queries=10M \
--threads=2 \
--skip-gendata \
--basedir=<your basedir> \
--vardir=<your vardir>

The other variation of crash can be hit with the following grammar and command line:

# cat 2.yy
query_init:
  SET GLOBAL keycache1.key_buffer_size = 1024*1024;
thread1:
  SET GLOBAL key_cache_segments = _digit;

query:
  CACHE INDEX _table IN keycache1;

# End of RQG grammar

# Run as:

perl ./runall.pl \
--grammar=2.yy \
--duration=60 \
--queries=10M \
--engine=MyISAM \
--threads=2 \
--basedir=<your basedir> \
--vardir=<your vardir>