我在装有 Debian 7.7 的 OpenVZ VPS 上运行 MySQL 5.6.21。MySQL 是从 DotDeb 存储库安装的（完整版本号为 5.6.21-1~dotdeb.1）。
每当 MySQL 服务器启动或重新启动时，它的优先度一开始是 0。然而，大约 20 秒后，它会自动重新调整为 19（最低优先级），我不知道为什么。
我搜索了所有配置文件，确认没有设置 cron 作业来执行此操作，并查看了启动脚本 (/etc/init.d/mysql)。那里没有任何东西会导致此问题。
如果我手动将其重新调整回 0，有时它会保持在 0，有时它最终会再次重新调整为 19。
它不会给托管在此 VPS 上的网站造成任何性能问题（我有一些非常高效的缓存，这限制了甚至接触数据库的需要），但这个小秘密开始让我感到不安。我的职业是 MySQL DBA，并拥有 Oracle 颁发的 MySQL 5.6 数据库管理员认证，但我无法弄清楚这个怪癖……这让我非常沮丧。
当然，我可以设置一个每小时一次的 cron 作业来检查 MySQL 服务器进程的优劣，如果它已发生变化，则将其重新设置为 0，但我想知道为什么会发生这种情况，而不仅仅是对其进行修补。
任何想法或帮助都将不胜感激。谢谢！
/etc/mysql/my.cnf
[client]
socket = /var/run/mysqld/mysqld.sock
[mysqld_safe]
nice = 0
socket = /var/run/mysqld/mysqld.sock
log_error = /var/log/mysql/mysql-error.log
[mysqld]
basedir = /usr
bind_address = 127.0.0.1
connect_timeout = 30
datadir = /var/lib/mysql
innodb_buffer_pool_size = 224M
innodb_file_per_table = 1
innodb_flush_log_at_trx_commit = 2
innodb_log_buffer_size = 4M
innodb_log_file_size = 8M
innodb_open_files = 2048
innodb_thread_concurrency = 8
interactive_timeout = 60
join_buffer_size = 2M
key_buffer_size = 128K
log-queries-not-using-indexes = 1
long_query_time = 2
max_allowed_packet = 16M
max_connections = 125
max_connect_errors = 100
max_heap_table_size = 1M
pid_file = /var/run/mysqld/mysqld.pid
query_cache_limit = 8M
query_cache_min_res_unit = 1K
query_cache_size = 48M
query_cache_type = 1
read_rnd_buffer_size = 1M
skip_external_locking = 1
slow_query_log = 1
slow_query_log_file = /var/log/mysql/mysql-slow.log
socket = /var/run/mysqld/mysqld.sock
sort_buffer_size = 1M
table_definition_cache = 2048
table_open_cache = 2048
table_open_cache_instances = 4
thread_cache_size = 16
tmp_table_size = 1M
user = mysql
wait_timeout = 60
[mysqldump]
max_allowed_packet = 16M
quick
quote_names
[isamchk]
key_buffer = 128K
!includedir /etc/mysql/conf.d/
/etc/mysql/conf.d 中的配置文件内容
#
# The MySQL 5.6 database server configuration file.
#
# This custom MySQL 5.6 specific configuration file
# adds on top of the existing default my.cnf file at
# - /etc/mysql/my.cnf.
#
# Please add any extra MySQL 5.6 options in this file
# for sake of clarity.
#
# You may uncomment any existing option to enable it
#
# sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES
[mysqld_safe]
syslog
/etc/init.d/mysql
#!/bin/bash
#
### BEGIN INIT INFO
# Provides: mysql
# Required-Start: $remote_fs $syslog
# Required-Stop: $remote_fs $syslog
# Should-Start: $network $time
# Should-Stop: $network $time
# Default-Start: 2 3 4 5
# Default-Stop: 0 1 6
# Short-Description: Start and stop the mysql database server daemon
# Description: Controls the main MySQL database server daemon "mysqld"
# and its wrapper script "mysqld_safe".
### END INIT INFO
#
set -e
set -u
${DEBIAN_SCRIPT_DEBUG:+ set -v -x}
test -x /usr/bin/mysqld_safe || exit 0
. /lib/lsb/init-functions
SELF=$(cd $(dirname $0); pwd -P)/$(basename $0)
CONF=/etc/mysql/my.cnf
MYADMIN="/usr/bin/mysqladmin --defaults-file=/etc/mysql/debian.cnf"
# priority can be overriden and "-s" adds output to stderr
ERR_LOGGER="logger -p daemon.err -t /etc/init.d/mysql -i"
# Safeguard (relative paths, core dumps..)
cd /
umask 077
# mysqladmin likes to read /root/.my.cnf. This is usually not what I want
# as many admins e.g. only store a password without a username there and
# so break my scripts.
export HOME=/etc/mysql/
## Fetch a particular option from mysql's invocation.
#
# Usage: void mysqld_get_param option
mysqld_get_param() {
/usr/sbin/mysqld --print-defaults \
| tr " " "\n" \
| grep -- "--$1" \
| tail -n 1 \
| cut -d= -f2
}
## Do some sanity checks before even trying to start mysqld.
sanity_checks() {
# check for config file
if [ ! -r /etc/mysql/my.cnf ]; then
log_warning_msg "$0: WARNING: /etc/mysql/my.cnf cannot be read. See README.Debian.gz"
echo "WARNING: /etc/mysql/my.cnf cannot be read. See README.Debian.gz" | $ERR_LOGGER
fi
# check for diskspace shortage
datadir=`mysqld_get_param datadir`
if LC_ALL=C BLOCKSIZE= df --portability $datadir/. | tail -n 1 | awk '{ exit ($4>4096) }'; then
log_failure_msg "$0: ERROR: The partition with $datadir is too full!"
echo "ERROR: The partition with $datadir is too full!" | $ERR_LOGGER
exit 1
fi
}
## Checks if there is a server running and if so if it is accessible.
#
# check_alive insists on a pingable server
# check_dead also fails if there is a lost mysqld in the process list
#
# Usage: boolean mysqld_status [check_alive|check_dead] [warn|nowarn]
mysqld_status () {
ping_output=`$MYADMIN ping 2>&1`; ping_alive=$(( ! $? ))
ps_alive=0
pidfile=`mysqld_get_param pid-file`
if [ -f "$pidfile" ] && ps `cat $pidfile` >/dev/null 2>&1; then ps_alive=1; fi
if [ "$1" = "check_alive" -a $ping_alive = 1 ] ||
[ "$1" = "check_dead" -a $ping_alive = 0 -a $ps_alive = 0 ]; then
return 0 # EXIT_SUCCESS
else
if [ "$2" = "warn" ]; then
echo -e "$ps_alive processes alive and '$MYADMIN ping' resulted in\n$ping_output\n" | $ERR_LOGGER -p daemon.debug
fi
return 1 # EXIT_FAILURE
fi
}
#
# main()
#
case "${1:-''}" in
'start')
sanity_checks;
# Start daemon
log_daemon_msg "Starting MySQL database server" "mysqld"
if mysqld_status check_alive nowarn; then
log_progress_msg "already running"
log_end_msg 0
else
# Could be removed during boot
test -e /var/run/mysqld || install -m 755 -o mysql -g root -d /var/run/mysqld
# Start MySQL!
su - mysql -s /bin/sh -c "/usr/bin/mysqld_safe > /dev/null 2>&1 &"
# 6s was reported in #352070 to be too few when using ndbcluster
# 14s was reported in #736452 to be too few with large installs
for i in $(seq 1 30); do
sleep 1
if mysqld_status check_alive nowarn ; then break; fi
log_progress_msg "."
done
if mysqld_status check_alive warn; then
log_end_msg 0
# Now start mysqlcheck or whatever the admin wants.
output=$(/etc/mysql/debian-start)
[ -n "$output" ] && log_action_msg "$output"
else
log_end_msg 1
log_failure_msg "Please take a look at the syslog"
fi
fi
;;
'stop')
# * As a passwordless mysqladmin (e.g. via ~/.my.cnf) must be possible
# at least for cron, we can rely on it here, too. (although we have
# to specify it explicit as e.g. sudo environments points to the normal
# users home and not /root)
log_daemon_msg "Stopping MySQL database server" "mysqld"
if ! mysqld_status check_dead nowarn; then
set +e
shutdown_out=`$MYADMIN shutdown 2>&1`; r=$?
set -e
if [ "$r" -ne 0 ]; then
log_end_msg 1
[ "$VERBOSE" != "no" ] && log_failure_msg "Error: $shutdown_out"
log_daemon_msg "Killing MySQL database server by signal" "mysqld"
killall -15 mysqld
server_down=
for i in 1 2 3 4 5 6 7 8 9 10; do
sleep 1
if mysqld_status check_dead nowarn; then server_down=1; break; fi
done
if test -z "$server_down"; then killall -9 mysqld; fi
fi
fi
if ! mysqld_status check_dead warn; then
log_end_msg 1
log_failure_msg "Please stop MySQL manually and read /usr/share/doc/mysql-server-5.6/README.Debian.gz!"
exit -1
else
log_end_msg 0
fi
;;
'restart')
set +e; $SELF stop; set -e
$SELF start
;;
'reload'|'force-reload')
log_daemon_msg "Reloading MySQL database server" "mysqld"
$MYADMIN reload
log_end_msg 0
;;
'status')
if mysqld_status check_alive nowarn; then
log_action_msg "$($MYADMIN version)"
else
log_action_msg "MySQL is stopped."
exit 3
fi
;;
*)
echo "Usage: $SELF start|stop|restart|reload|force-reload|status"
exit 1
;;
esac
答案1
听起来好像它可能被设置在mysqld_safe。曾经有一个关于这个的古老错误。
回想一下mysqld_safe调用mysqld来自无限循环内。
转到操作系统并运行以下命令：
grep -n nice `which mysqld_safe`
这将向您显示所有设置、默认和使用 nice 的地方
我刚刚在运行 MySQL 5.5.20 的 CentOS VM 上运行了这个
[~]# cat /etc/redhat-release
CentOS release 5.7 (Final)
[~]# mysql --version
mysql Ver 14.14 Distrib 5.5.20, for Linux (x86_64) using readline 5.1
[~]# grep -n nice `which mysqld_safe`
17:niceness=0
56: --nice=NICE Set the scheduling priority of mysqld
200: --nice=*) niceness="$val" ;;
629:if test $niceness -eq 0
633: NOHUP_NICENESS="nohup nice -$niceness"
636:# Using nice with no args to get the niceness level is GNU-specific.
638:# BSD could use "nohup sh -c 'ps -o nice -p $$' | tail -1").
641:if nohup nice > /dev/null 2>&1
643: normal_niceness=`nice`
644: nohup_niceness=`nohup nice 2>/dev/null`
646: numeric_nice_values=1
647: for val in $normal_niceness $nohup_niceness
654: numeric_nice_values=0 ;;
658: if test $numeric_nice_values -eq 1
660: nice_value_diff=`expr $nohup_niceness - $normal_niceness`
661: if test $? -eq 0 && test $nice_value_diff -gt 0 && \
662: nice --$nice_value_diff echo testing > /dev/null 2>&1
667: niceness=`expr $niceness - $nice_value_diff`
668: NOHUP_NICENESS="nice -$niceness nohup"
查看第一次出现的 nice（在本例中为 niceness）是否设置为 19。
你也可以直接 grep 查找数字 19mysqld_safe 脚本。
我以前从未听说过随机设置友善度。不过，我首先要说的是，mysqld_safe
请记住，mysqld 可能已作为 nohup 顺利启动。
nice 是 Unix 和类 Unix 操作系统（如 Linux）上的一个程序。它直接映射到同名的内核调用。nice 用于调用具有特定优先级的实用程序或 shell 脚本，从而为该进程提供比其他进程更多或更少的 CPU 时间。nice 值为 -20 表示优先级最高，19 或 20 表示优先级最低。进程的默认 nice 值继承自其父进程，通常为 0。
注意最后一句话
进程的默认优良性是从其父进程继承的，通常为 0。
这听起来令人不安，因为 mysqld 可能会重新继承其原始的 nice 值。谁是mysqld就像我在一开始说的：mysqld_safe。
您还应确保您的操作系统没有以 19 为 nice 运行。只需运行 nice 即可发现。
另外，请注意 nice 的使用信息
[~]# nice --help
Usage: nice [OPTION] [COMMAND [ARG]...]
Run COMMAND with an adjusted niceness, which affects process scheduling.
With no COMMAND, print the current niceness. Nicenesses range from
-20 (most favorable scheduling) to 19 (least favorable).
-n, --adjustment=N add integer N to the niceness (default 10)
--help display this help and exit
--version output version information and exit
NOTE: your shell may have its own version of nice, which usually supersedes
the version described here. Please refer to your shell's documentation
for details about the options it supports.**
Report bugs to <[email protected]>.
根据上述情况NOTE:，你的 shell 的 nice 可能有问题。如果mysqld_safe从上而下继承了它的美好，mysqld将继承了祖父母的善良。