linux下 mysql 300万数据查询500多秒怎么优化啊，其中pid已经做索引,id是主键
SELECT id,pid,keyWords,shortUrl FROM keywords WHERE pid=0 ORDER BY id DESC LIMIT 50
explain 如下：
mysql> explain SELECT id,pid,keyWords,shortUrl FROM keywords WHERE pid=0 ORDER BY id DESC LIMIT 50;
+----+-------------+----------+------+---------------+------+---------+-------+---------+-----------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+----------+------+---------------+------+---------+-------+---------+-----------------------------+
| 1 | SIMPLE | keywords | ref | pid | pid | 4 | const | 2452523 | Using where; Using filesort |
+----+-------------+----------+------+---------------+------+---------+-------+---------+-----------------------------+
1 row in set (8.18 sec)
另外mysql cpu占用很高怎么回事？内存:512M
配置文件如下：
# Example MySQL config file for small systems.
#
# This is for a system with little memory (<= 64M) where MySQL is only used
# from time to time and it's important that the mysqld daemon
# doesn't use much resources.
#
# You can copy this file to
# /etc/my.cnf to set global options,
# mysql-data-dir/my.cnf to set server-specific options (in this
# installation this directory is /usr/local/mysql/var) or
# ~/.my.cnf to set user-specific options.
#
# In this file, you can use all long options that a program supports.
# If you want to know which options a program supports, run the program
# with the "--help" option.
# The following options will be passed to all MySQL clients
[client]
#password = your_password
port = 3306
socket = /tmp/mysql.sock
# Here follows entries for some specific programs
# The MySQL server
[mysqld]
port = 3306
socket = /tmp/mysql.sock
skip-locking
key_buffer = 16K
max_allowed_packet = 1M
table_cache = 4
sort_buffer_size = 64K
read_buffer_size = 256K
read_rnd_buffer_size = 256K
net_buffer_length = 2K
thread_stack = 64K
datadir=/www/mysql/data
log-slow-queries=/www/log/mysql/slowquery.log
long_query_time=2
# Don't listen on a TCP/IP port at all. This can be a security enhancement,
# if all processes that need to connect to mysqld run on the same host.
# All interaction with mysqld must be made via Unix sockets or named pipes.
# Note that using this option without enabling named pipes on Windows
# (using the "enable-named-pipe" option) will render mysqld useless!
#
#skip-networking
server-id = 1
# Uncomment the following if you want to log updates
#log-bin=mysql-bin
# Uncomment the following if you are NOT using BDB tables
#skip-bdb
# Uncomment the following if you are using InnoDB tables
#innodb_data_home_dir = /usr/local/mysql/var/
#innodb_data_file_path = ibdata1:10M:autoextend
#innodb_log_group_home_dir = /usr/local/mysql/var/
#innodb_log_arch_dir = /usr/local/mysql/var/
# You can set .._buffer_pool_size up to 50 - 80 %
# of RAM but beware of setting memory usage too high
#innodb_buffer_pool_size = 16M
#innodb_additional_mem_pool_size = 2M
# Set .._log_file_size to 25 % of buffer pool size
#innodb_log_file_size = 5M
#innodb_log_buffer_size = 8M
#innodb_flush_log_at_trx_commit = 1
#innodb_lock_wait_timeout = 50
[mysqldump]
quick
max_allowed_packet = 16M
[mysql]
no-auto-rehash