作/译者：叶金荣（Email: ），来源：http://imysql.cn，转载请注明作/译者和出处，并且不能用于商业用途，违者必究。

环境说明

OS: AS4U6, 2.6.9-67.0.15.ELsmp, 16G Ram, MD3000阵列, xfs文件系统
MySQL 5.1.26 - percona(innodb plugin, innodb stat, user stat, msl, show patch, acc-pslist 补丁)

default_table_type = innodb
log_slow_queries
long_query_time = 0.001
log_slow_verbosity=query_plan,innodb
innodb_data_file_path = ibdata1:1024M:autoextend
innodb_log_file_size = 400M
innodb_log_files_in_group = 3
innodb_file_per_table
innodb_file_format="Barracuda"

innodb_buffer_pool_size = 8388608
join_buffer_size = 131072
key_buffer_size = 8388600
max_heap_table_size = 16777216
query_cache_size = 0
read_buffer_size = 131072
read_rnd_buffer_size = 262144
sort_buffer_size = 2097144
tmp_table_size = 16777216

1、 排序缓冲

1.1 利用InnoDB的主键进行排序

EXPLAIN SELECT SQL_NO_CACHE * FROM T1 WHERE ID<10000 ORDER BY ID DESC;
+----+-------------+-------+-------+---------------+---------+---------+------+-------+-------------+
| id | select_type | table | type  | possible_keys | key     | key_len | ref  | rows  | Extra       |
+----+-------------+-------+-------+---------------+---------+---------+------+-------+-------------+
|  1 | SIMPLE      | T1    | range | PRIMARY       | PRIMARY | 8       | NULL | 14872 | Using where |
+----+-------------+-------+-------+---------------+---------+---------+------+-------+-------------+
# Query_time: 0.207893  Lock_time: 0.000056  Rows_sent: 9999  Rows_examined: 9999
# QC_Hit: No  Full_scan: No  Full_join: No  Tmp_table: No  Tmp_table_on_disk: No
# Filesort: No  Filesort_on_disk: No  Merge_passes: 0
#   InnoDB_IO_r_ops: 91  InnoDB_IO_r_bytes: 1490944  InnoDB_IO_r_wait: 0.083391
#   InnoDB_rec_lock_wait: 0.000000  InnoDB_queue_wait: 0.000000
#   InnoDB_pages_distinct: 93
SELECT SQL_NO_CACHE * FROM T1 WHERE ID<10000 ORDER BY ID DESC;

1.2 利用 InnoDB 使用非索引字段排序

EXPLAIN SELECT SQL_NO_CACHE * FROM T1 WHERE ID<10000 ORDER BY C1 DESC;
+----+-------------+-------+-------+---------------+---------+---------+------+-------+-----------------------------+
| id | select_type | table | type  | possible_keys | key     | key_len | ref  | rows  | Extra                       |
+----+-------------+-------+-------+---------------+---------+---------+------+-------+-----------------------------+
|  1 | SIMPLE      | T1    | range | PRIMARY       | PRIMARY | 8       | NULL | 14872 | Using where; Using filesort |
+----+-------------+-------+-------+---------------+---------+---------+------+-------+-----------------------------+
# Query_time: 0.120879  Lock_time: 0.000023  Rows_sent: 9999  Rows_examined: 19998
# QC_Hit: No  Full_scan: No  Full_join: No  Tmp_table: No  Tmp_table_on_disk: No
# Filesort: Yes  Filesort_on_disk: Yes  Merge_passes: 1
#   InnoDB_IO_r_ops: 0  InnoDB_IO_r_bytes: 0  InnoDB_IO_r_wait: 0.000000
#   InnoDB_rec_lock_wait: 0.000000  InnoDB_queue_wait: 0.000000
#   InnoDB_pages_distinct: 93
SELECT SQL_NO_CACHE * FROM T1 WHERE ID<10000 ORDER BY C1 DESC;

set session sort_buffer_size = 1024 * 1024 * 5;

# Query_time: 0.080727  Lock_time: 0.000030  Rows_sent: 9999  Rows_examined: 19998
# QC_Hit: No  Full_scan: No  Full_join: No  Tmp_table: No  Tmp_table_on_disk: No
# Filesort: Yes  Filesort_on_disk: No  Merge_passes: 0
#   InnoDB_IO_r_ops: 0  InnoDB_IO_r_bytes: 0  InnoDB_IO_r_wait: 0.000000
#   InnoDB_rec_lock_wait: 0.000000  InnoDB_queue_wait: 0.000000
#   InnoDB_pages_distinct: 93
SELECT SQL_NO_CACHE * FROM T1 WHERE ID<10000 ORDER BY C1 DESC;

1.3 加大 read_rnd_buffer_size 看看对 filesort 是否有影响

EXPLAIN SELECT SQL_NO_CACHE * FROM T1 AS T1 WHERE ID<10000 ORDER BY C1 DESC;
+----+-------------+-------+-------+---------------+---------+---------+------+-------+-----------------------------+
| id | select_type | table | type  | possible_keys | key     | key_len | ref  | rows  | Extra                       |
+----+-------------+-------+-------+---------------+---------+---------+------+-------+-----------------------------+
|  1 | SIMPLE      | T1    | range | PRIMARY       | PRIMARY | 8       | NULL | 14872 | Using where; Using filesort |
+----+-------------+-------+-------+---------------+---------+---------+------+-------+-----------------------------+
# Query_time: 0.103654  Lock_time: 0.000045  Rows_sent: 9999  Rows_examined: 19998
# QC_Hit: No  Full_scan: No  Full_join: No  Tmp_table: No  Tmp_table_on_disk: No
# Filesort: Yes  Filesort_on_disk: Yes  Merge_passes: 1
#   InnoDB_IO_r_ops: 0  InnoDB_IO_r_bytes: 0  InnoDB_IO_r_wait: 0.000000
#   InnoDB_rec_lock_wait: 0.000000  InnoDB_queue_wait: 0.000000
#   InnoDB_pages_distinct: 93
SELECT SQL_NO_CACHE * FROM T1 AS T1 WHERE ID<10000 ORDER BY C1 DESC;