MySQL 查询的性能问题优化最佳实践？

Question

我们有一台具有 4GB RAM 和 MySQL 5.1.41 的 Linux 服务器。我们对 MySQL 有默认设置。 我们运行实时社交网络服务，类似于 Twitter。 数据库由 140 万条推文条目组成。 我们的网络和桌面客户端每 5 秒获取一次发送查询的新条目。我们现在正在用很少的客户端测试系统，但它挂起了 SQL - 每个请求都有效 15 秒。 如果删除“order by” - 时间减少一半但仍然太慢，我们预计会有数百个客户端，这可能会挂起实例。 Mysql 性能专家有什么建议吗？

`SELECT
                                   A.ID id,
                                   A.msg,
                                   A.pic,
                                   A.time_added,
                                   A.public,
                                   A.twitter_status_id,
                                   A.twitter_update_type,
                                   A.USERID userid,
                                  A.pic_host,
                                   B.ppic_host,
                                   B.username,
                                   B.profilepicture
                                   FROM posts A, members B WHERE

(A.channel_id IN (489, 109, 490, 4, 493, 494, 495, 496, 497, 452, 80, 53, 198, 834, 498, 500, 501, 852, 505, 506, 507, 508, 509, 510, 511, 778, 515, 132, 517, 519, 931, 932, 934, 521, 523, 524, 780, 569, 527, 12, 529, 530, 532, 533, 534, 936, 938, 536, 537, 708, 940, 704)

AND A.USERID=B.USERID
AND A.type='update'
AND A.public=1
AND A.TIME_ADDED>1305543735)

order by A.TIME_ADDED
desc limit 50;


 mysql> EXPLAIN
    ->
    -> SELECT
    ->                                    A.ID id,
    ->                                    A.msg,
    ->                                    A.pic,
    ->                                    A.time_added,
    ->                                    A.public,
    ->                                    A.twitter_status_id,
    ->                                    A.twitter_update_type,
    ->                                    A.USERID userid,
    ->                                   A.pic_host,
    ->                                    B.ppic_host,
    ->                                    B.username,
    ->                                    B.profilepicture
    ->                                    FROM posts A, members B WHERE
    ->
    -> (A.channel_id IN (489, 109, 490, 4, 493, 494, 495, 496, 497, 452, 80, 53, 198, 834, 498, 500, 501, 852, 505, 506, 507, 508, 509, 510, 511, 778, 515, 132, 517, 519, 931, 932, 934, 521, 523, 524, 780, 569, 527, 12, 529, 530, 532, 533, 534, 936, 938, 536, 537, 708, 940, 704)
    ->
    -> AND A.USERID=B.USERID
    -> AND A.type='update'
    -> AND A.public=1
    -> AND A.TIME_ADDED>1305543735)
    ->
    -> order by A.TIME_ADDED
    -> desc limit 50;
+----+-------------+-------+--------+-----------------------------------------------+------------+---------+------------------------+------+-------------+
| id | select_type | table | type   | possible_keys                                 | key        | key_len | ref                    | rows | Extra       |
+----+-------------+-------+--------+-----------------------------------------------+------------+---------+------------------------+------+-------------+
|  1 | SIMPLE      | A     | range  | USERID,type,time_added,userid+type,channel_id | time_added | 5       | NULL                   |   18 | Using where |
|  1 | SIMPLE      | B     | eq_ref | PRIMARY,USERID                                | PRIMARY    | 8       | twitter_devel.A.USERID |    1 |             |
+----+-------------+-------+--------+-----------------------------------------------+------------+---------+------------------------+------+-------------+
2 rows in set (0.00 sec)


   DDL for table posts:

CREATE TABLE `posts` (
  `ID` bigint(20) NOT NULL AUTO_INCREMENT,
  `type` varchar(10) NOT NULL,
  `USERID` bigint(20) NOT NULL,
  `PID` bigint(20) NOT NULL,
  `UID` bigint(20) NOT NULL,
  `UIDO` bigint(20) NOT NULL,
  `channel_id` bigint(20) DEFAULT NULL,
  `msg` text NOT NULL,
  `pic` varchar(20) NOT NULL,
  `pic_host` varchar(40) DEFAULT NULL,
  `pdf_host` varchar(40) DEFAULT NULL,
  `time_added` int(10) DEFAULT NULL,
  `views` bigint(20) NOT NULL,
  `reply` bigint(20) NOT NULL,
  `edited` varchar(20) NOT NULL,
  `public` int(11) NOT NULL DEFAULT '1',
  `twitter_status_id` bigint(50) DEFAULT NULL,
  `twitter_update_type` varchar(10) DEFAULT NULL,
  PRIMARY KEY (`ID`),
  UNIQUE KEY `ID` (`ID`),
  KEY `USERID` (`USERID`),
  KEY `type` (`type`),
  KEY `UID` (`UID`),
  KEY `time_added` (`time_added`),
  KEY `userid+type` (`type`,`USERID`) USING BTREE,
  KEY `pic` (`pic`),
  KEY `channel_id` (`channel_id`),
  FULLTEXT KEY `msg` (`msg`)
) ENGINE=MyISAM AUTO_INCREMENT=1591683 DEFAULT CHARSET=utf8;

    auto_increment_increment    2
auto_increment_offset   2
autocommit  ON
automatic_sp_privileges ON
back_log    50
basedir /usr/
big_tables  OFF
binlog_cache_size   32768
binlog_format   MIXED
bulk_insert_buffer_size 8388608
character_set_client    utf8
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character_set_results   utf8
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character_set_system    utf8
character_sets_dir  /usr/share/mysql/charsets/
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collation_database  utf8_general_ci
collation_server    utf8_unicode_ci
completion_type 0
concurrent_insert   1
connect_timeout 10
datadir /var/lib/mysql/
date_format %Y-%m-%d
datetime_format %Y-%m-%d %H:%i:%s
default_week_format 0
delay_key_write ON
delayed_insert_limit    100
delayed_insert_timeout  300
delayed_queue_size  1000
div_precision_increment 4
engine_condition_pushdown   ON
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event_scheduler OFF
example_enum_var    e1
example_ulong_var   8
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flush   OFF
flush_time  0
foreign_key_checks  ON
ft_boolean_syntax   + -><()~*:""&|
ft_max_word_len 84
ft_min_word_len 4
ft_query_expansion_limit    20
ft_stopword_file    (built-in)
general_log OFF
general_log_file    /var/run/mysql/mysqld.log
group_concat_max_len    1024
have_community_features YES
have_compress   YES
have_crypt  YES
have_csv    YES
have_dynamic_loading    YES
have_geometry   YES
have_innodb YES
have_ndbcluster DISABLED
have_openssl    DISABLED
have_partitioning   YES
have_query_cache    YES
have_rtree_keys YES
have_ssl    DISABLED
have_symlink    YES
hostname    vteu02.veritweet.com
identity    0
ignore_builtin_innodb   OFF
init_connect    
init_file   
init_slave  
innodb_adaptive_hash_index  ON
innodb_additional_mem_pool_size 1048576
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innodb_data_home_dir    
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innodb_flush_method 
innodb_force_recovery   0
innodb_lock_wait_timeout    50
innodb_locks_unsafe_for_binlog  OFF
innodb_log_buffer_size  1048576
innodb_log_file_size    5242880
innodb_log_files_in_group   2
innodb_log_group_home_dir   ./
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innodb_sync_spin_loops  20
innodb_table_locks  ON
innodb_thread_concurrency   8
innodb_thread_sleep_delay   10000
innodb_use_legacy_cardinality_algorithm ON
insert_id   0
interactive_timeout 28800
join_buffer_size    131072
keep_files_on_create    OFF
key_buffer_size 16777216
key_cache_age_threshold 300
key_cache_block_size    1024
key_cache_division_limit    100
language    /usr/share/mysql/english/
large_files_support ON
large_page_size 0
large_pages OFF
last_insert_id  0
lc_time_names   en_US
license GPL
local_infile    ON
locked_in_memory    OFF
log OFF
log_bin ON
log_bin_trust_function_creators OFF
log_bin_trust_routine_creators  OFF
log_error   /var/log/mysql/mysqld.log
log_output  FILE
log_queries_not_using_indexes   ON
log_slave_updates   OFF
log_slow_queries    ON
log_warnings    1
long_query_time 10.000000
low_priority_updates    OFF
lower_case_file_system  OFF
lower_case_table_names  0
max_allowed_packet  1048576
max_binlog_cache_size   18446744073709547520
max_binlog_size 524288000
max_connect_errors  10
max_connections 151
max_delayed_threads 20
max_error_count 64
max_heap_table_size 16777216
max_insert_delayed_threads  20
max_join_size   18446744073709551615
max_length_for_sort_data    1024
max_prepared_stmt_count 16382
max_relay_log_size  0
max_seeks_for_key   18446744073709551615
max_sort_length 1024
max_sp_recursion_depth  0
max_tmp_tables  32
max_user_connections    0
max_write_lock_count    18446744073709551615
min_examined_row_limit  0
multi_range_count   256
myisam_data_pointer_size    6
myisam_max_sort_file_size   9223372036853727232
myisam_recover_options  OFF
myisam_repair_threads   1
myisam_sort_buffer_size 8388608
myisam_stats_method nulls_unequal
myisam_use_mmap OFF
ndb_autoincrement_prefetch_sz   1
ndb_batch_size  32768
ndb_cache_check_time    0
ndb_connectstring   
ndb_extra_logging   1
ndb_force_send  ON
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ndb_index_stat_enable   OFF
ndb_index_stat_update_freq  20
ndb_log_binlog_index    ON
ndb_log_update_as_write ON
ndb_log_updated_only    ON
ndb_optimization_delay  10
ndb_optimized_node_selection    3
ndb_report_thresh_binlog_epoch_slip 3
ndb_report_thresh_binlog_mem_usage  10
ndb_table_no_logging    OFF
ndb_table_temporary OFF
ndb_use_copying_alter_table OFF
ndb_use_exact_count OFF
ndb_use_transactions    ON
ndbinfo_database    ndbinfo
ndbinfo_max_bytes   0
ndbinfo_max_rows    10
ndbinfo_show_hidden OFF
ndbinfo_table_prefix    ndb$
ndbinfo_version 458765
net_buffer_length   8192
net_read_timeout    30
net_retry_count 10
net_write_timeout   60
new OFF
old OFF
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old_passwords   OFF
open_files_limit    1024
optimizer_prune_level   1
optimizer_search_depth  62
optimizer_switch    index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on
pid_file    /var/run/mysql/mysqld.pid
plugin_dir  /usr/lib64/mysql/plugin
port    3306
preload_buffer_size 32768
profiling   ON
profiling_history_size  15
protocol_version    10
pseudo_thread_id    304885
query_alloc_block_size  8192
query_cache_limit   1048576
query_cache_min_res_unit    4096
query_cache_size    0
query_cache_type    ON
query_cache_wlock_invalidate    OFF
query_prealloc_size 8192
rand_seed1  
rand_seed2  
range_alloc_block_size  4096
read_buffer_size    262144
read_only   OFF
read_rnd_buffer_size    524288
relay_log   /var/lib/mysql/slave-relay.log
relay_log_index /var/lib/mysql/slave-relay-log.index
relay_log_info_file relay-log.info
relay_log_purge ON
relay_log_space_limit   0
report_host 
report_password 
report_port 3306
report_user 
rpl_recovery_rank   0
secure_auth OFF
secure_file_priv    
server_id   22
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skip_networking OFF
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slave_compressed_protocol   OFF
slave_exec_mode STRICT
slave_load_tmpdir   /var/tmp/mysql.XeaVJ2
slave_net_timeout   3600
slave_skip_errors   OFF
slave_transaction_retries   10
slow_launch_time    2
slow_query_log  ON
slow_query_log_file /var/run/mysql/mysqld-slow.log
socket  /var/run/mysql/mysql.sock
sort_buffer_size    524288
sql_auto_is_null    ON
sql_big_selects ON
sql_big_tables  OFF
sql_buffer_result   OFF
sql_log_bin ON
sql_log_off OFF
sql_log_update  ON
sql_low_priority_updates    OFF
sql_max_join_size   18446744073709551615
sql_mode    
sql_notes   ON
sql_quote_show_create   ON
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sql_select_limit    18446744073709551615
sql_slave_skip_counter  
sql_warnings    OFF
ssl_ca  
ssl_capath  
ssl_cert    
ssl_cipher  
ssl_key 
storage_engine  MyISAM
sync_binlog 0
sync_frm    ON
system_time_zone    EEST
table_definition_cache  256
table_lock_wait_timeout 50
table_open_cache    64
table_type  MyISAM
thread_cache_size   0
thread_handling one-thread-per-connection
thread_stack    262144
time_format %H:%i:%s
time_zone   SYSTEM
timed_mutexes   OFF
timestamp   1305623046
tmp_table_size  16777216
tmpdir  /var/tmp/mysql.XeaVJ2
transaction_alloc_block_size    8192
transaction_allow_batching  ON
transaction_prealloc_size   4096
tx_isolation    REPEATABLE-READ
unique_checks   ON
updatable_views_with_limit  YES
version 5.1.41-ndb-7.0.13-log
version_comment SUSE MySQL Cluster RPM
version_compile_machine x86_64
version_compile_os  suse-linux-gnu
wait_timeout    28800
warning_count   0

Answer 1

您应该在channel_id、userid、type、public 和time_added 上有索引。

Answer 2

我们对 MySQL 有默认设置

这不好，因为这些都是相当保守的值。如果您的存储引擎是 InnoDB（如果不是，则切换到它），那么默认缓存大小为 8MB - 所以您的其他 4GB RAM 几乎没有用处。

将 innodb_buffer_pool_size 设置为 3GB（如果这是一个数据库专用服务器） - 否则在那里放置一些不错的值。

另外，请告诉我们该表上的索引。

Answer 3

当询问有关 MySQL 查询性能的问题时，您应该始终发布以下内容：

SHOW CREATE TABLE tablename 的输出

EXPLAIN SELECT query_goes_here

的输出 SHOW VARIABLES< /code>

发生的情况是，您的表可能没有按照应有的方式进行优化，并且由于 MySQL 在默认设置上运行 - 它针对慢速机器进行了调整，并且没有使用您可能拥有的任何高级硬件支持。

现在，在选择索引时 - 必须考虑几个因素，我读过有人提到你应该对你加入的所有内容建立索引 - 这并非在所有情况下都是正确的，基数在选择索引时发挥着作用。

您应该编辑您的问题并向我们提供更多数据。