我们有一台带有4GB RAM和MySQL 5.1.41的Linux服务器。我们在MySQL上有默认设置。 我们运行实时社交网络服务，类似于Twitter。 数据库由1,4 miljon推文条目组成。 我们的Web和桌面客户端每隔5秒获取一次发送查询的新条目。我们现在正在测试几乎没有客户端的系统，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，我们期望有几百个客户端，这可能会挂起实例。 来自Mysql性能专家的任何建议？
`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
character_set_connection utf8
character_set_database utf8
character_set_filesystem binary
character_set_results utf8
character_set_server utf8
character_set_system utf8
character_sets_dir /usr/share/mysql/charsets/
collation_connection utf8_general_ci
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
error_count 0
event_scheduler OFF
example_enum_var e1
example_ulong_var 8
expire_logs_days 10
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
innodb_autoextend_increment 8
innodb_autoinc_lock_mode 1
innodb_buffer_pool_size 8388608
innodb_checksums ON
innodb_commit_concurrency 0
innodb_concurrency_tickets 500
innodb_data_file_path ibdata1:10M:autoextend
innodb_data_home_dir
innodb_doublewrite ON
innodb_fast_shutdown 1
innodb_file_io_threads 4
innodb_file_per_table OFF
innodb_flush_log_at_trx_commit 1
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 ./
innodb_max_dirty_pages_pct 90
innodb_max_purge_lag 0
innodb_mirrored_log_groups 1
innodb_open_files 300
innodb_rollback_on_timeout OFF
innodb_stats_on_metadata ON
innodb_support_xa ON
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
ndb_index_stat_cache_entries 32
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
old_alter_table OFF
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
skip_external_locking ON
skip_networking OFF
skip_show_database OFF
slave_allow_batching OFF
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
sql_safe_updates OFF
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
答案 0 :(得分：2)
你应该在channel_id，userid，type，public和time_added上有索引。
答案 1 :(得分：0)
我们在MySQL上有默认设置
这不好，因为那些是相当保守的价值观。如果你的存储引擎是InnoDB（如果没有，那么切换到它），那么默认的缓存大小是8MB - 所以你的另外4GB的RAM是没用的。
将innodb_buffer_pool_size设置为3GB（如果这是一个数据库专用服务器） - 否则在那里放一些不错的值。
另外，请告诉我们该表上的索引。
答案 2 :(得分：0)
在询问有关MySQL查询性能的问题时，您应始终发布以下内容：
SHOW CREATE TABLE tablename
EXPLAIN SELECT query_goes_here
SHOW VARIABLES
正在发生的事情是您的表可能没有按照预期进行优化，因为MySQL在默认设置下运行 - 它针对慢速计算机进行了调整，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索引你所加入的所有内容 - 在所有情况下都不是这样，基数在选择索引时起作用。 / p>
您应该编辑您的问题并向我们提供更多数据。