为啥这个查询需要这么长时间？
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【中文标题】为啥这个查询需要这么长时间？【英文标题】：Why does this query take so long?为什么这个查询需要这么长时间？ 【发布时间】：2010-09-13 09:34:02 【问题描述】：我有一个复杂的查询需要在 mysql 服务器上运行。
在我的家庭测试机器上，一个 mac，查询需要 0.00 秒并立即返回结果。
然而，在我的服务器上，一个 ubuntu 机器，相同的查询需要大约 3.30 分钟，使用相同的数据。
数据库使用 InnoDB 表。 ubuntu box有64位内核，mysql就是为此编译的。
为什么 ubuntu 服务器执行查询需要这么长的时间？
这些是来自 ubuntu-box 的配置变量：
mysql> show variables;
+---------------------------------+-----------------------------+
| Variable_name | Value |
+---------------------------------+-----------------------------+
| auto_increment_increment | 1 |
| auto_increment_offset | 1 |
| automatic_sp_privileges | ON |
| back_log | 50 |
| basedir | /usr/ |
| binlog_cache_size | 32768 |
| bulk_insert_buffer_size | 8388608 |
| character_set_client | latin1 |
| character_set_connection | latin1 |
| character_set_database | utf8 |
| character_set_filesystem | binary |
| character_set_results | latin1 |
| character_set_server | latin1 |
| character_set_system | utf8 |
| character_sets_dir | /usr/share/mysql/charsets/ |
| collation_connection | latin1_swedish_ci |
| collation_database | utf8_danish_ci |
| collation_server | latin1_swedish_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 |
| keep_files_on_create | OFF |
| engine_condition_pushdown | OFF |
| expire_logs_days | 10 |
| flush | OFF |
| flush_time | 0 |
| ft_boolean_syntax | + -><()~*:""&| |
| ft_max_word_len | 84 |
| ft_min_word_len | 4 |
| ft_query_expansion_limit | 20 |
| ft_stopword_file | (built-in) |
| group_concat_max_len | 1024 |
| have_archive | YES |
| have_bdb | NO |
| have_blackhole_engine | YES |
| have_compress | YES |
| have_crypt | YES |
| have_csv | YES |
| have_dynamic_loading | YES |
| have_example_engine | NO |
| have_federated_engine | DISABLED |
| have_geometry | YES |
| have_innodb | YES |
| have_isam | NO |
| have_merge_engine | YES |
| have_ndbcluster | DISABLED |
| have_openssl | DISABLED |
| have_ssl | DISABLED |
| have_query_cache | YES |
| have_raid | NO |
| have_rtree_keys | YES |
| have_symlink | YES |
| hostname | databaseserver |
| init_connect | |
| init_file | |
| init_slave | |
| innodb_additional_mem_pool_size | 8388608 |
| innodb_autoextend_increment | 8 |
| innodb_buffer_pool_awe_mem_mb | 0 |
| innodb_buffer_pool_size | 1073741824 |
| innodb_checksums | ON |
| innodb_commit_concurrency | 0 |
| innodb_concurrency_tickets | 500 |
| innodb_data_file_path | ibdata1:10M:autoextend |
| innodb_data_home_dir | |
| innodb_adaptive_hash_index | ON |
| innodb_doublewrite | ON |
| innodb_fast_shutdown | 1 |
| innodb_file_io_threads | 4 |
| innodb_file_per_table | OFF |
| innodb_flush_log_at_trx_commit | 2 |
| innodb_flush_method | O_DIRECT |
| innodb_force_recovery | 0 |
| innodb_lock_wait_timeout | 50 |
| innodb_locks_unsafe_for_binlog | OFF |
| innodb_log_arch_dir | |
| innodb_log_archive | OFF |
| innodb_log_buffer_size | 4194304 |
| 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_support_xa | ON |
| innodb_sync_spin_loops | 20 |
| innodb_table_locks | ON |
| innodb_thread_concurrency | 8 |
| innodb_thread_sleep_delay | 10000 |
| interactive_timeout | 28800 |
| join_buffer_size | 131072 |
| 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 |
| lc_time_names | en_US |
| license | GPL |
| local_infile | ON |
| locked_in_memory | OFF |
| log | OFF |
| log_bin | OFF |
| log_bin_trust_function_creators | OFF |
| log_error | |
| log_queries_not_using_indexes | OFF |
| log_slave_updates | OFF |
| log_slow_queries | ON |
| log_warnings | 1 |
| long_query_time | 1 |
| low_priority_updates | OFF |
| lower_case_file_system | OFF |
| lower_case_table_names | 0 |
| max_allowed_packet | 16777216 |
| max_binlog_cache_size | 18446744073709547520 |
| max_binlog_size | 104857600 |
| max_connect_errors | 10 |
| max_connections | 100 |
| 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 |
| multi_range_count | 256 |
| myisam_data_pointer_size | 6 |
| myisam_max_sort_file_size | 9223372036853727232 |
| myisam_recover_options | BACKUP |
| myisam_repair_threads | 1 |
| myisam_sort_buffer_size | 8388608 |
| myisam_stats_method | nulls_unequal |
| ndb_autoincrement_prefetch_sz | 1 |
| ndb_force_send | ON |
| ndb_use_exact_count | ON |
| ndb_use_transactions | ON |
| ndb_cache_check_time | 0 |
| ndb_connectstring | |
| net_buffer_length | 16384 |
| net_read_timeout | 30 |
| net_retry_count | 10 |
| net_write_timeout | 60 |
| new | OFF |
| old_passwords | OFF |
| open_files_limit | 1024 |
| optimizer_prune_level | 1 |
| optimizer_search_depth | 62 |
| pid_file | /var/run/mysqld/mysqld.pid |
| plugin_dir | |
| port | 3306 |
| preload_buffer_size | 32768 |
| profiling | OFF |
| profiling_history_size | 15 |
| protocol_version | 10 |
| query_alloc_block_size | 8192 |
| query_cache_limit | 1048576 |
| query_cache_min_res_unit | 4096 |
| query_cache_size | 16777216 |
| query_cache_type | ON |
| query_cache_wlock_invalidate | OFF |
| query_prealloc_size | 8192 |
| range_alloc_block_size | 4096 |
| read_buffer_size | 131072 |
| read_only | OFF |
| read_rnd_buffer_size | 262144 |
| relay_log | |
| relay_log_index | |
| relay_log_info_file | relay-log.info |
| relay_log_purge | ON |
| relay_log_space_limit | 0 |
| rpl_recovery_rank | 0 |
| secure_auth | OFF |
| secure_file_priv | |
| server_id | 0 |
| skip_external_locking | ON |
| skip_networking | OFF |
| skip_show_database | OFF |
| slave_compressed_protocol | OFF |
| slave_load_tmpdir | /tmp/ |
| slave_net_timeout | 3600 |
| slave_skip_errors | OFF |
| slave_transaction_retries | 10 |
| slow_launch_time | 2 |
| socket | /var/run/mysqld/mysqld.sock |
| sort_buffer_size | 2097144 |
| sql_big_selects | ON |
| sql_mode | |
| sql_notes | ON |
| 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 | CEST |
| table_cache | 64 |
| table_lock_wait_timeout | 50 |
| table_type | MyISAM |
| thread_cache_size | 8 |
| thread_stack | 131072 |
| time_format | %H:%i:%s |
| time_zone | SYSTEM |
| timed_mutexes | OFF |
| tmp_table_size | 33554432 |
| tmpdir | /tmp |
| transaction_alloc_block_size | 8192 |
| transaction_prealloc_size | 4096 |
| tx_isolation | REPEATABLE-READ |
| updatable_views_with_limit | YES |
| version | 5.0.75-0ubuntu10.5-log |
| version_comment | (Ubuntu) |
| version_compile_machine | x86_64 |
| version_compile_os | debian-linux-gnu |
| wait_timeout | 28800 |
+---------------------------------+-----------------------------+
这是查询：
SELECT work.id work \
, count( DISTINCT( u.id ) ) number_of_editions \
, GROUP_CONCAT( DISTINCT( u.main_title ) ) main_title \
, GROUP_CONCAT( DISTINCT( main_author.full_name ) ) main_author \
, CONCAT_WS(' ', \
GROUP_CONCAT( DISTINCT( u.sub_title_1 ) ) \
,GROUP_CONCAT( DISTINCT( u.sub_title_2 ) ) \
,GROUP_CONCAT( DISTINCT( u.sub_title_3 ) ) \
,GROUP_CONCAT( DISTINCT( u.sub_title_4 ) ) \
,GROUP_CONCAT( DISTINCT( u.sub_title_5 ) ) \
,GROUP_CONCAT( DISTINCT( u.alternative_title ) ) \
,GROUP_CONCAT( DISTINCT( sst.title ) ) \
) boktitler \
, GROUP_CONCAT( DISTINCT( a.full_name ) ) authorname \
, GROUP_CONCAT( DISTINCT( lp.name )) literary_award \
, GROUP_CONCAT( DISTINCT( f.name )) publisher \
, GROUP_CONCAT( DISTINCT( st.title )) series \
, GROUP_CONCAT( DISTINCT( otn.time )) about_period \
, GROUP_CONCAT( DISTINCT( ostn.place )) about_place \
, GROUP_CONCAT( DISTINCT( opn.full_name )) about_person \
, GROUP_CONCAT( DISTINCT( eon.tag )) utag \
, GROUP_CONCAT( DISTINCT( pt.title )) parallell_title \
, work.owners number_of_owners \
FROM core_work work \
LEFT \
JOIN core_edition u \
ON u.work_id = work.id \
LEFT \
JOIN core_author main_author \
ON main_author.edition_id = u.id AND main_author.nr = 1 \
LEFT \
JOIN core_conjoined_title sst \
ON sst.edition_id = u.id \
LEFT \
JOIN core_parallell_title pt \
ON pt.edition_id = u.id \
LEFT \
JOIN core_editiontag eo \
ON eo.edition_id = u.id \
LEFT \
JOIN core_utag eon \
ON eon.id = eo.tag_id \
LEFT \
JOIN core_edition_about_persons op \
ON op.edition_id = u.id \
LEFT \
JOIN core_about_person opn \
ON opn.id = op.about_person_id \
LEFT \
JOIN core_edition_about_place ost \
ON ost.edition_id = u.id \
LEFT \
JOIN core_about_place ostn \
ON ostn.id = ost.about_place_id \
LEFT \
JOIN core_edition_abouttime ot \
ON ot.edition_id = u.id \
LEFT \
JOIN core_abouttime otn \
ON otn.id = ot.abouttime_id \
LEFT \
JOIN core_seriesnr vs \
ON vs.edition_id = u.id \
LEFT \
JOIN core_series st \
ON st.id = vs.series_id \
LEFT \
JOIN core_edition_publisher uf \
ON uf.edition_id = u.id \
LEFT \
JOIN core_publisher f \
ON f.id = uf.publisher_id \
LEFT \
JOIN core_author a \
ON a.edition_id = u.id AND a.nr > 1 \
LEFT \
JOIN core_awarded_literary_award tlp \
ON tlp.edition_id = u.id \
LEFT \
JOIN core_literary_award lp \
ON tlp.literary_award_id = lp.id \
LEFT \
JOIN core_source source \
ON u.source_id = source.id \
WHERE u.hidden = 0 \
AND number_of_editions > 0 \
GROUP \
BY work.id \
LIMIT 1;
两个数据库中的数据应该是相同的（我从一个转储到文件并恢复到另一个）。当我执行 EXPLAIN SELECT 时，答案之间存在差异：（删除了相同的行）
快速测试机：
+----+-------------+-------------+--------+---------------------------------------+---------------------------------------+---------+-----------------------------------+------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------------+--------+---------------------------------------+---------------------------------------+---------+-----------------------------------+------+-------------+
| 1 | SIMPLE | work | index | PRIMARY,work_number_of_editions | PRIMARY | 4 | NULL | 2 | Using where |
+----+-------------+-------------+--------+---------------------------------------+---------------------------------------+---------+-----------------------------------+------+-------------+
慢机器：
+----+-------------+-------------+--------+---------------------------------------+---------------------------------------+---------+-----------------------------------+--------+-----------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------------+--------+---------------------------------------+---------------------------------------+---------+-----------------------------------+--------+-----------------------------+
| 1 | SIMPLE | work | range | PRIMARY,work_number_of_editions | work_number_of_editions | 5 | NULL | 106796 | Using where; Using filesort |
+----+-------------+-------------+--------+---------------------------------------+---------------------------------------+---------+-----------------------------------+--------+-----------------------------+
这让我很困惑；为什么 ubuntu 服务器与另一个服务器具有相同的数据时会报告 106796 行？以及为什么慢机器使用文件排序？
【问题讨论】：
您是否比较了两个系统上的计划？ 为了更好地比较两台服务器，请添加 SQL_NO_CACHE 选项。 @Dennis Haarbrink：SQL_NO_CACHE 在这里什么都不做。它是查询缓存的控件。 @Morgan Tocker：我知道，但是当查询结果被缓存时，你会得到一个错误的比较。 【参考方案1】：尝试在两台服务器上使用EXPLAIN SELECT ...。这将显示正在使用哪些索引以及如何使用。如果两台机器上的设置有任何差异，它应该会影响查询计划（例如，某些表在您的服务器上缺少索引）。
两台机器上的数据集是否相同？如果您的家用计算机上只有一小部分数据，而服务器上有完整的“较大”数据集，那也会影响事情。您正在使用 lot 的 DISTINCT 修饰符和 GROUP_CONCATS 并加入大量表。这可能需要使用大量临时表，并且您可能会超出可用内存，从而迫使 MySQL 使用磁盘缓冲，这与内存中的操作相比非常慢。
【讨论】：
现在我已经从 ubuntu 盒子中转储了所有表并导入到测试机器中。它们现在应该是相同的。但是，EXPLAIN SELECT 不一样：我将编辑我的问题以包含不同的响应。 你在 home box 上运行什么版本的 MySQL？从 ubuntu 服务器版本的外观来看，它来自旧版本，因为 Ubuntu 10.04LTS 附带 v5.1.41。 在我的测试机器上，我在 mac 上从 macports 运行 MySQL 5.5.2-m2。 这是一个相当大的区别。 5.5 是具有大量内部更改的开发/前沿版本，这可以解释查询性能的差异。我建议降级到更接近你的 ubuntu 机器上的版本，看看这是否会让你的 Mac 和服务器一样慢。【参考方案2】：尝试OPTIMIZE和ANALYZE所有表格
【讨论】：
现在我都做了，一切都OK了。不幸的是，它并没有提高性能。以上是关于为啥这个查询需要这么长时间？的主要内容，如果未能解决你的问题，请参考以下文章
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