查看mysql查询缓存内容
View mysql query cache contents
我有一个使用 mysqls 查询缓存功能的大型数据库应用程序。我想检查查询缓存的内容以识别不应缓存的条目（例如，通过使用 SELECT SQL_NO_CACHE...），因为我想优化我的应用程序。
有没有办法从查询缓存中获取缓存条目的列表？
-- 编辑：Rick 建议的附加信息 ---
1) RAM 大小为 16GB
2) 显示变量；
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version 5.1.56-log
version_comment Gentoo Linux mysql-5.1.56
version_compile_machine x86_64
version_compile_os pc-linux-gnu
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3) 显示全局状态；
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您可以知道使用
缓存的查询数量
Show status like 'Qcache_queries_in_cache'
它将在 value 列中为您提供缓存查询的数量。
只有查询的散列存储在 Qcache 中。
无法找到实际缓存了哪些查询。
了解它的一种可能方法是执行您的查询之一并检查 value 列的更改。
如果你有一个 "large" 数据库应用程序，这意味着有很多写入？请记住，当 any 写入 table 时，table 的 all QC 条目将被清除。这意味着您可能无法从 QC 中受益。
此外，清除需要付出努力，从而减慢系统速度。对于query_cache_size下，比如50M，开销不大。但是如果你有1G的QC，你刷QC的时间会比使用QC的时间还长！
无法发现QC 中的实际查询。以下是 可能 的帮助：将 SQL_NO_CACHE 放在任何涉及经常更改的 table(s) 的查询上。将 SQL_CACHE 放在其余部分。然后使用DEMAND。监控 STATUS LIKE Qc%.
如果您想分析您的系统（QC 或其他），请提供 (1) RAM 大小，(2) 显示变量，(3) 在服务器启动至少一天后显示全局状态.
观察：
版本：5.1.56-log
16 GB 内存
正常运行时间 = 53d 21:20:56
您不在 Windows 上 运行。
运行 64 位版本
看来您是 运行 MyISAM 和 InnoDB。
更重要的问题
key_buffer_size = 1500M
innodb_buffer_pool_size = 2000M
join_buffer_size = 1M -- This may be the most important
tmp_table_size = 256M -- Also important
query_cache_size = 50M -- as already mentioned
Use slowlog to find tmp tables spilling to disk
三个设置特别高，可能导致 paging/swapping。 MySQL 性能在 paged/swapped 时受到严重影响。与其发生这种情况，不如降低设置。
细节和小问题
( innodb_buffer_pool_size / _ram ) = 1024M / 16384M = 6.2% -- 用于 InnoDB 的 RAM 百分比 buffer_pool
( Innodb_pages_written / Innodb_buffer_pool_write_requests ) = 29,673,396 / 196667000 = 15.1% -- 必须写入磁盘的写入请求
-- 检查 innodb_buffer_pool_size
( Innodb_buffer_pool_read_ahead_evicted / Innodb_buffer_pool_read_ahead ) = 4,691,916 / 30144135 = 15.6% -- read_ahead 的效用。
-- 关闭预读
( Innodb_os_log_written / (Uptime / 3600) / innodb_log_files_in_group / innodb_log_file_size ) = 34,746,359,296 / (4656056 / 3600) / 2 / 256M = 0.05 -- 比率
( Uptime / 60 * innodb_log_file_size / Innodb_os_log_written ) = 4,656,056 / 60 * 256M / 34746359296 = 599 -- InnoDB 日志轮换之间的分钟数 从 5.6.8 开始，可以动态更改;请务必也更改 my.cnf。
--（轮换间隔 60 分钟的建议有些武断。）
( table_open_cache ) = 4,096 -- 要缓存的 table 个描述符的数量
-- 一般几百就可以了。
( innodb_stats_on_metadata ) = ON -- 触摸统计数据时重新分析 table。
-- ON 可能会减慢某些 SHOW 和 information_schema 访问。
( join_buffer_size ) = 2,147,483,648 = 2048MB -- 每个线程 0-N。可能会加速 JOIN（最好修复 queries/indexes）（所有引擎）用于索引扫描、范围索引扫描、全 table 扫描、每个全 JOIN 等。
-- 使用默认值。
( join_buffer_size / _ram ) = 2,147,483,648 / 16384M = 12.5% -- 每个线程 0-N。可能会加速 JOIN（最好修复 queries/indexes）（所有引擎）用于索引扫描、范围索引扫描、全 table 扫描、每个全 JOIN 等。
-- 减小 join_buffer_size 以避免内存压力。建议小于 1% 的内存。
( min( tmp_table_size, max_heap_table_size ) / _ram ) = min( 2147483648, 256M ) / 16384M = 1.6% -- 需要内存时要分配的 RAM 百分比 table （每个 table），或 SELECT 中的温度 table（每个温度 table 每个 SELECTs）。太高可能导致交换。
-- 将 tmp_table_size 和 max_heap_table_size 减少到 ram 的 1%。
( (key_buffer_size - 1.2 * Key_blocks_used * 1024) / _ram ) = (4294967296 - 1.2 * 864035 * 1024) / 16384M = 18.8% -- [= 中浪费的 RAM 百分比101=]。
-- 减少 key_buffer_size
( Key_blocks_used * 1024 / key_buffer_size ) = 864,035 * 1024 / 4294967296 = 20.6% - key_buffer 的使用百分比。高水位线。
-- 降低 key_buffer_size 以避免不必要的内存使用。
( Key_writes / Key_write_requests ) = 7,764,232 / 105012022 = 7.4% -- key_buffer 写入效率
( query_cache_size ) = 1024M -- QC 的大小
-- 太小 = 没有多大用处。太大 = 开销太大。建议0或不超过50M。
( Created_tmp_disk_tables / (Created_tmp_disk_tables + Created_tmp_tables) ) = 2,151,917 / (2151917 + 3928177) = 35.4% -- 溢出的温度百分比 table到磁盘
( tmp_table_size ) = 2,147,483,648 = 2048MB -- 用于支持 SELECT 的 MEMORY temp tables 的大小限制
-- 减少 tmp_table_size 以避免 运行 内存不足。可能不会超过64M。
( back_log / max_connections ) = 50 / 120 = 41.7%
( max_connect_errors ) = 100,000 -- 针对黑客的小保护。
-- 可能不会超过 200。
我有一个使用 mysqls 查询缓存功能的大型数据库应用程序。我想检查查询缓存的内容以识别不应缓存的条目（例如，通过使用 SELECT SQL_NO_CACHE...），因为我想优化我的应用程序。
有没有办法从查询缓存中获取缓存条目的列表？
-- 编辑：Rick 建议的附加信息 ---
1) RAM 大小为 16GB
2) 显示变量；
auto_increment_increment 1
auto_increment_offset 1
autocommit ON
automatic_sp_privileges ON
back_log 50
basedir /usr/
big_tables OFF
binlog_cache_size 32768
binlog_direct_non_transactional_updates OFF
binlog_format STATEMENT
bulk_insert_buffer_size 4294967296
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_general_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 ON
expire_logs_days 0
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/mysqld/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 NO
have_openssl DISABLED
have_partitioning NO
have_query_cache YES
have_rtree_keys YES
have_ssl DISABLED
have_symlink YES
hostname www2
identity 0
ignore_builtin_innodb ON
init_connect
init_file
init_slave
innodb_adaptive_flushing ON
innodb_adaptive_hash_index ON
innodb_additional_mem_pool_size 67108864
innodb_autoextend_increment 8
innodb_autoinc_lock_mode 1
innodb_buffer_pool_size 1073741824
innodb_change_buffering inserts
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_format Antelope
innodb_file_format_check Barracuda
innodb_file_per_table ON
innodb_flush_log_at_trx_commit 1
innodb_flush_method
innodb_force_recovery 0
innodb_io_capacity 200
innodb_lock_wait_timeout 50
innodb_locks_unsafe_for_binlog OFF
innodb_log_buffer_size 67108864
innodb_log_file_size 268435456
innodb_log_files_in_group 2
innodb_log_group_home_dir ./
innodb_max_dirty_pages_pct 75
innodb_max_purge_lag 0
innodb_mirrored_log_groups 1
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innodb_old_blocks_time 0
innodb_open_files 300
innodb_read_ahead_threshold 56
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innodb_rollback_on_timeout OFF
innodb_spin_wait_delay 6
innodb_stats_method nulls_equal
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innodb_stats_sample_pages 8
innodb_strict_mode OFF
innodb_support_xa ON
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innodb_table_locks ON
innodb_thread_concurrency 0
innodb_thread_sleep_delay 10000
innodb_use_sys_malloc ON
innodb_version 1.0.15
innodb_write_io_threads 4
insert_id 0
interactive_timeout 30
join_buffer_size 2147483648
keep_files_on_create OFF
key_buffer_size 4294967296
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 OFF
locked_in_memory OFF
log OFF
log_bin OFF
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log_bin_trust_routine_creators OFF
log_error /var/log/mysql/mysqld.err
log_output FILE
log_queries_not_using_indexes OFF
log_slave_updates OFF
log_slow_queries ON
log_warnings 2
long_query_time 2.000000
low_priority_updates OFF
lower_case_file_system OFF
lower_case_table_names 0
max_allowed_packet 268435456
max_binlog_cache_size 18446744073709547520
max_binlog_size 1073741824
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max_connections 120
max_delayed_threads 20
max_error_count 64
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max_insert_delayed_threads 20
max_join_size 18446744073709551615
max_length_for_sort_data 1024
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max_seeks_for_key 18446744073709551615
max_sort_length 1024
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multi_range_count 256
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myisam_sort_buffer_size 4294967296
myisam_stats_method nulls_unequal
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net_buffer_length 1048576
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new OFF
old OFF
old_alter_table OFF
old_passwords OFF
open_files_limit 8322
optimizer_prune_level 1
optimizer_search_depth 62
optimizer_switch index_merge=on,index_merge_union=on,index_merge_so...
pid_file /var/run/mysqld/mysqld.pid
plugin_dir /usr/lib64/mysql/plugin
port 3306
preload_buffer_size 32768
protocol_version 10
pseudo_thread_id 3468076
query_alloc_block_size 8192
query_cache_limit 4294967296
query_cache_min_res_unit 4096
query_cache_size 1073741824
query_cache_type ON
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query_prealloc_size 8192
rand_seed1
rand_seed2
range_alloc_block_size 4096
read_buffer_size 131072
read_only OFF
read_rnd_buffer_size 8388608
relay_log
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 0
skip_external_locking ON
skip_name_resolve OFF
skip_networking OFF
skip_show_database OFF
slave_compressed_protocol OFF
slave_exec_mode STRICT
slave_load_tmpdir /var/tmp/
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/log/mysql/slowqueries.log
socket /var/run/mysqld/mysqld.sock
sort_buffer_size 262144
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 CEST
table_definition_cache 256
table_lock_wait_timeout 50
table_open_cache 4096
table_type MyISAM
thread_cache_size 16
thread_handling one-thread-per-connection
thread_stack 262144
time_format %H:%i:%s
time_zone SYSTEM
timed_mutexes OFF
timestamp 1449649902
tmp_table_size 2147483648
tmpdir /var/tmp/
transaction_alloc_block_size 8192
transaction_prealloc_size 4096
tx_isolation READ-COMMITTED
unique_checks ON
updatable_views_with_limit YES
version 5.1.56-log
version_comment Gentoo Linux mysql-5.1.56
version_compile_machine x86_64
version_compile_os pc-linux-gnu
wait_timeout 30
warning_count 0
3) 显示全局状态；
Aborted_clients 2094
Aborted_connects 4
Binlog_cache_disk_use 0
Binlog_cache_use 0
Bytes_received 171903979482
Bytes_sent 2515206884666
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Compression OFF
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Threads_cached 14
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Uptime 4656056
Uptime_since_flush_status 4656056
您可以知道使用
缓存的查询数量Show status like 'Qcache_queries_in_cache'
它将在 value 列中为您提供缓存查询的数量。
只有查询的散列存储在 Qcache 中。
无法找到实际缓存了哪些查询。
了解它的一种可能方法是执行您的查询之一并检查 value 列的更改。
如果你有一个 "large" 数据库应用程序，这意味着有很多写入？请记住，当 any 写入 table 时，table 的 all QC 条目将被清除。这意味着您可能无法从 QC 中受益。
此外，清除需要付出努力，从而减慢系统速度。对于query_cache_size下，比如50M，开销不大。但是如果你有1G的QC，你刷QC的时间会比使用QC的时间还长！
无法发现QC 中的实际查询。以下是 可能 的帮助：将 SQL_NO_CACHE 放在任何涉及经常更改的 table(s) 的查询上。将 SQL_CACHE 放在其余部分。然后使用DEMAND。监控 STATUS LIKE Qc%.
如果您想分析您的系统（QC 或其他），请提供 (1) RAM 大小，(2) 显示变量，(3) 在服务器启动至少一天后显示全局状态.
观察：
版本：5.1.56-log
16 GB 内存
正常运行时间 = 53d 21:20:56
您不在 Windows 上 运行。
运行 64 位版本
看来您是 运行 MyISAM 和 InnoDB。
更重要的问题
key_buffer_size = 1500M
innodb_buffer_pool_size = 2000M
join_buffer_size = 1M -- This may be the most important
tmp_table_size = 256M -- Also important
query_cache_size = 50M -- as already mentioned
Use slowlog to find tmp tables spilling to disk
三个设置特别高，可能导致 paging/swapping。 MySQL 性能在 paged/swapped 时受到严重影响。与其发生这种情况，不如降低设置。
细节和小问题
( innodb_buffer_pool_size / _ram ) = 1024M / 16384M = 6.2% -- 用于 InnoDB 的 RAM 百分比 buffer_pool
( Innodb_pages_written / Innodb_buffer_pool_write_requests ) = 29,673,396 / 196667000 = 15.1% -- 必须写入磁盘的写入请求 -- 检查 innodb_buffer_pool_size
( Innodb_buffer_pool_read_ahead_evicted / Innodb_buffer_pool_read_ahead ) = 4,691,916 / 30144135 = 15.6% -- read_ahead 的效用。 -- 关闭预读
( Innodb_os_log_written / (Uptime / 3600) / innodb_log_files_in_group / innodb_log_file_size ) = 34,746,359,296 / (4656056 / 3600) / 2 / 256M = 0.05 -- 比率
( Uptime / 60 * innodb_log_file_size / Innodb_os_log_written ) = 4,656,056 / 60 * 256M / 34746359296 = 599 -- InnoDB 日志轮换之间的分钟数 从 5.6.8 开始，可以动态更改;请务必也更改 my.cnf。 --（轮换间隔 60 分钟的建议有些武断。）
( table_open_cache ) = 4,096 -- 要缓存的 table 个描述符的数量 -- 一般几百就可以了。
( innodb_stats_on_metadata ) = ON -- 触摸统计数据时重新分析 table。 -- ON 可能会减慢某些 SHOW 和 information_schema 访问。
( join_buffer_size ) = 2,147,483,648 = 2048MB -- 每个线程 0-N。可能会加速 JOIN（最好修复 queries/indexes）（所有引擎）用于索引扫描、范围索引扫描、全 table 扫描、每个全 JOIN 等。 -- 使用默认值。
( join_buffer_size / _ram ) = 2,147,483,648 / 16384M = 12.5% -- 每个线程 0-N。可能会加速 JOIN（最好修复 queries/indexes）（所有引擎）用于索引扫描、范围索引扫描、全 table 扫描、每个全 JOIN 等。 -- 减小 join_buffer_size 以避免内存压力。建议小于 1% 的内存。
( min( tmp_table_size, max_heap_table_size ) / _ram ) = min( 2147483648, 256M ) / 16384M = 1.6% -- 需要内存时要分配的 RAM 百分比 table （每个 table），或 SELECT 中的温度 table（每个温度 table 每个 SELECTs）。太高可能导致交换。 -- 将 tmp_table_size 和 max_heap_table_size 减少到 ram 的 1%。
( (key_buffer_size - 1.2 * Key_blocks_used * 1024) / _ram ) = (4294967296 - 1.2 * 864035 * 1024) / 16384M = 18.8% -- [= 中浪费的 RAM 百分比101=]。 -- 减少 key_buffer_size
( Key_blocks_used * 1024 / key_buffer_size ) = 864,035 * 1024 / 4294967296 = 20.6% - key_buffer 的使用百分比。高水位线。 -- 降低 key_buffer_size 以避免不必要的内存使用。
( Key_writes / Key_write_requests ) = 7,764,232 / 105012022 = 7.4% -- key_buffer 写入效率
( query_cache_size ) = 1024M -- QC 的大小 -- 太小 = 没有多大用处。太大 = 开销太大。建议0或不超过50M。
( Created_tmp_disk_tables / (Created_tmp_disk_tables + Created_tmp_tables) ) = 2,151,917 / (2151917 + 3928177) = 35.4% -- 溢出的温度百分比 table到磁盘
( tmp_table_size ) = 2,147,483,648 = 2048MB -- 用于支持 SELECT 的 MEMORY temp tables 的大小限制 -- 减少 tmp_table_size 以避免 运行 内存不足。可能不会超过64M。
( back_log / max_connections ) = 50 / 120 = 41.7%
( max_connect_errors ) = 100,000 -- 针对黑客的小保护。 -- 可能不会超过 200。