我在 Ubuntu 18.04 上有 MySQL 5.7.23。这是一个具有 2 个 vCore 和 8 GiB RAM 的 VPS。该服务器托管两个 WordPress 网站。每个网站都有一个大小为 7.5 MB 的数据库。所以总共有 15 MB 的数据库。
我试图使用mysqltuner优化数据库。它每次都向我推荐同样的事情：
Variables to adjust:
tmp_table_size (> 64M)
max_heap_table_size (> 64M)
我从 16M 开始，然后我被建议将值增加到 32M，现在它建议我将值增加到 64M 或更多。但为什么？我所有数据库的总大小约为 15M。
我有足够的内存，可用内存约为 6.5 GiB，因此我可以为 MySQL 使用更多内存。
来自 mysqltuner 的完整日志是
root@web:~# perl mysqltuner.pl
>> MySQLTuner 1.7.10 - Major Hayden <major@mhtx.net>
>> Bug reports, feature requests, and downloads at http://mysqltuner.com/
>> Run with '--help' for additional options and output filtering
[--] Skipped version check for MySQLTuner script
[OK] Logged in using credentials from Debian maintenance account.
[OK] Currently running supported MySQL version 5.7.23-0ubuntu0.18.04.1
[OK] Operating on 64-bit architecture
-------- Log file Recommendations ---------------------------------------------- --------------------
[--] Log file: /var/log/mysql/error.log(0B)
[OK] Log file /var/log/mysql/error.log exists
[OK] Log file /var/log/mysql/error.log is readable.
[!!] Log file /var/log/mysql/error.log is empty
[OK] Log file /var/log/mysql/error.log is smaller than 32 Mb
[OK] /var/log/mysql/error.log doesn't contain any warning.
[OK] /var/log/mysql/error.log doesn't contain any error.
[--] 0 start(s) detected in /var/log/mysql/error.log
[--] 0 shutdown(s) detected in /var/log/mysql/error.log
-------- Storage Engine Statistics --------------------------------------------- --------------------
[--] Status: +ARCHIVE +BLACKHOLE +CSV -FEDERATED +InnoDB +MEMORY +MRG_MYISAM +My ISAM +PERFORMANCE_SCHEMA
[--] Data in InnoDB tables: 14.2M (Tables: 45)
[OK] Total fragmented tables: 0
-------- Security Recommendations ---------------------------------------------- --------------------
[OK] There are no anonymous accounts for any database users
[OK] All database users have passwords assigned
[--] Bug #80860 MySQL 5.7: Avoid testing password when validate_password is acti vated
-------- CVE Security Recommendations ------------------------------------------ --------------------
[--] Skipped due to --cvefile option undefined
-------- Performance Metrics --------------------------------------------------- --------------------
[--] Up for: 1d 2h 43m 42s (84K q [0.879 qps], 1K conn, TX: 441M, RX: 12M)
[--] Reads / Writes: 98% / 2%
[--] Binary logging is disabled
[--] Physical Memory : 7.8G
[--] Max MySQL memory : 384.4M
[--] Other process memory: 252.8M
[--] Total buffers: 224.0M global + 1.1M per thread (151 max threads)
[--] P_S Max memory usage: 72B
[--] Galera GCache Max memory usage: 0B
[OK] Maximum reached memory usage: 228.3M (2.86% of installed RAM)
[OK] Maximum possible memory usage: 384.4M (4.82% of installed RAM)
[OK] Overall possible memory usage with other process is compatible with memory available
[OK] Slow queries: 0% (0/84K)
[OK] Highest usage of available connections: 2% (4/151)
[OK] Aborted connections: 0.00% (0/1561)
[OK] Query cache is disabled by default due to mutex contention on multiprocesso r machines.
[OK] Sorts requiring temporary tables: 0% (0 temp sorts / 12K sorts)
[OK] No joins without indexes
[!!] Temporary tables created on disk: 44% (3K on disk / 7K total)
[OK] Thread cache hit rate: 99% (4 created / 1K connections)
[OK] Table cache hit rate: 77% (1K open / 1K opened)
[OK] Open file limit used: 1% (56/5K)
[OK] Table locks acquired immediately: 100% (202 immediate / 202 locks)
-------- Performance schema ---------------------------------------------------- --------------------
[--] Memory used by P_S: 72B
[--] Sys schema is installed.
-------- ThreadPool Metrics ---------------------------------------------------- --------------------
[--] ThreadPool stat is disabled.
-------- MyISAM Metrics -------------------------------------------------------- --------------------
[!!] Key buffer used: 18.3% (3M used / 16M cache)
[OK] Key buffer size / total MyISAM indexes: 16.0M/43.0K
[OK] Read Key buffer hit rate: 96.3% (190 cached / 7 reads)
-------- InnoDB Metrics -------------------------------------------------------- --------------------
[--] InnoDB is enabled.
[--] InnoDB Thread Concurrency: 0
[OK] InnoDB File per table is activated
[OK] InnoDB buffer pool / data size: 128.0M/14.2M
[OK] Ratio InnoDB log file size / InnoDB Buffer pool size: 16.0M * 2/128.0M shou ld be equal 25%
[OK] InnoDB buffer pool instances: 1
[--] Number of InnoDB Buffer Pool Chunk : 1 for 1 Buffer Pool Instance(s)
[OK] Innodb_buffer_pool_size aligned with Innodb_buffer_pool_chunk_size & Innodb _buffer_pool_instances
[OK] InnoDB Read buffer efficiency: 99.96% (2124360 hits/ 2125302 total)
[!!] InnoDB Write Log efficiency: 83.91% (9286 hits/ 11067 total)
[OK] InnoDB log waits: 0.00% (0 waits / 1781 writes)
-------- AriaDB Metrics -------------------------------------------------------- --------------------
[--] AriaDB is disabled.
-------- TokuDB Metrics -------------------------------------------------------- --------------------
[--] TokuDB is disabled.
-------- XtraDB Metrics -------------------------------------------------------- --------------------
[--] XtraDB is disabled.
-------- RocksDB Metrics ------------------------------------------------------- --------------------
[--] RocksDB is disabled.
-------- Spider Metrics -------------------------------------------------------- --------------------
[--] Spider is disabled.
-------- Connect Metrics ------------------------------------------------------- --------------------
[--] Connect is disabled.
-------- Galera Metrics -------------------------------------------------------- --------------------
[--] Galera is disabled.
-------- Replication Metrics --------------------------------------------------- --------------------
[--] Galera Synchronous replication: NO
[--] No replication slave(s) for this server.
[--] Binlog format: ROW
[--] XA support enabled: ON
[--] Semi synchronous replication Master: Not Activated
[--] Semi synchronous replication Slave: Not Activated
[--] This is a standalone server
-------- Recommendations ------------------------------------------------------- --------------------
General recommendations:
When making adjustments, make tmp_table_size/max_heap_table_size equal
Reduce your SELECT DISTINCT queries which have no LIMIT clause
Variables to adjust:
tmp_table_size (> 64M)
max_heap_table_size (> 64M)