MySQL performance monitoring and SQL statements

1、 The query cache ：

mysql> show variables like '%query_cache%';

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2、 cached Cache Number of threads in thread_cache_size：

　mysql> show variables like 'thread%';

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3、DB Number of threads connected ：

mysql> show status like 'connections';

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4、 Current connection thread status ：

mysql> show status like '%thread%';

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5、 Index cache size ：

mysql> show variables like 'key_buffer_size';

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6、 Index cache miss rate ：

mysql> show global status like 'key_read%';

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7、 Index cache hit rate ：

mysql> show global status like 'key_%';

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8、 Index read Statistics ：

mysql> show global status like 'key_blocks_u';

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key_blocks_unused Represents an unused cache cluster （blocks） Count ,key_blocks_used That's the largest that's ever been used blocks, If the cache is used , Either increase key_buffer_size, Or over indexing , The cache is full .

9、 Maximum concurrent connections - Maximum connections allowed （ commonly 500 To 800 More appropriate ）：

mysql> show variables like 'max_connections';

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10、 Maximum concurrent connections - The server responded to the maximum number of connections ：

mysql> show global status like 'max_used_connections';

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11、 Maximum concurrent connections - Current connections ：

mysql> show global status like 'connections';

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12、 Maximum concurrent connections - The thread queue （ The smaller the value, the better ）：

mysql> show variables like 'back_log';

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13、 A temporary table ：

mysql> show global status like 'created_tmp%';

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The temporary table is too large to use disk files when the memory is completed , If 'created_tmp_tables A very large , There may be too many sorting operations in the system , Or the table connection method is not optimized enough .

14、mysql Server configuration of temporary tables ：

mysql> show variables where variable_name  in ('temp_able_siae','max_heap_table_size');

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When the temporary table space is smaller than max_heap_table_size when , Can all be put into memory .

15、 Table scan ：

mysql> show global status like 'handler_read%';
mysql> show global status like 'com_select';

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If the table scan rate exceeds 4000, Description too many table scans , Maybe the index is not built , increase read_buffer_size Value will be good , But don't check 8M.