1、read_buffer_size 缓存连续扫描的块,这个缓存是跨存储引擎的,不只是MyISAM表。 2、sort_buffer_size 执行排序缓存区的大小,最好将其设置为1M-2M,然后在会话中设置,为一个特定的查询设置更高的值。 3、join_buffer_size 执行联合查询分配的缓存区大小,将其设置为1M-2M大小,然后在每个会话中再单独按需设置。
1.文件排序,使用sort命令: sort --buffer-size=1G --output=/path/to/output /path/to/src_file # --buffer-size在Debian上可用,其他平台未知,不是标准参数. 并集:sort -m /path/to/src1 /path/tosrc2 -u --output=/path/to/result # 注意src1, src2必须是已排序的文件,而且结果也是已排序的。
六、分组(group by)优化 group by 的优化策略和order by 的优化策略非常像,主要列举如下几个要点: group by 即使没有过滤条件用到索引,也可以直接使用索引; group by 先排序再分组,遵照索引建的最佳左前缀法则; 当无法使用索引列时,增大 max_length_for_sort_data 和 sort_buffer_size 参数的设置; where效率...
SET@@GLOBAL.sort_buffer_size=50000,sort_buffer_size=1000000; System Variable References in Expressions To refer to the value of a system variable in expressions, use one of the@@-modifiers. For example, you can retrieve system variable values in aSELECTstatement like this: ...
1.文件排序,使用sort命令: sort --buffer-size=1G --output=/path/to/output /path/to/src_file # --buffer-size在Debian上可用,其他平台未知,不是标准参数. 并集:sort -m /path/to/src1 /path/tosrc2 -u --output=/path/to/result # 注意src1, src2必须是已排序的文件,而且结果也是已排序的。
Status:ClosedImpact on me: None Category:MySQL Server: DocumentationSeverity:S3 (Non-critical) Version:5.1OS:Any Assigned to:Paul DuBoisCPU Architecture:Any [8 Jan 2009 10:21] Horst Hunger Description:Values set for "sort_buffer_size" are rounded to other values, which is not described in th...
4. sort_buffer_size = 256K 5. loose-innodb_log_files_in_group = 2 The following variables were set to non-default values previously but have been modified such that they are now set to the server default values: 1. key_buffer_size = 1M ...
公共参数 max_connections = 151 #同时处理最大连接数,推荐设置最大连接数是上限连接数的80%左右 sort_buffer_size = 2M #查询排序时缓冲区大小,只对order...1024 #打开文件数限制,如果show global status like 'open_files'查看的值等于或者大于open_files_limit值时,程序会无法连接数据库或卡死 MyISAM参数....
// stage 4. store the first min(total,linesMax) lines to the output buffer lines_max = std::min(lines_max, (int) _sort_buf.size()); double scale = 1. / (rho_num + 2); for (i = 0; i < lines_max; i++) { LinePolar line{}; ...
# sort_buffer_size = 2M # read_rnd_buffer_size = 2M datadir=/var/lib/mysql socket=/var/lib/mysql/mysql.sock # Disabling symbolic-links is recommended to prevent assorted security risks symbolic-links=0 log-error=/var/log/mysqld.log ...