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 = 1000000, SESSION sort_buffer_size = 1000000; SET @@GLOBAL.sort_buffer_size = 1000000, @@LOCAL.sort_buffer_size = 1000000; SET GLOBAL max_connections = 1000, sort_buffer_size = 1000000; The @@GLOBAL., @@PERSIST., @@PERSIST_ONLY., @@SESSION., and @@ ...
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。
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: ...
实现方式是先将须要排序的字段和可以直接定位到相关行数据的指针信息取出,然后在设定的内存(通过参数sort_buffer_size设定)中进行排序,完成排序之后再次通过行指针信息取出所需的Columns。 注:该算法是4.1之前采用的算法,它需要两次访问数据,尤其是第二次读取操作会导致大量的随机I/O操作。另一方面,内存开销较小。
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...
// 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 ...
gss_release_buffer(3GSS) gss_release_cred(3GSS) gss_release_name(3GSS) gss_release_oid(3GSS) gss_release_oid_set(3GSS) gss_store_cred(3GSS) gss_str_to_oid(3GSS) gss_test_oid_set_member(3GSS) gss_unwrap(3GSS) gss_verify_mic(3GSS) gss_wrap(3GSS) gss_wrap_size_limit(3GSS)...