(1)sort 算子,会显示排序信息 Sort Method代表排序的方法,包括quicksort(快排)和disksort(外排)。快排即内存够用时,所有的排序操作均在内存中完成,外排说明当前可用内存不足,需要下盘。 (2)hashjoin算子 Buckets:代表hash表中实际使用的桶的个数 Batches:代表hashjoin中实际分块的数量。如果Batches=1,则说明所有...
这个filesort是说, MySQL要多做一次额外的排序, 确切的说是快速排序(Quicksort). 先初步了解下Quicksort排序的概念(From Wikipedia). Quicksort is a divide and conquer algorithm. Quicksort first divides a large array into two smaller sub-arrays: the low elements and the high elements. Quicksort can ...
about MySQL5.7.20 初始数据:world.sql 现在,让我们回想一下SQL的执行过程: 客户端将SQL发送到mysqld。 经过连接层。 在SQL层,会经过、语法、语意检查、权限检查后经过解析器预处理后,产生计划(可能产生多个执行计划),优化器根据解析器得出的多种执行计划,选择一个最优执行计划,然后执行器执行SQL产生执行结果。
tmp_fanout= cur_fanout= (double) table->quick_rows[key]; }else{// Check if we have statistic about the distributionif(keyinfo->has_records_per_key(cur_used_keyparts -1)) { cur_fanout= keyinfo->records_per_key(cur_used_keyparts -1);if(!table_deps && table->quick_keys.is_set(k...
table_deps && //(C1) table->quick_key_parts[key] == cur_used_keyparts && //(C2) table->quick_n_ranges[key] == 1+MY_TEST(ref_or_null_part)) //(C3) { tmp_fanout= cur_fanout= (double) table->quick_rows[key]; } else { // Check if we have statistic about the ...
(actual time=0.143..0.145 rows=10 loops=1) Output: students.studentid, students.firstname, students.lastname, enrollments.coursename, enrollments.grade Sort Key: students.studentid, enrollments.coursename Presorted Key: students.studentid Full-sort Groups: 1 Sort Method: quicksort Average Memory:...
table->quick_key_parts[key] == cur_used_keyparts && //(C2) table->quick_n_ranges[key] == 1+MY_TEST(ref_or_null_part)) //(C3) { tmp_fanout= cur_fanout= (double) table->quick_rows[key]; } else { // Check if we have statistic about the distribution ...
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Thethumbs upandthumbs downicons at the top of the page are provided so you can provide feedback about the visual and the feature. Doing so provides feedback, but it doesn't currently train the algorithm to influence the results returned next time you use the feature. ...
If we take the green beam to be the reference beam, we'd subject the blue beam to some sort of change we wanted to measure. The interferometer combines the two beams and the interference fringes that appear on the screen are a visual representation of the difference between them. When the...