mysql - 大型MyISAM表中的MySQL基本更新查询太慢(MySQL basic update query in large-ish MyISAM table too slow)

Question

UPDATE SomeTable SET X = null, Y = null in a (61 million rows, 6.4 GB, MyISAM) table takes about 55 minutes .

(UPDATE SomeTable SET X = null, Y = null （在6100万行，6.4 GB，MyISAM表中） UPDATE SomeTable SET X = null, Y = null大约需要55分钟 。)

(MySQL 5.7, Windows 10 on i7 laptop, mains cable plugged in, MySQL running at about 30% CPU).

(（MySQL 5.7，i7笔记本电脑上的Windows 10，已插入电源线，MySQL运行约30％的CPU）。)

Columns X and Y are not part of any index.

(X和Y列不属于任何索引。)

(I needed to run this query to null some previously entered erroneous data.)

(（我需要运行此查询以使一些以前输入的错误数据为空。）)

But: ALTER TABLE SomeTable ADD COLUMN X FLOAT NULL DEFAULT NULL, ADD COLUMN Y FLOAT NULL DEFAULT NULL , which requires a complete read/write of table plus index takes only about 15 minutes.

(但是： ALTER TABLE SomeTable ADD COLUMN X FLOAT NULL DEFAULT NULL, ADD COLUMN Y FLOAT NULL DEFAULT NULL ，这需要对表和索引进行完整的读/写操作仅花费约15分钟。)

What is the problem here?

(这里有什么问题？)

  ask by Matthias Otto translate from so

Answer 1

等待大神答复