Will insert be locked? If it's locked, what's the point?
Update and delete in innodb will implicitly add exclusive lock,
update table set... where id in (1,2,3,4); What is the exclusive lock? Add these four records directly, or lock, modify and commit in sequence according to the ID;
Will delete and update implicitly add write locks?
Will select implicitly add a read lock?
If it is added in two situations, both are table lock levels, then the concurrency is particularly bad, right?
Choice of two engines
MyISAM: If you execute a large number of SELECTs, MyISAM is a better choice. Why is this? I actually tested 3.6 million pieces of data, all of which used index selection. Innodb is much more efficient.
InnoDB: If your data performs a large number of INSERT or UPDATE, you should use an InnoDB table. Is this because of the myisam table lock?
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谢邀。
InnoDB
InnoDB对
INSERT可能只锁表头吧，总之不会锁全表的；UPDATE(如果没有FOR UPDATE或LOCK IN SHARE MODE)和DELETE在执行时会加写锁，有时就是锁全表，所以会影响并发性能，但这只是一瞬间的事，所以并发不高的情况下往往看不出来；一次
UPDATE多行，肯定是多行一起锁，提交后一起释放的，因为MySQL要保证这条语句的原子性，当一条有主键冲突时，其他的也都不能提交了。MySQL
UPDATE和DELETE都会加写锁，而且锁全表；SELECT会加读锁，所以多个SELECT可以并发，但不能和UPDATE、DELETE并发；INSERT的加锁有点特殊，锁的强度可能介于读锁和写锁之间，与SELECT、INSERT可以并发。最后，MyISAM就
SELECT而言性能不会比InnoDB好很多，这还取决于行的存储方式，比如MyISAM的FIXED可能会比DYNAMIC快一些。另外，你的这个例子肯定会对InnoDB更有利些：如果改成一个非主键的索引，那么InnoDB未必会那么快；如果只SELECT id这一列，那么MyISAM未必这么慢。其中的道理可以搜一下聚集索引。