前言
mysql读操作分为2种类型:snapshot read及current read,前者基于mysql mvcc实现,读取数据块是undo block,后者是基于当前数据块。这2种不同的读取类型与锁的关系是什么，本文作一点儿简要的记录。
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目录
snapshot read是否加锁
snapshot read由于操作非当前数据块，不会加锁
current read加锁2种类型
x --排它锁
s --共享锁
current read几种操作场景
查询current read不同操作场景持锁语句（注：关注列lock_mode）
mysql> select * from information_schema.innodb_locks; +-------------------------+-----------------+-----------+-----------+------------------+-----------------+------------+-----------+----------+----------------+ | lock_id | lock_trx_id | lock_mode | lock_type | lock_table | lock_index | lock_space | lock_page | lock_rec | lock_data | +-------------------------+-----------------+-----------+-----------+------------------+-----------------+------------+-----------+----------+----------------+ | 11909:473:3:2 | 11909 | X | RECORD | `zxydb`.`t_read` | GEN_CLUST_INDEX | 473 | 3 | 2 | 0x00000836F561 | | 421207096970864:473:3:2 | 421207096970864 | S | RECORD | `zxydb`.`t_read` | GEN_CLUST_INDEX | 473 | 3 | 2 | 0x00000836F561 | +-------------------------+-----------------+-----------+-----------+------------------+-----------------+------------+-----------+----------+----------------+ 2 rows in set, 1 warning (0.00 sec)
