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mysql讀操作分為2種類型:snapshot read及current read,前者基于mysql mvcc實現(xiàn),讀取數(shù)據(jù)塊是undo block,后者是基于當(dāng)前數(shù)據(jù)塊。這2種不同的讀取類型與鎖的關(guān)系是什么,本文作一點兒簡要的記錄。
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snapshot read由于操作非當(dāng)前數(shù)據(jù)塊,不會加鎖
x --排它鎖
s --共享鎖
查詢current read不同操作場景持鎖語句
(注:關(guān)注列l(wèi)ock_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)
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