mysql snapshot read快照讀及current read當前讀與鎖lock之一
前言
mysql讀操作分為2種型別:snapshot read及current read,前者基於mysql mvcc實現,讀取資料塊是undo block,後者是基於當前資料塊。這2種不同的讀取型別與鎖的關係是什麼,本文作一點兒簡要的記錄。
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目錄
snapshot read是否加鎖
snapshot read由於操作非當前資料塊,不會加鎖
current read加鎖2種型別
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x --排它鎖
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s --共享鎖
current read幾種操作場景
查詢current read不同操作場景持鎖語句
(注:關注列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)
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