Shulou(Shulou.com)06/01 Report--

Preface

There are two types of mysql read operations: snapshot read and current read. The former is based on mysql mvcc, the read data block is undo block, and the latter is based on the current data block. This article gives a brief account of the relationship between these two different read types and locks.

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Whether the directory snapshot read is locked

Snapshot read will not lock because the operation is not the current data block.

Two types of current read lock

X-exclusive lock

S-shared lock

Several operating scenarios of current read

Query current read lock-holding statements in different operation scenarios

(note: follow column 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 | +- -- +- -+ | 119090x00000836F561 4730x00000836F561 2 | 11909 | X | RECORD | `zxydb`.`t _ read` | GEN_CLUST_INDEX | 473 | 3 | 2 | 0x00000836F561 | 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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