源码

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};

前置知识

每开启一个事务，数据库会自动为之分配一个tx_id，它是线性增长的，也就是越后开启的事务，tx_id越大。

trx_ids

Additional trx ids which the read should not see: typically, these are the read-write active transactions at the time when the read is serialized, except the reading transaction itself; the trx ids in this array are in a descending order. These trx_ids should be between the "low" and "high" water marks, that is, up_limit_id and low_limit_id.

创建该read view 时活跃的事务id数组，不包含创建该read view的事务id（except the reading transaction itself）。

low_limit_id

The smallest number not yet assigned as a transaction id or transaction number

活跃id的最大值+1。虽然是low，但数值确实最大的， 其实就是max_trx_id

up_limit_id

活跃事务id的最小值，最早创建的事务的id，其实就是min_trx_id。

creator_trx_id

创建该read view的事务id