postgresql - Postgres 的可序列化事务阻塞并发写

Question

在PostgreSQL's isolation levels documentation据称

To guarantee true serializability PostgreSQL uses predicate locking, which means that it keeps locks which allow it to determine when a write would have had an impact on the result of a previous read from a concurrent transaction, had it run first. In PostgreSQL these locks do not cause any blocking and therefore can not play any part in causing a deadlock. They are used to identify and flag dependencies among concurrent Serializable transactions which in certain combinations can lead to serialization anomalies.

当我尝试在隔离级别 SERIALIZABLE 中执行两个更新语句时，似乎第二个写入阻塞，直到第一个事务提交或中止。你可以看到 gif 文件中的交互:

about 语句如何解释这种行为？我希望第二个事务一直持续到提交，然后得到 could not serialize 错误。

顺便说一句，event 表的架构如下:

CREATE TABLE event (
  id INT,
  created_at timestamp
)

Answer 1

该段落仅描述谓词锁，它是一类特殊的锁，仅用于可序列化隔离级别。

除了这些特殊的锁之外，可序列化的事务还会使用其他隔离级别使用的“普通”锁。