更新删除期间的postgres死锁

Question

我遇到死锁错误，现在想了解这种情况。

假设我有一个带有主键ID的表。 我有另一个表b，其列为parent_a_id，child_a_id。 外键约束是：

"b_parent_id_fkey" FOREIGN KEY (parent_a_id) REFERENCES a(id) ON DELETE CASCADE
"b_child_id_fkey" FOREIGN KEY (child_a_id) REFERENCES a(id) ON DELETE CASCADE

当我运行以下两个查询时，将出现死锁情况

update a set some_field = 0 where id = $1
delete from a where id = $1

这是postgres日志：

ERROR:  deadlock detected
DETAIL:  Process 28165 waits for ShareLock on transaction 112624590; blocked by process 20900.
Process 20900 waits for ShareLock on transaction 112624583; blocked by process 28165.
Process 28165: update a set some_field = 0 where id = $1
Process 20900: delete from a where id = $1