在事务内创建数据库 [英] CREATE DATABASE inside transaction

问题描述

根据 postgresql 文档；

According to postgresql docs;

CREATE DATABASE cannot be executed inside a transaction block.

这有技术原因吗?

推荐答案

当你尝试时，你得到错误:

When you try it, you get the error:

ERROR:  CREATE DATABASE cannot run inside a transaction block

这来自 src/backend/access/transam/xact.c(我的资料中的第 3023 行，但因版本而异)，在 PreventTransactionChain(...).

This comes from src/backend/access/transam/xact.c (line 3023 on my sources, but varies by version), in PreventTransactionChain(...).

那里的评论解释说:

此例程将由不得在内部运行的语句调用一个事务块，通常是因为它们具有不可回滚副作用或进行内部提交.

This routine is to be called by statements that must not run inside a transaction block, typically because they have non-rollback-able side effects or do internal commits.

对于CREATE DATABASE，它是从src/backend/tcop/utility.c 在standard_ProcessUtility 中调用的T_CreatedbStmt，但不幸的是，没有任何内容丰富的评论说明为什么 CREATE DATABASE 在事务中运行不安全.

For CREATE DATABASE it's called from src/backend/tcop/utility.c in standard_ProcessUtility under the case for T_CreatedbStmt, but unfortunately there isn't any informative comment that says why specifically CREATE DATABASE isn't safe to run in a transaction.

查看消息来源，我可以看到，一方面它会强制设置检查点.

Looking at the sources, I can see that for one thing it forces a checkpoint.

不过，总的来说，我没有看到任何真正大喊我们不能以交易方式执行此操作"的内容.更多的是我们还没有实现以事务方式执行此操作的功能".

Overall, though, I don't see anything that really screams out "we can't do this transactionally". It's more "we haven't implemented the functionality to do this transactionally".

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