This problem seems to have been solved in v15 and v16. Because of this patch (12d768e70497afc5a57acf73c251316997b5175a), the use of static variables has been cancelled. But this problem can obviously be reproduced on v14(and perhaps v12 v13). Try the following SQL again.
START TRANSACTION ISOLATION LEVEL SERIALIZABLE; COMMIT AND CHAIN; COMMIT ;
START TRANSACTION ISOLATION LEVEL SERIALIZABLE; COMMIT ;
START TRANSACTION ISOLATION LEVEL REPEATABLE READ; savepoint s; COMMIT AND CHAIN;
SHOW transaction_isolation; -- transaction is active at this point
COMMIT;
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发件人：Laurenz Albe<laurenz.albe@cybertec.at>
日 期：2023年09月21日 14:41:20
收件人：刘相(佑熙)<evan.lx@alibaba-inc.com>; <pgsql-bugs@lists.postgresql.org>
主 题：Re: BUG #18118: bug report for COMMIT AND CHAIN feature
On Wed, 2023-09-20 at 09:31 +0000, PG Bug reporting form wrote:
> PostgreSQL version: 14.9
> Operating system: centos7
> Description:
>
> COMMIT(280a408b48d5ee42969f981bceb9e9426c3a344c) provides a way to support
> chained commits. During recent development, I found that it left a flaw.
>
> The defect can be reproduced as follows:
>
> START TRANSACTION ISOLATION LEVEL SERIALIZABLE; COMMIT;
> START TRANSACTION ISOLATION LEVEL REPEATABLE READ\; savepoint s\; COMMIT AND
> CHAIN;
> SHOW transaction_isolation; -- transaction is active at this point
> COMMIT;
>
> will get:
> postgres=*# SHOW transaction_isolation; -- transaction is active at this
> point
> transaction_isolation
> -----------------------
> serializable
> (1 row)
I tried to reproduce that and failed, both with v14 and v16.
For me, "transaction_isolation" is "repeatable read".
Yours,
Laurenz Albe