Re: [bug fix] Savepoint-related statements terminates connection

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Simon Riggs <simon(at)2ndquadrant(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, "Tsunakawa, Takayuki" <tsunakawa(dot)takay(at)jp(dot)fujitsu(dot)com>, Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [bug fix] Savepoint-related statements terminates connection
Date: 2017-09-03 22:20:17
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I wrote:
> ... PFA a patch
> that invents a notion of an "implicit" transaction block.

On further consideration, I think the control logic I added in
exec_simple_query() is a shade bogus. I set it up to only force
an implicit transaction block when there are at least two statements
remaining to execute. However, that has the result of allowing, eg,

begin\; select 1\; commit\; vacuum;

Now in principle it's perfectly OK to allow that, since the vacuum
is alone in its transaction. But it feels more like an implementation
artifact than a good design. The existing code doesn't allow it,
and we might have a hard time duplicating this behavior if we ever
significantly rewrote the transaction infrastructure. Plus I'd hate
to have to explain it to users. I think we'd be better off enforcing
transaction block restrictions on every statement in a multi-command
string, regardless of the location of any COMMIT/ROLLBACK within the

Hence, attached a v2 that does it like that. I also fully reverted
4f896dac1 by undoing its changes to PreventTransactionChain; other
than that, the changes in xact.c are the same as before.

regards, tom lane

Attachment Content-Type Size
introduce-implicit-transaction-blocks-2.patch text/x-diff 24.8 KB

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