From: Tom Lane <tgl@sss.pgh.pa.us>
To: Heikki Linnakangas <hlinnaka@iki.fi>
cc: "Wirch, Eduard" <eduard.w@smart-host.com>,
        pgsql-hackers@lists.postgresql.org
Subject: Re: PostgreSql: Canceled on conflict out to old pivot
In-reply-to: <590f3e4d-a561-43aa-b4a6-ee72387af275@iki.fi>
References: <CAPX+m-hdbj4b1Ufcpx+YAGj8BLF91gdi6zr0Pc3NKZTBDtKUrQ@mail.gmail.com> <4cf7082a-23d0-4e9a-87b8-9c336b55f6c5@iki.fi> <CAPX+m-jF52dHkve0et0WAScC2JkELChdmxVUNbTCrDM0oq903Q@mail.gmail.com> <590f3e4d-a561-43aa-b4a6-ee72387af275@iki.fi>
Comments: In-reply-to Heikki Linnakangas <hlinnaka@iki.fi>
	message dated "Fri, 01 Dec 2023 01:35:09 +0200"
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Date: Thu, 30 Nov 2023 18:51:35 -0500
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Heikki Linnakangas <hlinnaka@iki.fi> writes:
> On 30/11/2023 18:24, Wirch, Eduard wrote:
>> My understanding of serializable isolation is that only transactions
>> which can somehow affect each other can conflict. It should be clear
>> for PostgreSql, that transactions belonging to different databases
>> cannot affect each other. Why do they cause serializable conflicts?

On what grounds do you assert that?  Operations on shared catalogs
are visible across databases.  Admittedly they can't be written by
ordinary DML, and I'm not sure that we make any promises about DDL
writes honoring serializability.  But I'm unwilling to add
"optimizations" that assume that that will never happen.

			regards, tom lane