Re: Serializable read only deferrable- implications

On Tue, Mar 8, 2022 at 9:27 AM Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com>
wrote:

> "PostgreSQL maintains this guarantee even when providing the strictest
> level of transaction isolation through the use of an innovative
> Serializable Snapshot Isolation (SSI) level."
>
> Then:
>
>
> https://www.postgresql.org/docs/current/transaction-iso.html#XACT-SERIALIZABLE
>
> and
>
>
> https://www.postgresql.org/docs/current/applevel-consistency.html#SERIALIZABLE-CONSISTENCY

Thanks to you both. If other concurrent sessions are using default
isolation level of Read committed, would putting long running reports
(read-only) into that read-only serializable deferrable mode be impactful
at all?

The documentation says that a transaction ID is only assigned to a
connection once a write is done, but is the assignment or not of a txn id
actually impactful on anything? I ask partly because it doesn't seem
possible to reset that once assigned, through discard all; or something
else like that which might be used by a connection pooler such as pg
bouncer. is there any way to check if a session has "done writes/updates up
to this point"? It seems pg_my_temp_schema() also returns the same value
even after 'discard temp' or 'discard all' is executed. That was surprising
to me, but would it be considered an issue by anyone?