Обсуждение: what causes new temp schemas to be created

When a temp table is created I see a pg_temp_NNN (for example
pg_temp_3, pg_toast_temp_3) schemas created when/why are additional
temp schemas created( pg_temp_4/pg_toast_temp_4)?

Ted

On Mon, Jul 10, 2023 at 7:18 AM Ted Toth <txtoth@gmail.com> wrote:

When a temp table is created I see a pg_temp_NNN (for example
pg_temp_3, pg_toast_temp_3) schemas created when/why are additional
temp schemas created( pg_temp_4/pg_toast_temp_4)?

Temporary schemas are isolated to the session they are created in.  Hence, you get multiple temporary schemas if you have concurrent sessions using temporary objects.

I don't see that the schema is removed when the session is over and I
see other sessions come along later and use it. I'm assuming here that
a session is started on connect and ended when the connection is
closed.

On Mon, Jul 10, 2023 at 9:21 AM David G. Johnston
<david.g.johnston@gmail.com> wrote:
>
> On Mon, Jul 10, 2023 at 7:18 AM Ted Toth <txtoth@gmail.com> wrote:
>>
>> When a temp table is created I see a pg_temp_NNN (for example
>> pg_temp_3, pg_toast_temp_3) schemas created when/why are additional
>> temp schemas created( pg_temp_4/pg_toast_temp_4)?
>>
>
> Temporary schemas are isolated to the session they are created in.  Hence, you get multiple temporary schemas if you
haveconcurrent sessions using temporary objects. 
>
> David J.

So it's an optimization to reuse existing but currently unused temp
schemas, correct?

On Mon, Jul 10, 2023 at 11:22 AM David G. Johnston
<david.g.johnston@gmail.com> wrote:
>
> On Mon, Jul 10, 2023 at 9:20 AM Ted Toth <txtoth@gmail.com> wrote:
>>
>> I don't see that the schema is removed when the session is over and I
>> see other sessions come along later and use it. I'm assuming here that
>> a session is started on connect and ended when the connection is
>> closed.
>>
>
> The first time a session needs a temporary schema it is assigned one which is then immediately cleared out.
>
> David J.

Ted Toth <txtoth@gmail.com> writes:
> So it's an optimization to reuse existing but currently unused temp
> schemas, correct?

Exactly.  We could just destroy and recreate the old temp schema,
but that seems to lead to useless catalog churn.  Instead we just
destroy any old contents, if there's an existing temp schema in
the slot assigned to the current backend.

            regards, tom lane