Thank you very much, got it.
> On 28 Dec 2018, at 11:36 PM, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> wrote:
>
> Hello
>
> On 2018-Dec-28, ZongtianHou wrote:
>
>> I get somehow confused when I learn about namespace here, there are two questions,
>> First, what is the difference between namespace and schema?
>
> None. Schema is the user-visible name for the feature; namespace is the
> source code and system catalog level.
>
>> Second, why the Oid of public namespace is 2200, the same between
>> databases?
>
> Not necessarily. That's the initial value, but it's possible to drop
> the public schema and create it afresh.
>
>> Does oid is unique for every object across cluster?
>
> No, only inside each individual catalog are OIDs guaranteed unique.
>
>> Does someone know about these clearly?
>
> Yes.
>
> --
> Álvaro Herrera https://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
>