Обсуждение: Unique cluster / instance identifier?

Hi all;


Does PostgreSQL store a unique cluster or instance identifier that we 
can access to identify our instances?


Thanks in advance

S. Bob

Monday, February 18, 2019 12:08 PM

Hi all;


Does PostgreSQL store a unique cluster or instance identifier that we can access to identify our instances?


Thanks in advance

>>>>> "S" == S Bob <sbob@quadratum-braccas.com> writes:

 S> Hi all;

 S> Does PostgreSQL store a unique cluster or instance identifier that
 S> we can access to identify our instances?

Yes. But it's not easy to get at: it's the "Database system identifier"
shown in the output of pg_controldata. (pg12+ will have a function to
get it from SQL, but released versions don't.)

e.g.

Database system identifier:           6659016342798875639

The number is mostly generated from the time the instance was created,
with some bits modified. So for example:

$ perl -le 'print scalar gmtime +(shift >> 32)' 6659016342798875639
Sun Feb 17 17:04:21 2019

PG uses this internally to make sure that replication never tries to
apply WAL records generated on one system to a different system.
Physical replication secondary systems share the primary's system
identifier since they always originate as a copy (via base backup) of
the primary.

-- 
Andrew (irc:RhodiumToad)

Perfect!  Thanks


On 2/18/19 11:03 AM, Andrew Gierth wrote:
>>>>>> "S" == S Bob <sbob@quadratum-braccas.com> writes:
>   S> Hi all;
>
>   S> Does PostgreSQL store a unique cluster or instance identifier that
>   S> we can access to identify our instances?
>
> Yes. But it's not easy to get at: it's the "Database system identifier"
> shown in the output of pg_controldata. (pg12+ will have a function to
> get it from SQL, but released versions don't.)
>
> e.g.
>
> Database system identifier:           6659016342798875639
>
> The number is mostly generated from the time the instance was created,
> with some bits modified. So for example:
>
> $ perl -le 'print scalar gmtime +(shift >> 32)' 6659016342798875639
> Sun Feb 17 17:04:21 2019
>
> PG uses this internally to make sure that replication never tries to
> apply WAL records generated on one system to a different system.
> Physical replication secondary systems share the primary's system
> identifier since they always originate as a copy (via base backup) of
> the primary.
>

Andrew Gierth

Monday, February 18, 2019 1:03 PM

S> Hi all;

S> Does PostgreSQL store a unique cluster or instance identifier that
S> we can access to identify our instances?

Yes. But it's not easy to get at: it's the "Database system identifier"
shown in the output of pg_controldata. (pg12+ will have a function to
get it from SQL, but released versions don't.)

e.g.

Database system identifier: 6659016342798875639

The number is mostly generated from the time the instance was created,
with some bits modified. So for example:

$ perl -le 'print scalar gmtime +(shift >> 32)' 6659016342798875639
Sun Feb 17 17:04:21 2019

PG uses this internally to make sure that replication never tries to
apply WAL records generated on one system to a different system.
Physical replication secondary systems share the primary's system
identifier since they always originate as a copy (via base backup) of
the primary.

S. Bob

Monday, February 18, 2019 12:08 PM

Hi all;


Does PostgreSQL store a unique cluster or instance identifier that we can access to identify our instances?


Thanks in advance

On 2/18/19 1:03 PM, Andrew Gierth wrote:
>>>>>> "S" == S Bob <sbob@quadratum-braccas.com> writes:
>
>  S> Hi all;
>
>  S> Does PostgreSQL store a unique cluster or instance identifier that
>  S> we can access to identify our instances?
>
> Yes. But it's not easy to get at: it's the "Database system identifier"
> shown in the output of pg_controldata. (pg12+ will have a function to
> get it from SQL, but released versions don't.)

Umm, that function has been there since pg 9.6

select left(version(),17), system_identifier from pg_control_system();
       left        |  system_identifier
-------------------+---------------------
 PostgreSQL 9.6.11 | 6320270156373568679
(1 row)

Joe

--
Crunchy Data - http://crunchydata.com
PostgreSQL Support for Secure Enterprises
Consulting, Training, & Open Source Development

>>>>> "Joe" == Joe Conway <mail@joeconway.com> writes:

 Joe> Umm, that function has been there since pg 9.6

my mistake, you are of course correct

-- 
Andrew (irc:RhodiumToad)