Обсуждение: Testing hot standby on same server sharing same tablespace directory

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Testing hot standby on same server sharing same tablespace directory

От
Sreekanth Palluru
Дата:

 

Hi

 

I am testing hot standby on same server (version 9.5.2) , everything works well. I have a doubt regarding sharing of tablespace directory by these two databases .

I have created a tablespace and moved few objects and I happen to see that same directory was being used by standby node aka slave node and to my surprise it still works without any issues.

 

Is this expected ? I was expecting some sort of warnings from Postgres or am I missing something

 

Master $PGDATA

 

[pg952@pdb-poc01 pg_tblspc]$ pwd

/opt/v9.5.2/data/pg_tblspc

[pg952@pdb-poc01 pg_tblspc]$ ls -ltr

total 0

lrwxrwxrwx. 1 pg952 dba 17 Apr 27 16:10 16495 -> /opt/v9.5.2/tbsp1

[pg952@pdb-poc01 pg_tblspc]$

 

 

I can access the tables

 

 

[pg952@pdb-poc01 pg_tblspc]$ psql -d abcd -p 5432

psql (9.5.2)

Type "help" for help.

 

ssint=# select count(*) from t_random;

  count

---------

8000000

(1 row)

 

ssint=#

 

 

Standby/Slave $PGDATA

 

[pg952@pdb-poc01 pg_tblspc]$ pwd

/home/postgres95/data/pg_tblspc

[pg952@pdb-poc01 pg_tblspc]$ ls -ltr

total 0

lrwxrwxrwx. 1 pg952 dba 17 Apr 27 16:10 16495 -> /opt/v9.5.2/tbsp1

[pg952@pdb-poc01 pg_tblspc]$

 

 

 

[pg952@pdb-poc01 16412]$ psql -d abcd -p 54321

psql (9.5.2)

Type "help" for help.

 

ssint=# delete from t_random;

ERROR:  cannot execute DELETE in a read-only transaction

ssint=# select count(*) from t_random;

  count

---------

8000000

(1 row)

 

ssint=#

 

-Sreekanth

Re: Testing hot standby on same server sharing same tablespace directory

От
Ian Barwick
Дата:
On 04/28/2016 08:45 AM, Sreekanth Palluru wrote:
>
> Hi
>
> I am testing hot standby on same server (version 9.5.2) , everything works well.
> I have a doubt regarding sharing of tablespace directory by these two databases .
>
> I have created a tablespace and moved few objects and I happen to see that same
> directory was being used by standby node aka slave node and to my surprise it still works
> without any issues.
>
> Is this expected ?

Both instances will start and initially appear to function, but you are guaranteed
to run into unexpected behaviour and some kind of corruption.

Try e.g. creating and populating a table, then pausing replay on the standby; then
drop and recreate/repopulate the same table.

> I was expecting some sort of warnings from Postgres or am I missing something

No, there's nothing which could warn about this particular scenario.


Regards

Ian Barwick


--
 Ian Barwick                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


Re: Testing hot standby on same server sharing same tablespace directory

От
Sreekanth Palluru
Дата:
Thanks Ian

-----Original Message-----
From: Ian Barwick [mailto:ian@2ndquadrant.com]
Sent: Thursday, 28 April 2016 11:55 AM
To: Sreekanth Palluru <Sreekanth.Palluru@superchoice.com.au>; pgsql-admin@postgresql.org
Subject: Re: [ADMIN] Testing hot standby on same server sharing same tablespace directory

On 04/28/2016 08:45 AM, Sreekanth Palluru wrote:
>
> Hi
>
> I am testing hot standby on same server (version 9.5.2) , everything works well.
> I have a doubt regarding sharing of tablespace directory by these two databases .
>
> I have created a tablespace and moved few objects and I happen to see
> that same directory was being used by standby node aka slave node and
> to my surprise it still works without any issues.
>
> Is this expected ?

Both instances will start and initially appear to function, but you are guaranteed to run into unexpected behaviour and
somekind of corruption. 

Try e.g. creating and populating a table, then pausing replay on the standby; then drop and recreate/repopulate the
sametable. 

> I was expecting some sort of warnings from Postgres or am I missing
> something

No, there's nothing which could warn about this particular scenario.


Regards

Ian Barwick


--
 Ian Barwick                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services