Thread: Hot standby documentation

Hot standby documentation

From
Joshua Tolley
Date:
Having concluded I really need to start playing with hot standby, I started
looking for documentation on the subject. I found what I was looking for; I
also found this page[1], which, it seems, ought to mention hot standby.
Comments?

[1] http://developer.postgresql.org/pgdocs/postgres/high-availability.html

--
Joshua Tolley / eggyknap
End Point Corporation
http://www.endpoint.com

Re: Hot standby documentation

From
Fujii Masao
Date:
On Thu, Jan 7, 2010 at 6:09 PM, Joshua Tolley <eggyknap@gmail.com> wrote:
> Having concluded I really need to start playing with hot standby, I started
> looking for documentation on the subject. I found what I was looking for; I
> also found this page[1], which, it seems, ought to mention hot standby.
> Comments?
>
> [1] http://developer.postgresql.org/pgdocs/postgres/high-availability.html

+1

At least, it should be mentioned that the slave can answer
read-only queries in "Warm Standby Using Point-In-Time Recovery".
And so "Table 25-1" should be changed.

Regards,

-- 
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center


Re: Hot standby documentation

From
Simon Riggs
Date:
On Thu, 2010-01-07 at 18:34 +0900, Fujii Masao wrote:
> On Thu, Jan 7, 2010 at 6:09 PM, Joshua Tolley <eggyknap@gmail.com> wrote:
> > Having concluded I really need to start playing with hot standby, I started
> > looking for documentation on the subject. I found what I was looking for; I
> > also found this page[1], which, it seems, ought to mention hot standby.
> > Comments?
> >
> > [1] http://developer.postgresql.org/pgdocs/postgres/high-availability.html
> 
> +1
> 
> At least, it should be mentioned that the slave can answer
> read-only queries in "Warm Standby Using Point-In-Time Recovery".
> And so "Table 25-1" should be changed.

OK, will add.

-- Simon Riggs           www.2ndQuadrant.com



Re: Hot standby documentation

From
Bruce Momjian
Date:
Joshua Tolley wrote:
-- Start of PGP signed section.
> Having concluded I really need to start playing with hot standby, I started
> looking for documentation on the subject. I found what I was looking for; I
> also found this page[1], which, it seems, ought to mention hot standby.
> Comments?
> 
> [1] http://developer.postgresql.org/pgdocs/postgres/high-availability.html

Ah, I now realize it only mentions "warm" standby, not "hot", so I just
updated the documentation to reflect that;  you can see it here:
http://momjian.us/tmp/pgsql/high-availability.html
Warm and Hot Standby Using Point-In-Time Recovery (PITR)

Do we want to call the feature "hot standby"?  Is a read-only standby a
"standby" or a "slave"?

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + If your life is a hard drive, Christ can be your backup. +


Re: Hot standby documentation

From
Markus Wanner
Date:
Bruce,

Bruce Momjian wrote:
> Ah, I now realize it only mentions "warm" standby, not "hot", so I just
> updated the documentation to reflect that;  you can see it here:

Maybe the table below also needs an update, because unlike "Warm Standby 
using PITR", a hot standby accepts read-only queries and can be 
configured to not loose data on master failure.

> Do we want to call the feature "hot standby"?  Is a read-only standby a
> "standby" or a "slave"?

I think hot standby is pretty much the term, now.

Regards

Markus Wanner


Re: Hot standby documentation

From
Robert Haas
Date:
On Sun, Feb 7, 2010 at 4:41 AM, Markus Wanner <markus@bluegap.ch> wrote:
> Bruce Momjian wrote:
>> Do we want to call the feature "hot standby"?  Is a read-only standby a
>> "standby" or a "slave"?
>
> I think hot standby is pretty much the term, now.

See here for the previous iteration of this discussion:

http://archives.postgresql.org/pgsql-hackers/2009-08/msg00870.php

I've always thought this feature was misnamed and nothing has happened
to change my mind, but it's not clear whether I'm in the majority.

...Robert


Re: Hot standby documentation

From
Josh Berkus
Date:
> I've always thought this feature was misnamed and nothing has happened
> to change my mind, but it's not clear whether I'm in the majority.

I'm afraid force of habit is more powerful than correctness on this one.It's going to be HS/SR whether that's perfectly
corrector not.
 

--Josh Berkus



Re: Hot standby documentation

From
"David E. Wheeler"
Date:
On Feb 7, 2010, at 12:35 PM, Josh Berkus wrote:

>> I've always thought this feature was misnamed and nothing has happened
>> to change my mind, but it's not clear whether I'm in the majority.
>
> I'm afraid force of habit is more powerful than correctness on this one.
> It's going to be HS/SR whether that's perfectly correct or not.

What would be correct? I thought HS/SR were pretty correct (as long as no one confuses SR with synchronous
replication!).

Best,

David




Re: Hot standby documentation

From
Bruce Momjian
Date:
Markus Wanner wrote:
> Bruce,
> 
> Bruce Momjian wrote:
> > Ah, I now realize it only mentions "warm" standby, not "hot", so I just
> > updated the documentation to reflect that;  you can see it here:
> 
> Maybe the table below also needs an update, because unlike "Warm Standby 
> using PITR", a hot standby accepts read-only queries and can be 
> configured to not loose data on master failure.

Ahh, good point.  I had not considered the table would change.  What I
did was to mark "Slaves accept read-only queries" as "Hot only".  You
can see the result here:
http://momjian.us/tmp/pgsql/high-availability.html

I did not change "Master failure will never lose data" because the 9.0
streaming implementation is not sychronous (see wal_sender_delay in
postgresql.conf), and I don't think even setting that to zero makes the
operation synchronous.  I think we will have to wait for PG 9.1 for
_synchronous_ streaming replication.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + If your life is a hard drive, Christ can be your backup. +


Re: Hot standby documentation

From
Fujii Masao
Date:
On Mon, Feb 8, 2010 at 10:34 PM, Bruce Momjian <bruce@momjian.us> wrote:
> Ahh, good point.  I had not considered the table would change.  What I
> did was to mark "Slaves accept read-only queries" as "Hot only".

Can the "warm standby" still reside in v9.0? If not, the mark of
"Hot only" seems odd for me.

> I did not change "Master failure will never lose data" because the 9.0
> streaming implementation is not sychronous (see wal_sender_delay in
> postgresql.conf), and I don't think even setting that to zero makes the
> operation synchronous.  I think we will have to wait for PG 9.1 for
> _synchronous_ streaming replication.

You are right.

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center


Re: Hot standby documentation

From
Bruce Momjian
Date:
Fujii Masao wrote:
> On Mon, Feb 8, 2010 at 10:34 PM, Bruce Momjian <bruce@momjian.us> wrote:
> > Ahh, good point. ?I had not considered the table would change. ?What I
> > did was to mark "Slaves accept read-only queries" as "Hot only".
> 
> Can the "warm standby" still reside in v9.0? If not, the mark of
> "Hot only" seems odd for me.

Yes, both hot and warm standby is supported in 9.0.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + If your life is a hard drive, Christ can be your backup. +