Hot standby documentation

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

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

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. +

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

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

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.

--Josh Berkus

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

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. +

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

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. +