Re: Proposal for Implenting read-only queries during wal replay (SoC 2007)

Hi

I plan to submit a proposal for implementing support for
read-only queries during wal replay as a "Google Summer of Code 2007"
project.

I've been browsing the postgres source-code for the last few days,
and came up with the following plan for a implementation.

I'd be very interested in any feedback on the propsoal - especially
of the "you overlooked this an that, it can never work that way" kind ;-)

greetings, Florian Pflug

Implementing read-only quries during wal archive replay
-------------------------------------------------------

Submitter: Florian Pflug <fgp(at)phlo(dot)org>

Abstract:
Implementing full support for read-only queries during
wal archive replay is splitted into multiple parts, where
each part offeres additional functionality over what
postgres provides now. This makes tackling this as a
"Google Summer of Code 2007" project feasable, and guarantees
that at least some progress is made, even if solving the
whole problem turns out to be harder then previously
thought.

Parts/Milestones of the implementation:
A) Allow postgres to be started in read-only mode. After
initial wal recovery, postgres doesn't perform writes
anymore. All transactions started are implicitly in
readonly mode. All transactions will be assigned dummy
transaction ids, which never make it into the clog.
B) Split StartupXLOG into two steps. The first (Recovery) will process
only enough wal to bring the system into a consistent state,
while the second one (Replay) replays the archive until it finds no
more wal segments. This replay happens in chunks, such that
after a chunk all *_safe_restartpoint functions return true.
C) Combine A) and B), in the simplest possible way.
Introduce a global R/W lock, which is taken by the Replay part
of B) in write mode before replaying a chunk, then released,
and immediatly reaquired before replaying the next chunk.
The startup sequence is modified to do only the Recovery part
where is is doing StartupXLOG now, and to lauch an extra process
(similar to bgwriter) to do the second (Replay) part in the background.
The system is then started up in read-only mode, with the addition
that the global R/W lock is taken in read mode before starting any
transaction. Thus, while a transaction is running, no archive replay
happens.

Benefits:
*) Part A) alone might be of value for some people in the embedded world,
or people who want to distribute software the use postgres. You could
e.g. distribute a CD with a large, read-only database, and your application
would just need to start postmaster to be able to query it directly from
the CD.
*) Read-only hot standby is a rather simple way to do load-balancing, if
your application doesn't depend on the data being absolutely up-to-date.
*) Even if this isn't used for load-balancing, it gives the DBA an
easy way to check how far a PITR slave is lagging behind, therefore
making PITR replication more user-friendly.

Open Questions/Problems
*) How do read-only transactions obtain a snapshot? Is it sufficient
to just create an "empty" snapshot for them, meaning that they'll
always look at the clog to obtain a transaction's state?
*) How many places to attempt to issue writes? How hard is it to
silence them all while in read-only mode.
*) How does the user interface look like? I'm currently leaning towards
a postgresql.conf setting read_only=yes. This would put postgres
into read-only mode, and if a recovery.conf is present, archive
replay would run as a background process.

Limitations:
*) The replaying process might be starved, letting the slave fall
further and further behind the master. Only true if the slave
executes a lot of queries, though.
*) Postgres would continue to run in read-only mode, even after finishing
archive recovery. A restart would be needed to switch it into read-write
mode again. (I probably wouldn't be too hard to do that switch without
a restart, but it seems better to tackle this after the basic features
are working)

Hi,
Here's some feedback, this is a feature that would be very useful to a
project I am currently working on.

Doug

On Fri, 2007-02-23 at 17:34 +0100, Florian G. Pflug wrote:
> Hi
>
> I plan to submit a proposal for implementing support for
> read-only queries during wal replay as a "Google Summer of Code 2007"
> project.
>
> I've been browsing the postgres source-code for the last few days,
> and came up with the following plan for a implementation.
>
> I'd be very interested in any feedback on the propsoal - especially
> of the "you overlooked this an that, it can never work that way" kind ;-)
>
> greetings, Florian Pflug
>
> Implementing read-only quries during wal archive replay
> -------------------------------------------------------
>
> Submitter: Florian Pflug <fgp(at)phlo(dot)org>
>
> Abstract:
> Implementing full support for read-only queries during
> wal archive replay is splitted into multiple parts, where
> each part offeres additional functionality over what
> postgres provides now. This makes tackling this as a
> "Google Summer of Code 2007" project feasable, and guarantees
> that at least some progress is made, even if solving the
> whole problem turns out to be harder then previously
> thought.
>
> Parts/Milestones of the implementation:
> A) Allow postgres to be started in read-only mode. After
> initial wal recovery, postgres doesn't perform writes
> anymore. All transactions started are implicitly in
> readonly mode. All transactions will be assigned dummy
> transaction ids, which never make it into the clog.
> B) Split StartupXLOG into two steps. The first (Recovery) will process
> only enough wal to bring the system into a consistent state,
> while the second one (Replay) replays the archive until it finds no
> more wal segments. This replay happens in chunks, such that
> after a chunk all *_safe_restartpoint functions return true.
> C) Combine A) and B), in the simplest possible way.
> Introduce a global R/W lock, which is taken by the Replay part
> of B) in write mode before replaying a chunk, then released,
> and immediatly reaquired before replaying the next chunk.
> The startup sequence is modified to do only the Recovery part
> where is is doing StartupXLOG now, and to lauch an extra process
> (similar to bgwriter) to do the second (Replay) part in the background.
> The system is then started up in read-only mode, with the addition
> that the global R/W lock is taken in read mode before starting any
> transaction. Thus, while a transaction is running, no archive replay
> happens.
>
> Benefits:
> *) Part A) alone might be of value for some people in the embedded world,
> or people who want to distribute software the use postgres. You could
> e.g. distribute a CD with a large, read-only database, and your application
> would just need to start postmaster to be able to query it directly from
> the CD.
> *) Read-only hot standby is a rather simple way to do load-balancing, if
> your application doesn't depend on the data being absolutely up-to-date.
> *) Even if this isn't used for load-balancing, it gives the DBA an
> easy way to check how far a PITR slave is lagging behind, therefore
> making PITR replication more user-friendly.
>
> Open Questions/Problems
> *) How do read-only transactions obtain a snapshot? Is it sufficient
> to just create an "empty" snapshot for them, meaning that they'll
> always look at the clog to obtain a transaction's state?
> *) How many places to attempt to issue writes? How hard is it to
> silence them all while in read-only mode.
> *) How does the user interface look like? I'm currently leaning towards
> a postgresql.conf setting read_only=yes. This would put postgres
> into read-only mode, and if a recovery.conf is present, archive
> replay would run as a background process.
>
> Limitations:
> *) The replaying process might be starved, letting the slave fall
> further and further behind the master. Only true if the slave
> executes a lot of queries, though.
> *) Postgres would continue to run in read-only mode, even after finishing
> archive recovery. A restart would be needed to switch it into read-write
> mode again. (I probably wouldn't be too hard to do that switch without
> a restart, but it seems better to tackle this after the basic features
> are working)
>
> ---------------------------(end of broadcast)---------------------------
> TIP 5: don't forget to increase your free space map settings
>

"Florian G. Pflug" <fgp(at)phlo(dot)org> writes:
> I plan to submit a proposal for implementing support for
> read-only queries during wal replay as a "Google Summer of Code 2007"
> project.

You are discussing this on the wrong list.

> B) Split StartupXLOG into two steps. The first (Recovery) will process
> only enough wal to bring the system into a consistent state,

How will you know what that is?

> C) Combine A) and B), in the simplest possible way.
> Introduce a global R/W lock, which is taken by the Replay part
> of B) in write mode before replaying a chunk, then released,
> and immediatly reaquired before replaying the next chunk.

That seems certain to result in intolerable performance, for both the
queries and the replay process.

regards, tom lane

Tom Lane wrote:
> "Florian G. Pflug" <fgp(at)phlo(dot)org> writes:
>> I plan to submit a proposal for implementing support for
>> read-only queries during wal replay as a "Google Summer of Code 2007"
>> project.
>
> You are discussing this on the wrong list.
So what list would be more appropriate?

>> B) Split StartupXLOG into two steps. The first (Recovery) will process
>> only enough wal to bring the system into a consistent state,
>
> How will you know what that is?
With the same logic that postgres uses now to bring an file-system backup
into a consistent state when doing PITR.

>> C) Combine A) and B), in the simplest possible way.
>> Introduce a global R/W lock, which is taken by the Replay part
>> of B) in write mode before replaying a chunk, then released,
>> and immediatly reaquired before replaying the next chunk.
>
> That seems certain to result in intolerable performance, for both the
> queries and the replay process.

That depends entirely on the usecase. And besides, this limitation could
and probably would be adressed in the future. I think a step-by-step
approach is more likely to be successfull then attempting to solve
all problems at once.

greetings, Florian Pflug

"Florian G. Pflug" <fgp(at)phlo(dot)org> writes:
> Tom Lane wrote:
>> You are discussing this on the wrong list.

> So what list would be more appropriate?

My mistake, I read the message header and saw "Postgresql-General" ...
did not look at the actual address ...

regards, tom lane

Florian G. Pflug wrote:
> I plan to submit a proposal for implementing support for
> read-only queries during wal replay as a "Google Summer of Code 2007"
> project.
>
> I've been browsing the postgres source-code for the last few days,
> and came up with the following plan for a implementation.
>
> I'd be very interested in any feedback on the propsoal - especially
> of the "you overlooked this an that, it can never work that way" kind ;-)

I had the same thought roughly two years ago:

http://archives.postgresql.org/pgsql-hackers/2005-11/msg01043.php

People weren't very interested in having a read-only mode. I think it
would be a nice feature if it's not too complicated.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com

I'll throw in my vote, I would find this quite useful.

-Glen

> Florian G. Pflug wrote:
>> I plan to submit a proposal for implementing support for
>> read-only queries during wal replay as a "Google Summer of Code 2007"
>> project.
>>
>> I've been browsing the postgres source-code for the last few days,
>> and came up with the following plan for a implementation.
>>
>> I'd be very interested in any feedback on the propsoal - especially
>> of the "you overlooked this an that, it can never work that way" kind ;-)

> People weren't very interested in having a read-only mode. I think it
> would be a nice feature if it's not too complicated.

Actually, I think there's high demand for it off this list. Effectively it
would allow our "warm backup mode" to become a "hot backup mode". As SoC
admin, I'd vote for such a proposal unless someone explains to me why it's
impossible.

--
--Josh

Josh Berkus
PostgreSQL @ Sun
San Francisco

Josh Berkus wrote:
>> People weren't very interested in having a read-only mode. I think it
>> would be a nice feature if it's not too complicated.
>
> Actually, I think there's high demand for it off this list. Effectively it
> would allow our "warm backup mode" to become a "hot backup mode". As SoC
> admin, I'd vote for such a proposal unless someone explains to me why it's
> impossible.

One thing I would like noted, is whoever does SoC work for PostgreSQL
this year, needs to work *with* the community. Otherwise there is no point.

A good example of the wrong way to do it is the Full Disjunctions
project. Great idea, Great project, not bitrot and hard space because it
hasn't been touched or maintained sense release.

In order to get it into core, it would have needed a lot of work. Let's
make sure we don't duplicate the issue.

Joshua D. Drake

--

=== The PostgreSQL Company: Command Prompt, Inc. ===
Sales/Support: +1.503.667.4564 || 24x7/Emergency: +1.800.492.2240
Providing the most comprehensive PostgreSQL solutions since 1997
http://www.commandprompt.com/

Donate to the PostgreSQL Project: http://www.postgresql.org/about/donate
PostgreSQL Replication: http://www.commandprompt.com/products/

On Fri, Feb 23, 2007 at 10:57:24PM +0000, Heikki Linnakangas wrote:
> Florian G. Pflug wrote:
> >I plan to submit a proposal for implementing support for
> >read-only queries during wal replay as a "Google Summer of Code 2007"
> >project.
> >
> >I've been browsing the postgres source-code for the last few days,
> >and came up with the following plan for a implementation.
> >
> >I'd be very interested in any feedback on the propsoal - especially
> >of the "you overlooked this an that, it can never work that way" kind ;-)
>
> I had the same thought roughly two years ago:
>
> http://archives.postgresql.org/pgsql-hackers/2005-11/msg01043.php
>
> People weren't very interested in having a read-only mode. I think it
> would be a nice feature if it's not too complicated.

Every customer I've ever talked to about HA has either asked about it or
thought it was a great idea. We should definitely do it if it's not a
load of difficult..
--
Jim Nasby jim(at)nasby(dot)net
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)

Heikki Linnakangas wrote:
> Florian G. Pflug wrote:
>> I plan to submit a proposal for implementing support for
>> read-only queries during wal replay as a "Google Summer of Code 2007"
>> project.
>>
>> I've been browsing the postgres source-code for the last few days,
>> and came up with the following plan for a implementation.
>>
>> I'd be very interested in any feedback on the propsoal - especially
>> of the "you overlooked this an that, it can never work that way" kind ;-)
>
> I had the same thought roughly two years ago:
>
> http://archives.postgresql.org/pgsql-hackers/2005-11/msg01043.php
>
> People weren't very interested in having a read-only mode. I think it
> would be a nice feature if it's not too complicated.

I think "main" feature would be supporting read-only queries on PITR
slaves. But creating a read-only mode seemed to me (and to you too, it
seems ;-) ) like a good first step towards that goal.

After reading tom's reply to your original proposal, I agree that
supporting a write-protected datadir is not a true subset of
supporting read-only queries on PITR slaves. But I still think
that tackling the read-only datadir support is a good first step -
not the least because it'll help me to get familiar with the
relevent parts of the backend.

I've been thinking about your "trick" of writing "readonly" into
the postmaster.pid file to switch postgres into read-only mode.
On the one hand, it's really neat - if solves the problem of not
being able to create a pid file in the datadir in ro mode, while
on the other hand making sure that there *is* a pid file. But
if I went that way, it would mean there would be *three* configfiles
you have to get right for a working PITR slave with read-only query
support - postgresql.conf, recovery.conf, and postmaster.pid.

So I think I'll rather go with a postgresql.conf setting. I'd
allow three values "hard", "soft" and "off".
"hard" would prevent all writes to the datadir, while
"soft" would be the setting of choice for a PITR slave.

In the "soft" case, postgres would still write a postmaster.pid,
and so be protected against other running postmasters.
In the "hard" case, there would be no such protection - but since
there would be no writes anyway, you don't risk data corruption
in case another postmaster was running - the worst the would happen
is that the read-only postmaster crashes.

greetings, Florian Pflug

Josh Berkus wrote:
>> People weren't very interested in having a read-only mode. I think it
>> would be a nice feature if it's not too complicated.
>
> Actually, I think there's high demand for it off this list. Effectively it
> would allow our "warm backup mode" to become a "hot backup mode". As SoC
> admin, I'd vote for such a proposal unless someone explains to me why it's
> impossible.

From my point of view, the most subtle point of the whole proposal is
if not doing
wal-replay _and_ quries at the same time, but rather one after the other,
really solves all the locking issues.

My line of reasoning is that stopping wal replay at a arbitrary point,
and then starting a read-only transaction with an "empty snapshot" (meaning
that all exactly those transactions marked as comitted in the clog are
assumed to be visible to the transaction) is exactly the same as sending
the backend a SIGKILL when it just wrote the wal record in question,
and then restarting postgres, and starting a transaction.

Since later won't lead to problems today, doing the formed for hot standby
should not lead to problems too.

There reason that I put "Process wal in chucks such that all
*_safe_restartpoint" functions return true at the end of a chunk" was
the be on the safe side, not because I could find any actual problem
if that requirement was dropped.

Can anyone find a flaw in those arguments?

greetings, Florian Pflug

"Florian G. Pflug" <fgp(at)phlo(dot)org> writes:
> My line of reasoning is that stopping wal replay at a arbitrary point,
> and then starting a read-only transaction with an "empty snapshot" (meaning
> that all exactly those transactions marked as comitted in the clog are
> assumed to be visible to the transaction) is exactly the same as sending
> the backend a SIGKILL when it just wrote the wal record in question,
> and then restarting postgres, and starting a transaction.

The hole in that reasoning is that no one would be satisfied with the
behavior of a Postgres database that was being forcibly restarted every
few seconds. Yeah, we won't lose transactions that have been promised
committed, but losing a large fraction of transactions-in-progress won't
please anyone. Nor will queries on a slave that's behaving like that
provide an accurate model of what the same queries would produce if issued
on the master.

regards, tom lane

Tom Lane wrote:
> "Florian G. Pflug" <fgp(at)phlo(dot)org> writes:
>> My line of reasoning is that stopping wal replay at a arbitrary point,
>> and then starting a read-only transaction with an "empty snapshot" (meaning
>> that all exactly those transactions marked as comitted in the clog are
>> assumed to be visible to the transaction) is exactly the same as sending
>> the backend a SIGKILL when it just wrote the wal record in question,
>> and then restarting postgres, and starting a transaction.
>
> The hole in that reasoning is that no one would be satisfied with the
> behavior of a Postgres database that was being forcibly restarted every
> few seconds. Yeah, we won't lose transactions that have been promised
> committed, but losing a large fraction of transactions-in-progress won't
> please anyone. Nor will queries on a slave that's behaving like that
> provide an accurate model of what the same queries would produce if issued
> on the master.

Sorry, I don't get your point. What do you mean by "loosing a large
fraction of transactions in progress". You wouldn't loose them - the
master would be running as usual. And after the slave replayed the
wal past their commit record, they would be visible on the slave too.
The point of my argument was just to convice (myself) that wal-logging of
locking requests is not necessary, as long as you don't want to playback
archived wal _and_ run read-only queries on the slave at the same time.

I also don't understand what you mean by "Nor will queries on the slave
that's behaving like that provide an accurate model of what the same
queries would produce if issued on the master". Sureley they won't -
after all, this is a kind of asynchronous replication. The most
you can hope fore is to eventually catch up with the master.

And I don't propose that my serialization of wal-replay and running
queries is how PITR master-slave replication should ultimatly look
like. But's it's something that can be done _now_, without changing
what kind of operations are wal-logged. And something that I believe
I can finish in the timeframe of a SoC project.

After I'm done with implementing this limited read-only mode, I'd be very
interested in trying to extend it, by allow wal-replay and queries
to run concurrently.

greetings, Florian Pflug

On 2/23/07, Joshua D. Drake <jd(at)commandprompt(dot)com> wrote:
> A good example of the wrong way to do it is the Full Disjunctions
> project. Great idea, Great project, not bitrot and hard space because it
> hasn't been touched or maintained sense release.

Don't get me started there. The decision was split between PostgreSQL
core 50/50 for inclusion in contrib, yet it was not included. As I
said at the time, people will move on and the project would go to
pgfoundry (which I called the graveyard) and die; which is exactly
what happened. And, in the Full Disjunctions project's defense, the
community was wholly at fault. He posted several times for
suggestions and most of the community responses were, "why would we
care about or want that."

The community can't rely on contributors, especially students, to
spend months of their time pushing ideas through a gauntlet of
negativity.

--
Jonah H. Harris, Software Architect | phone: 732.331.1324
EnterpriseDB Corporation | fax: 732.331.1301
33 Wood Ave S, 3rd Floor | jharris(at)enterprisedb(dot)com
Iselin, New Jersey 08830 | http://www.enterprisedb.com/

Jonah H. Harris wrote:
> On 2/23/07, Joshua D. Drake <jd(at)commandprompt(dot)com> wrote:
>> A good example of the wrong way to do it is the Full Disjunctions
>> project. Great idea, Great project, not bitrot and hard space because it
>> hasn't been touched or maintained sense release.
>
> Don't get me started there. The decision was split between PostgreSQL
> core 50/50 for inclusion in contrib, yet it was not included.

The argument for not including it was valid, it didn't adhere on several
levels including code style and grammatical changes.

The point is, if the author would have done the project in public, the
problem wouldn't have happen.

> As I
> said at the time, people will move on and the project would go to
> pgfoundry (which I called the graveyard) and die;

I would say that is the author's fault. There are plenty of extremely
vibrant and lively developed projects on pgfoundry.

>which is exactly
> what happened. And, in the Full Disjunctions project's defense, the
> community was wholly at fault. He posted several times for
> suggestions and most of the community responses were, "why would we
> care about or want that."

Yes *some* of the community didn't understand it but there were others
in the community who made a specific effort to explain why it was good,
including Josh Berkus.

>
> The community can't rely on contributors, especially students, to
> spend months of their time pushing ideas through a gauntlet of
> negativity.
>

Someone who wants to provide a feature to the community can't expect the
community just to open their arms without explanation and full
discussion of a feature.

You don't honestly expect a mature open source project to just accept
any code do you?

For the record, I like the idea of full disjunctions but they must past
quality muster to be included in the community.

Joshua D. Drake

--

=== The PostgreSQL Company: Command Prompt, Inc. ===
Sales/Support: +1.503.667.4564 || 24x7/Emergency: +1.800.492.2240
Providing the most comprehensive PostgreSQL solutions since 1997
http://www.commandprompt.com/

Donate to the PostgreSQL Project: http://www.postgresql.org/about/donate
PostgreSQL Replication: http://www.commandprompt.com/products/

On 2/24/07, Joshua D. Drake <jd(at)commandprompt(dot)com> wrote:
> The argument for not including it was valid, it didn't adhere on several
> levels including code style and grammatical changes.

IIRC, the only exception to code style was cleaning up some mixed
code/declaration warnings.

> The point is, if the author would have done the project in public, the
> problem wouldn't have happen.

It was public, very few offered suggestions.

> I would say that is the author's fault. There are plenty of extremely
> vibrant and lively developed projects on pgfoundry.

He already did over a year and half research on the subject, wrote the
code for it, published a paper on it, and offered it to the community.
Why would he choose to spend more time getting beaten up for
something that's already behind him?

> Yes *some* of the community didn't understand it but there were others
> in the community who made a specific effort to explain why it was good,
> including Josh Berkus.

Yes, there were a few.

> Someone who wants to provide a feature to the community can't expect the
> community just to open their arms without explanation and full
> discussion of a feature.

Perhaps you don't recall.. but his design and research was far more
than almost all other PostgreSQL features. The only one longer was
perhaps the HOT design.

> You don't honestly expect a mature open source project to just accept
> any code do you?

Obviously not. That's just a stupid question to ask.

> For the record, I like the idea of full disjunctions but they must past
> quality muster to be included in the community.

Again, he offered to fix anything anyone had issues with... but people
were too busy whining about the feature itself than to provide sound
advice for moving forward.

--
Jonah H. Harris, Software Architect | phone: 732.331.1324
EnterpriseDB Corporation | fax: 732.331.1301
33 Wood Ave S, 3rd Floor | jharris(at)enterprisedb(dot)com
Iselin, New Jersey 08830 | http://www.enterprisedb.com/

> He already did over a year and half research on the subject, wrote the
> code for it, published a paper on it, and offered it to the community.
> Why would he choose to spend more time getting beaten up for
> something that's already behind him?

If he is not willing to proceed with public debate, I fail to see the
purpose in doing the work at all.

> Perhaps you don't recall.. but his design and research was far more
> than almost all other PostgreSQL features. The only one longer was
> perhaps the HOT design.

Hmmm and look at HOT. That would be an example of how it *should* be
done. HOT has been a constant influx of WIP patches and discussion *to
the community* and thusly to rounding out nicely to be a great feature.

Full Disjunctions did not do that.

>> For the record, I like the idea of full disjunctions but they must past
>> quality muster to be included in the community.
>
> Again, he offered to fix anything anyone had issues with... but people

Then why didn't he fix them? There were specific problems people had.

> were too busy whining about the feature itself than to provide sound
> advice for moving forward.
>

Guess we will have to agree to disagree. That is not my recollection of
the events on any level.

Sincerely,

Joshua D. Drake

--

=== The PostgreSQL Company: Command Prompt, Inc. ===
Sales/Support: +1.503.667.4564 || 24x7/Emergency: +1.800.492.2240
Providing the most comprehensive PostgreSQL solutions since 1997
http://www.commandprompt.com/

Donate to the PostgreSQL Project: http://www.postgresql.org/about/donate
PostgreSQL Replication: http://www.commandprompt.com/products/

On 2/24/07, Joshua D. Drake <jd(at)commandprompt(dot)com> wrote:
> Guess we will have to agree to disagree. That is not my recollection of
> the events on any level.

Guess so. This topic ended in August and I'm no longer going to argue about it.

--
Jonah H. Harris, Software Architect | phone: 732.331.1324
EnterpriseDB Corporation | fax: 732.331.1301
33 Wood Ave S, 3rd Floor | jharris(at)enterprisedb(dot)com
Iselin, New Jersey 08830 | http://www.enterprisedb.com/

Jonah H. Harris wrote:
> On 2/23/07, Joshua D. Drake <jd(at)commandprompt(dot)com> wrote:
> > A good example of the wrong way to do it is the Full Disjunctions
> > project. Great idea, Great project, not bitrot and hard space because it
> > hasn't been touched or maintained sense release.
>
> Don't get me started there. The decision was split between PostgreSQL
> core 50/50 for inclusion in contrib, yet it was not included. As I
> said at the time, people will move on and the project would go to
> pgfoundry (which I called the graveyard) and die; which is exactly
> what happened. And, in the Full Disjunctions project's defense, the
> community was wholly at fault. He posted several times for
-----------------------------
> suggestions and most of the community responses were, "why would we
> care about or want that."
>
> The community can't rely on contributors, especially students, to
> spend months of their time pushing ideas through a gauntlet of
> negativity.

Jonah, I have no idea what "fault" you are trying to blame on the
community in the above statement. The author didn't discuss the idea
with the community before spending months on it so we have no obligation
to accept it in the core.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://www.enterprisedb.com

+ If your life is a hard drive, Christ can be your backup. +

On 2/26/07, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> Jonah, I have no idea what "fault" you are trying to blame on the
> community in the above statement. The author didn't discuss the idea
> with the community before spending months on it so we have no obligation
> to accept it in the core.

You're missing the point entirely. The majority of the (vocal)
community didn't even want the feature and as such, failed to provide
viable suggestions for him to move forward. As the majority of the
community didn't want the feature, it wouldn't have made a difference
when he proposed it; which would have remained negative nonetheless.

--
Jonah H. Harris, Software Architect | phone: 732.331.1324
EnterpriseDB Corporation | fax: 732.331.1301
33 Wood Ave S, 3rd Floor | jharris(at)enterprisedb(dot)com
Iselin, New Jersey 08830 | http://www.enterprisedb.com/

Jonah H. Harris wrote:
> On 2/26/07, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>> Jonah, I have no idea what "fault" you are trying to blame on the
>> community in the above statement. The author didn't discuss the idea
>> with the community before spending months on it so we have no obligation
>> to accept it in the core.
>
> You're missing the point entirely. The majority of the (vocal)
> community didn't even want the feature and as such, failed to provide
> viable suggestions for him to move forward. As the majority of the
> community didn't want the feature, it wouldn't have made a difference
> when he proposed it; which would have remained negative nonetheless.

There are so many things wrong with the above paragraph. Vocal hackers?

Bruce, wanted real world example
Dave, wanted it in contrib
Berkus, wanted it in contrib
Drake, (not really a hacker) pushed for exposure even though pushed to
pgfoundry
Tgl, wanted real world example, backed it on pgfoundry
Dunstan, liked the idea but wanted it pushed to pgfoundry

From what I can tell Jonah, you are all bark and no bite. Everything you
mention is bogus in this thread. I read the responses (just now) about
full disjunctions and they were not negative. They were more, "Show me
the beef" which is perfectly acceptable when reviewing the possibility
of accepting code.

From what I can tell, unless the hacker said, "You joy! let's rock and
make it part of core NOW!" it would have been considered negative by you.

Sincerely,

Joshua D. Drake

--

=== The PostgreSQL Company: Command Prompt, Inc. ===
Sales/Support: +1.503.667.4564 || 24x7/Emergency: +1.800.492.2240
Providing the most comprehensive PostgreSQL solutions since 1997
http://www.commandprompt.com/

Donate to the PostgreSQL Project: http://www.postgresql.org/about/donate
PostgreSQL Replication: http://www.commandprompt.com/products/

getting back on topic (ahem), florian: are you comfortable going ahead
with this? is there anything you need help with?

merlin

Merlin Moncure wrote:
> getting back on topic (ahem), florian: are you comfortable going ahead
> with this? is there anything you need help with?

I'm currently updating my proposal, trying to incorporate the points
people brought up in this thread.

I realized that trying to use the same kind of "read only mode" for
both a standalone postgres (with the datadir on read-only storage),
and a PITR-slave was missguided -
http://archives.postgresql.org/pgsql-hackers/2005-11/msg01043.php
was really enlightning ;-)

Tom's objects regarding performance are the hardest one to deal with -
I'm currently thinking about ways that the locking requirements could
be relaxed - though I still plan to do a basic implementation first, and
then try to improve it.

I'll post an updated proposal during the next few days.

greetings, Florian Pflug

Hello,

I just wanted to voice my opinion for this feature... I've implemented a
few Production applicaitons with PostgreSQL now and would die for that
feature. Right now, I am constantly trying to find way's to make my data
more available. I've even resulted to using pg_dump to create read only
copies of the database and placed them behind load balancers to make the
data more available. Something like this would allow me to quickly leverage
a read only node to scale out the applicaiton... If it can at all be built,
it would get my first, second and third vote. :)

Regards,

Paul Silveira

Jonah H. Harris-2 wrote:
>
> On 2/26/07, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>> Jonah, I have no idea what "fault" you are trying to blame on the
>> community in the above statement. The author didn't discuss the idea
>> with the community before spending months on it so we have no obligation
>> to accept it in the core.
>
> You're missing the point entirely. The majority of the (vocal)
> community didn't even want the feature and as such, failed to provide
> viable suggestions for him to move forward. As the majority of the
> community didn't want the feature, it wouldn't have made a difference
> when he proposed it; which would have remained negative nonetheless.
>
> --
> Jonah H. Harris, Software Architect | phone: 732.331.1324
> EnterpriseDB Corporation | fax: 732.331.1301
> 33 Wood Ave S, 3rd Floor | jharris(at)enterprisedb(dot)com
> Iselin, New Jersey 08830 | http://www.enterprisedb.com/
>
> ---------------------------(end of broadcast)---------------------------
> TIP 7: You can help support the PostgreSQL project by donating at
>
> http://www.postgresql.org/about/donate
>
>

--
View this message in context: http://www.nabble.com/Proposal-for-Implenting-read-only-queries-during-wal-replay-%28SoC-2007%29-tf3279821.html#a9197770
Sent from the PostgreSQL - hackers mailing list archive at Nabble.com.

Paul Silveira wrote:
> Hello,
>
> I just wanted to voice my opinion for this feature... I've implemented a
> few Production applicaitons with PostgreSQL now and would die for that
> feature. Right now, I am constantly trying to find way's to make my data
> more available.

Paul unfortunately you have responded to a hijacked thread. Jonah was
speaking about a project that he wishes would have been accepted which
was called Full Disjunctions.

I have not read the read-only queries during wal replay thread but I can
assure you that Jonah's response had nothing to do with it.

Joshua D. Drake

I've even resulted to using pg_dump to create read only
> copies of the database and placed them behind load balancers to make the
> data more available. Something like this would allow me to quickly leverage
> a read only node to scale out the applicaiton... If it can at all be built,
> it would get my first, second and third vote. :)
>
> Regards,
>
> Paul Silveira
>
>
>
>
> Jonah H. Harris-2 wrote:
>> On 2/26/07, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>>> Jonah, I have no idea what "fault" you are trying to blame on the
>>> community in the above statement. The author didn't discuss the idea
>>> with the community before spending months on it so we have no obligation
>>> to accept it in the core.
>> You're missing the point entirely. The majority of the (vocal)
>> community didn't even want the feature and as such, failed to provide
>> viable suggestions for him to move forward. As the majority of the
>> community didn't want the feature, it wouldn't have made a difference
>> when he proposed it; which would have remained negative nonetheless.
>>
>> --
>> Jonah H. Harris, Software Architect | phone: 732.331.1324
>> EnterpriseDB Corporation | fax: 732.331.1301
>> 33 Wood Ave S, 3rd Floor | jharris(at)enterprisedb(dot)com
>> Iselin, New Jersey 08830 | http://www.enterprisedb.com/
>>
>> ---------------------------(end of broadcast)---------------------------
>> TIP 7: You can help support the PostgreSQL project by donating at
>>
>> http://www.postgresql.org/about/donate
>>
>>
>

--

=== The PostgreSQL Company: Command Prompt, Inc. ===
Sales/Support: +1.503.667.4564 || 24x7/Emergency: +1.800.492.2240
Providing the most comprehensive PostgreSQL solutions since 1997
http://www.commandprompt.com/

Donate to the PostgreSQL Project: http://www.postgresql.org/about/donate
PostgreSQL Replication: http://www.commandprompt.com/products/

Thanks Josh,

I'll look for the earlier one and try to add it there...

-Paul

-----Original Message-----
From: Joshua D. Drake [mailto:jd(at)commandprompt(dot)com]
Sent: Wednesday, February 28, 2007 12:09 AM
To: Paul Silveira
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: [HACKERS] Proposal for Implenting read-only queries during wal
replay (SoC 2007)

Paul Silveira wrote:
> Hello,
>
> I just wanted to voice my opinion for this feature... I've implemented a
> few Production applicaitons with PostgreSQL now and would die for that
> feature. Right now, I am constantly trying to find way's to make my data
> more available.

Paul unfortunately you have responded to a hijacked thread. Jonah was
speaking about a project that he wishes would have been accepted which
was called Full Disjunctions.

I have not read the read-only queries during wal replay thread but I can
assure you that Jonah's response had nothing to do with it.

Joshua D. Drake

I've even resulted to using pg_dump to create read only
> copies of the database and placed them behind load balancers to make the
> data more available. Something like this would allow me to quickly
leverage
> a read only node to scale out the applicaiton... If it can at all be
built,
> it would get my first, second and third vote. :)
>
> Regards,
>
> Paul Silveira
>
>
>
>
> Jonah H. Harris-2 wrote:
>> On 2/26/07, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>>> Jonah, I have no idea what "fault" you are trying to blame on the
>>> community in the above statement. The author didn't discuss the idea
>>> with the community before spending months on it so we have no obligation
>>> to accept it in the core.
>> You're missing the point entirely. The majority of the (vocal)
>> community didn't even want the feature and as such, failed to provide
>> viable suggestions for him to move forward. As the majority of the
>> community didn't want the feature, it wouldn't have made a difference
>> when he proposed it; which would have remained negative nonetheless.
>>
>> --
>> Jonah H. Harris, Software Architect | phone: 732.331.1324
>> EnterpriseDB Corporation | fax: 732.331.1301
>> 33 Wood Ave S, 3rd Floor | jharris(at)enterprisedb(dot)com
>> Iselin, New Jersey 08830 | http://www.enterprisedb.com/
>>
>> ---------------------------(end of broadcast)---------------------------
>> TIP 7: You can help support the PostgreSQL project by donating at
>>
>> http://www.postgresql.org/about/donate
>>
>>
>

--

=== The PostgreSQL Company: Command Prompt, Inc. ===
Sales/Support: +1.503.667.4564 || 24x7/Emergency: +1.800.492.2240
Providing the most comprehensive PostgreSQL solutions since 1997
http://www.commandprompt.com/

Donate to the PostgreSQL Project: http://www.postgresql.org/about/donate
PostgreSQL Replication: http://www.commandprompt.com/products/