Обсуждение: 100% failover + replication solution

> Guys,
>
> I have been thinking about this and wanted to see if it can be
> achived. I wanted to make a 100% failover solution for my postgres
> databases. The first thing that comes to my mind is doing it using
> WAL logs. Am attaching the diagram for which i will write more here.

While its not the solution you were looking at, have you seen
PGCluser :-

http://pgcluster.projects.postgresql.org/index.html

I have not tried it, but was looking the other week at various fail-
over type solutions and came across it. It seems to be able to do
what you want.

Ben






---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not
       match

There is this project which actually is not released yet, but something that you want to achieve :)

http://pgfoundry.org/projects/pgpitrha

Regards,
-------
Shoaib Mir
EnterpriseDB (www.enterprisedb.com)

On 10/30/06, Ben Suffolk < ben@vanilla.net> wrote:

> Guys,
>
> I have been thinking about this and wanted to see if it can be
> achived. I wanted to make a 100% failover solution for my postgres
> databases. The first thing that comes to my mind is doing it using
> WAL logs. Am attaching the diagram for which i will write more here.

While its not the solution you were looking at, have you seen
PGCluser :-

http://pgcluster.projects.postgresql.org/index.html

I have not tried it, but was looking the other week at various fail-
over type solutions and came across it. It seems to be able to do
what you want.

Ben

---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not
       match

Moiz,

it depends on your application (must use JDBC), but you may want to look
at Sequoia, the continuation of the C-JDBC project.

Regards, Oliver.

---------------------------(end of broadcast)---------------------------
TIP 2: Don't 'kill -9' the postmaster

Shoaib,

It sure does, i saw PGCLUSTER, but 3 reasons for having a postgres specific solution.

1) If pgcluster stops further development, it would be lot more hassel when upgrading to a different version of postgres.
2) Postgres specific solution would help alot going ahead in future.
3) Also architecture of pgcluster might make things slower as it updates complete cluster before confirming the request.

There are lots of them available in market, but i think WAL solution should be available, if not then the thought process should be there going ahead. I am expecting a solution out of WAL logs. Let me know if you have any thoughts about it.

Regards,
Moiz Kothari

On 10/30/06, Shoaib Mir < shoaibmir@gmail.com> wrote:

There is this project which actually is not released yet, but something that you want to achieve :)

http://pgfoundry.org/projects/pgpitrha

Regards,
-------
Shoaib Mir
EnterpriseDB (www.enterprisedb.com)

On 10/30/06, Ben Suffolk < ben@vanilla.net> wrote:

> Guys,
>
> I have been thinking about this and wanted to see if it can be
> achived. I wanted to make a 100% failover solution for my postgres
> databases. The first thing that comes to my mind is doing it using
> WAL logs. Am attaching the diagram for which i will write more here.

While its not the solution you were looking at, have you seen
PGCluser :-

http://pgcluster.projects.postgresql.org/index.html

I have not tried it, but was looking the other week at various fail-
over type solutions and came across it. It seems to be able to do
what you want.

Ben

---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not
       match

Hi Moiz,

If I had to choose for your case where you want to direct your selects to slave node and inserts/updates on master, I would have opted for Slony or PGCluster.

Using PITR for HA can be a good option if you want to switch between primary and secondary server, where you can store the archive files on a shared disk and place a recovery file with in $PGDATA and automate the process where it can run the process of recovery on each primary and seconday like for example 5 times a day as it all depends on the number of transactions happening on the db server. I have seen a few users doing this for routine VACUUM FULL process as a maintanence activity.

Thanks,
---------
Shoaib Mir
EnterpriseDB (www.enterprisedb.com)

On 10/30/06, Moiz Kothari < moizpostgres@gmail.com> wrote:

Shoaib,

It sure does, i saw PGCLUSTER, but 3 reasons for having a postgres specific solution.

1) If pgcluster stops further development, it would be lot more hassel when upgrading to a different version of postgres.
2) Postgres specific solution would help alot going ahead in future.
3) Also architecture of pgcluster might make things slower as it updates complete cluster before confirming the request.

There are lots of them available in market, but i think WAL solution should be available, if not then the thought process should be there going ahead. I am expecting a solution out of WAL logs. Let me know if you have any thoughts about it.

Regards,
Moiz Kothari

On 10/30/06, Shoaib Mir < shoaibmir@gmail.com> wrote:

There is this project which actually is not released yet, but something that you want to achieve :)

http://pgfoundry.org/projects/pgpitrha

Regards,
-------
Shoaib Mir
EnterpriseDB (www.enterprisedb.com)

On 10/30/06, Ben Suffolk < ben@vanilla.net> wrote:

> Guys,
>
> I have been thinking about this and wanted to see if it can be
> achived. I wanted to make a 100% failover solution for my postgres
> databases. The first thing that comes to my mind is doing it using
> WAL logs. Am attaching the diagram for which i will write more here.

While its not the solution you were looking at, have you seen
PGCluser :-

http://pgcluster.projects.postgresql.org/index.html

I have not tried it, but was looking the other week at various fail-
over type solutions and came across it. It seems to be able to do
what you want.

Ben

---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not
       match

Shoaib,

I agree that PGCluster might be a better option, i dont want to go with Slony because of primary key constraints. But PGCluster is a good option, the only concerns are :

1) It might slow down the process a bit. as confirmation happens after transaction gets comitted to all the nodes.
2) Its difficult to convince, as it is an external project and if support for the same stops or future versions of postgres does not work, it might be a problem.

Can you elaborate more the way PITR for HA being used for primary and secondary servers, maybe u can light a bulb in me for me to go ahead with the approach. I like the idea of using WAL logs because its postgres internal and secondly it would be fastest way of keeping databases in sync without slowing down other servers.

Awaiting your reply.

Regards,
Moiz Kothari

On 10/30/06, Shoaib Mir < shoaibmir@gmail.com> wrote:

Hi Moiz,

If I had to choose for your case where you want to direct your selects to slave node and inserts/updates on master, I would have opted for Slony or PGCluster.

Using PITR for HA can be a good option if you want to switch between primary and secondary server, where you can store the archive files on a shared disk and place a recovery file with in $PGDATA and automate the process where it can run the process of recovery on each primary and seconday like for example 5 times a day as it all depends on the number of transactions happening on the db server. I have seen a few users doing this for routine VACUUM FULL process as a maintanence activity.

Thanks,
---------
Shoaib Mir
EnterpriseDB (www.enterprisedb.com)

On 10/30/06, Moiz Kothari < moizpostgres@gmail.com> wrote:

Shoaib,

It sure does, i saw PGCLUSTER, but 3 reasons for having a postgres specific solution.

1) If pgcluster stops further development, it would be lot more hassel when upgrading to a different version of postgres.
2) Postgres specific solution would help alot going ahead in future.
3) Also architecture of pgcluster might make things slower as it updates complete cluster before confirming the request.

There are lots of them available in market, but i think WAL solution should be available, if not then the thought process should be there going ahead. I am expecting a solution out of WAL logs. Let me know if you have any thoughts about it.

Regards,
Moiz Kothari

On 10/30/06, Shoaib Mir < shoaibmir@gmail.com> wrote:

There is this project which actually is not released yet, but something that you want to achieve :)

http://pgfoundry.org/projects/pgpitrha

Regards,
-------
Shoaib Mir
EnterpriseDB (www.enterprisedb.com)

On 10/30/06, Ben Suffolk < ben@vanilla.net> wrote:

> Guys,
>
> I have been thinking about this and wanted to see if it can be
> achived. I wanted to make a 100% failover solution for my postgres
> databases. The first thing that comes to my mind is doing it using
> WAL logs. Am attaching the diagram for which i will write more here.

While its not the solution you were looking at, have you seen
PGCluser :-

http://pgcluster.projects.postgresql.org/index.html

I have not tried it, but was looking the other week at various fail-
over type solutions and came across it. It seems to be able to do
what you want.

Ben

---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not
       match

On Mon, Oct 30, 2006 at 06:41:54PM +0530, Moiz Kothari wrote:
> I agree that PGCluster might be a better option, i dont want to go with
> Slony because of primary key constraints.

I don't know what the "primary key constraints" issue you have is,
but Slony would be inappropriate for a "100% failover" system anyway:
you can't know you haven't trapped data on the origin.  This is in
fact true for the WAL shipping you suggested, also.  The only way to
achieve 100% reliable failover today, with guaranteed no data loss,
is to use a system that commits all the data on two machines at the
same time in the same transaction.  I haven't seen any argument so
far that there is any such system "out of the box", although with two
phase commit support available, it would seem that some systems could
be extended in that direction.

The other answer for all of this is to do it with hardware, but
that's a shared-disk system, so if your disk blows up, you have a
problem.  Or, if you're using the operating system of people who
don't know how fsck works.  I don't know anyone who has that problem;
certainly not any vendors whose name starts with 'I' and ends with
'M'.

> 1) It might slow down the process a bit. as confirmation happens after
> transaction gets comitted to all the nodes.

Anyone who tells you that you can have completely reliable data
replication with no performance hit is trying to sell you a bridge in
Brooklyn.  If you want reliable data replication that guarantees you
can have automatic failover, you are going to pay for it somehow; the
question is which compromise you want to make.  That seems to be
something you'll need to decide.

> 2) Its difficult to convince, as it is an external project and if support
> for the same stops or future versions of postgres does not work, it might be
> a problem.

If you have this problem, probably free software isn't for you.
PostgreSQL is a modular system, and people use different components
together in deployed systems.  This happens to be true of commercial
offerings too (if not, you could buy the cheapest version of, say,
Oracle and get RAC in the bargain), but they _sell_ it to you as
though it were one big package.  To the extent your managers don't
understand this, you're always going to have a problem using free
software.

A
--
Andrew Sullivan  | ajs@crankycanuck.ca
In the future this spectacle of the middle classes shocking the avant-
garde will probably become the textbook definition of Postmodernism.
                --Brad Holland

---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not
       match

Hi Moiz,

This might help you :) --> http://developer.postgresql.org/pgdocs/postgres/warm-standby.html

Thanks,
-------
Shoaib Mir
EnterpriseDB (www.enterprisedb.com)

On 10/30/06, Andrew Sullivan < ajs@crankycanuck.ca> wrote:

On Mon, Oct 30, 2006 at 06:41:54PM +0530, Moiz Kothari wrote:
> I agree that PGCluster might be a better option, i dont want to go with
> Slony because of primary key constraints.

I don't know what the "primary key constraints" issue you have is,
but Slony would be inappropriate for a "100% failover" system anyway:
you can't know you haven't trapped data on the origin.  This is in
fact true for the WAL shipping you suggested, also.  The only way to
achieve 100% reliable failover today, with guaranteed no data loss,
is to use a system that commits all the data on two machines at the
same time in the same transaction.  I haven't seen any argument so
far that there is any such system "out of the box", although with two
phase commit support available, it would seem that some systems could
be extended in that direction.

The other answer for all of this is to do it with hardware, but
that's a shared-disk system, so if your disk blows up, you have a
problem.  Or, if you're using the operating system of people who
don't know how fsck works.  I don't know anyone who has that problem;
certainly not any vendors whose name starts with 'I' and ends with
'M'.

> 1) It might slow down the process a bit. as confirmation happens after
> transaction gets comitted to all the nodes.

Anyone who tells you that you can have completely reliable data
replication with no performance hit is trying to sell you a bridge in
Brooklyn.  If you want reliable data replication that guarantees you
can have automatic failover, you are going to pay for it somehow; the
question is which compromise you want to make.  That seems to be
something you'll need to decide.

> 2) Its difficult to convince, as it is an external project and if support
> for the same stops or future versions of postgres does not work, it might be
> a problem.

If you have this problem, probably free software isn't for you.
PostgreSQL is a modular system, and people use different components
together in deployed systems.  This happens to be true of commercial
offerings too (if not, you could buy the cheapest version of, say,
Oracle and get RAC in the bargain), but they _sell_ it to you as
though it were one big package.  To the extent your managers don't
understand this, you're always going to have a problem using free
software.

A
--
Andrew Sullivan  | ajs@crankycanuck.ca
In the future this spectacle of the middle classes shocking the avant-
garde will probably become the textbook definition of Postmodernism.
                --Brad Holland

---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not
       match

Shoaib,

This sounds really like what i need, but again 8.2 is in beta.

Just one question, i dunno if i am thinking in right direction, but is there anyway of finding out the END XID, transaction id and OID of last archived WAL log applied to the database. I was thinking if i can get that value then i can reset XLOGs using pg_resetxlog to that point and then start applying the new WAL logs. Am i thinking it correctly or there is some flaw here.

Also if i am thinking it right, then how can i find the details i asked above.

Regards,
Moiz Kothari

On 10/30/06, Shoaib Mir < shoaibmir@gmail.com> wrote:

Hi Moiz,

This might help you :) --> http://developer.postgresql.org/pgdocs/postgres/warm-standby.html

Thanks,
-------
Shoaib Mir
EnterpriseDB (www.enterprisedb.com)

On 10/30/06, Andrew Sullivan < ajs@crankycanuck.ca> wrote:

On Mon, Oct 30, 2006 at 06:41:54PM +0530, Moiz Kothari wrote:
> I agree that PGCluster might be a better option, i dont want to go with
> Slony because of primary key constraints.

I don't know what the "primary key constraints" issue you have is,
but Slony would be inappropriate for a "100% failover" system anyway:
you can't know you haven't trapped data on the origin.  This is in
fact true for the WAL shipping you suggested, also.  The only way to
achieve 100% reliable failover today, with guaranteed no data loss,
is to use a system that commits all the data on two machines at the
same time in the same transaction.  I haven't seen any argument so
far that there is any such system "out of the box", although with two
phase commit support available, it would seem that some systems could
be extended in that direction.

The other answer for all of this is to do it with hardware, but
that's a shared-disk system, so if your disk blows up, you have a
problem.  Or, if you're using the operating system of people who
don't know how fsck works.  I don't know anyone who has that problem;
certainly not any vendors whose name starts with 'I' and ends with
'M'.

> 1) It might slow down the process a bit. as confirmation happens after
> transaction gets comitted to all the nodes.

Anyone who tells you that you can have completely reliable data
replication with no performance hit is trying to sell you a bridge in
Brooklyn.  If you want reliable data replication that guarantees you
can have automatic failover, you are going to pay for it somehow; the
question is which compromise you want to make.  That seems to be
something you'll need to decide.

> 2) Its difficult to convince, as it is an external project and if support
> for the same stops or future versions of postgres does not work, it might be
> a problem.

If you have this problem, probably free software isn't for you.
PostgreSQL is a modular system, and people use different components
together in deployed systems.  This happens to be true of commercial
offerings too (if not, you could buy the cheapest version of, say,
Oracle and get RAC in the bargain), but they _sell_ it to you as
though it were one big package.  To the extent your managers don't
understand this, you're always going to have a problem using free
software.

A
--
Andrew Sullivan  | ajs@crankycanuck.ca
In the future this spectacle of the middle classes shocking the avant-
garde will probably become the textbook definition of Postmodernism.
                --Brad Holland

---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not
       match

Moiz,

Hmmmm, I think pg_controldata output might help you there to get these stats.

pg_controldata can be found in the PostgreSQL /bin folder.

Thank you,
---------
Shoaib Mir
EnterpriseDB ( www.enterprisedb.com)

On 10/31/06, Moiz Kothari < moizpostgres@gmail.com> wrote:

Shoaib,

This sounds really like what i need, but again 8.2 is in beta.

Just one question, i dunno if i am thinking in right direction, but is there anyway of finding out the END XID, transaction id and OID of last archived WAL log applied to the database. I was thinking if i can get that value then i can reset XLOGs using pg_resetxlog to that point and then start applying the new WAL logs. Am i thinking it correctly or there is some flaw here.

Also if i am thinking it right, then how can i find the details i asked above.

Regards,
Moiz Kothari

On 10/30/06, Shoaib Mir < shoaibmir@gmail.com> wrote:

Hi Moiz,

This might help you :) --> http://developer.postgresql.org/pgdocs/postgres/warm-standby.html

Thanks,
-------
Shoaib Mir
EnterpriseDB (www.enterprisedb.com)

On 10/30/06, Andrew Sullivan < ajs@crankycanuck.ca> wrote:

On Mon, Oct 30, 2006 at 06:41:54PM +0530, Moiz Kothari wrote:
> I agree that PGCluster might be a better option, i dont want to go with
> Slony because of primary key constraints.

I don't know what the "primary key constraints" issue you have is,
but Slony would be inappropriate for a "100% failover" system anyway:
you can't know you haven't trapped data on the origin.  This is in
fact true for the WAL shipping you suggested, also.  The only way to
achieve 100% reliable failover today, with guaranteed no data loss,
is to use a system that commits all the data on two machines at the
same time in the same transaction.  I haven't seen any argument so
far that there is any such system "out of the box", although with two
phase commit support available, it would seem that some systems could
be extended in that direction.

The other answer for all of this is to do it with hardware, but
that's a shared-disk system, so if your disk blows up, you have a
problem.  Or, if you're using the operating system of people who
don't know how fsck works.  I don't know anyone who has that problem;
certainly not any vendors whose name starts with 'I' and ends with
'M'.

> 1) It might slow down the process a bit. as confirmation happens after
> transaction gets comitted to all the nodes.

Anyone who tells you that you can have completely reliable data
replication with no performance hit is trying to sell you a bridge in
Brooklyn.  If you want reliable data replication that guarantees you
can have automatic failover, you are going to pay for it somehow; the
question is which compromise you want to make.  That seems to be
something you'll need to decide.

> 2) Its difficult to convince, as it is an external project and if support
> for the same stops or future versions of postgres does not work, it might be
> a problem.

If you have this problem, probably free software isn't for you.
PostgreSQL is a modular system, and people use different components
together in deployed systems.  This happens to be true of commercial
offerings too (if not, you could buy the cheapest version of, say,
Oracle and get RAC in the bargain), but they _sell_ it to you as
though it were one big package.  To the extent your managers don't
understand this, you're always going to have a problem using free
software.

A
--
Andrew Sullivan  | ajs@crankycanuck.ca
In the future this spectacle of the middle classes shocking the avant-
garde will probably become the textbook definition of Postmodernism.
                --Brad Holland

---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not
       match

Shoaib,

Also just so you know, we plan to use SLES 10 OS. so also let me know the compatibility of EnterpriseDB to the OS.

Regards,
Moiz

On 10/31/06, Shoaib Mir <shoaibmir@gmail.com> wrote:

Moiz,

Hmmmm, I think pg_controldata output might help you there to get these stats.

pg_controldata can be found in the PostgreSQL /bin folder.

Thank you,
---------
Shoaib Mir
EnterpriseDB ( www.enterprisedb.com)

On 10/31/06, Moiz Kothari < moizpostgres@gmail.com> wrote:

Shoaib,

This sounds really like what i need, but again 8.2 is in beta.

Just one question, i dunno if i am thinking in right direction, but is there anyway of finding out the END XID, transaction id and OID of last archived WAL log applied to the database. I was thinking if i can get that value then i can reset XLOGs using pg_resetxlog to that point and then start applying the new WAL logs. Am i thinking it correctly or there is some flaw here.

Also if i am thinking it right, then how can i find the details i asked above.

Regards,
Moiz Kothari

On 10/30/06, Shoaib Mir < shoaibmir@gmail.com> wrote:

Hi Moiz,

This might help you :) --> http://developer.postgresql.org/pgdocs/postgres/warm-standby.html

Thanks,
-------
Shoaib Mir
EnterpriseDB (www.enterprisedb.com)

On 10/30/06, Andrew Sullivan < ajs@crankycanuck.ca> wrote:

On Mon, Oct 30, 2006 at 06:41:54PM +0530, Moiz Kothari wrote:
> I agree that PGCluster might be a better option, i dont want to go with
> Slony because of primary key constraints.

I don't know what the "primary key constraints" issue you have is,
but Slony would be inappropriate for a "100% failover" system anyway:
you can't know you haven't trapped data on the origin.  This is in
fact true for the WAL shipping you suggested, also.  The only way to
achieve 100% reliable failover today, with guaranteed no data loss,
is to use a system that commits all the data on two machines at the
same time in the same transaction.  I haven't seen any argument so
far that there is any such system "out of the box", although with two
phase commit support available, it would seem that some systems could
be extended in that direction.

The other answer for all of this is to do it with hardware, but
that's a shared-disk system, so if your disk blows up, you have a
problem.  Or, if you're using the operating system of people who
don't know how fsck works.  I don't know anyone who has that problem;
certainly not any vendors whose name starts with 'I' and ends with
'M'.

> 1) It might slow down the process a bit. as confirmation happens after
> transaction gets comitted to all the nodes.

Anyone who tells you that you can have completely reliable data
replication with no performance hit is trying to sell you a bridge in
Brooklyn.  If you want reliable data replication that guarantees you
can have automatic failover, you are going to pay for it somehow; the
question is which compromise you want to make.  That seems to be
something you'll need to decide.

> 2) Its difficult to convince, as it is an external project and if support
> for the same stops or future versions of postgres does not work, it might be
> a problem.

If you have this problem, probably free software isn't for you.
PostgreSQL is a modular system, and people use different components
together in deployed systems.  This happens to be true of commercial
offerings too (if not, you could buy the cheapest version of, say,
Oracle and get RAC in the bargain), but they _sell_ it to you as
though it were one big package.  To the extent your managers don't
understand this, you're always going to have a problem using free
software.

A
--
Andrew Sullivan  | ajs@crankycanuck.ca
In the future this spectacle of the middle classes shocking the avant-
garde will probably become the textbook definition of Postmodernism.
                --Brad Holland

---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not
       match

Moiz,

Hmmmm, I think pg_controldata output might help you there to get these stats.

pg_controldata can be found in the PostgreSQL /bin folder.

Thank you,
---------
Shoaib Mir
EnterpriseDB ( www.enterprisedb.com)

On 10/31/06, Moiz Kothari < moizpostgres@gmail.com> wrote:

Shoaib,

This sounds really like what i need, but again 8.2 is in beta.

Just one question, i dunno if i am thinking in right direction, but is there anyway of finding out the END XID, transaction id and OID of last archived WAL log applied to the database. I was thinking if i can get that value then i can reset XLOGs using pg_resetxlog to that point and then start applying the new WAL logs. Am i thinking it correctly or there is some flaw here.

Also if i am thinking it right, then how can i find the details i asked above.

Regards,
Moiz Kothari

On 10/30/06, Shoaib Mir < shoaibmir@gmail.com> wrote:

Hi Moiz,

This might help you :) --> http://developer.postgresql.org/pgdocs/postgres/warm-standby.html

Thanks,
-------
Shoaib Mir
EnterpriseDB (www.enterprisedb.com)

On 10/30/06, Andrew Sullivan < ajs@crankycanuck.ca> wrote:

On Mon, Oct 30, 2006 at 06:41:54PM +0530, Moiz Kothari wrote:
> I agree that PGCluster might be a better option, i dont want to go with
> Slony because of primary key constraints.

I don't know what the "primary key constraints" issue you have is,
but Slony would be inappropriate for a "100% failover" system anyway:
you can't know you haven't trapped data on the origin.  This is in
fact true for the WAL shipping you suggested, also.  The only way to
achieve 100% reliable failover today, with guaranteed no data loss,
is to use a system that commits all the data on two machines at the
same time in the same transaction.  I haven't seen any argument so
far that there is any such system "out of the box", although with two
phase commit support available, it would seem that some systems could
be extended in that direction.

The other answer for all of this is to do it with hardware, but
that's a shared-disk system, so if your disk blows up, you have a
problem.  Or, if you're using the operating system of people who
don't know how fsck works.  I don't know anyone who has that problem;
certainly not any vendors whose name starts with 'I' and ends with
'M'.

> 1) It might slow down the process a bit. as confirmation happens after
> transaction gets comitted to all the nodes.

Anyone who tells you that you can have completely reliable data
replication with no performance hit is trying to sell you a bridge in
Brooklyn.  If you want reliable data replication that guarantees you
can have automatic failover, you are going to pay for it somehow; the
question is which compromise you want to make.  That seems to be
something you'll need to decide.

> 2) Its difficult to convince, as it is an external project and if support
> for the same stops or future versions of postgres does not work, it might be
> a problem.

If you have this problem, probably free software isn't for you.
PostgreSQL is a modular system, and people use different components
together in deployed systems.  This happens to be true of commercial
offerings too (if not, you could buy the cheapest version of, say,
Oracle and get RAC in the bargain), but they _sell_ it to you as
though it were one big package.  To the extent your managers don't
understand this, you're always going to have a problem using free
software.

A
--
Andrew Sullivan  | ajs@crankycanuck.ca
In the future this spectacle of the middle classes shocking the avant-
garde will probably become the textbook definition of Postmodernism.
                --Brad Holland

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TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not
       match