Обсуждение: Clustering & Load Balancing & Replication

Thanks Chris,
I see you a core member of Slony team and a replication guru so I'll look
into it.
I'm not slamming Slony I think its probably the right tool for type of work
your company Afilias does. Just wish you would make an official Windows
version of Slony as well.
Anyway thanks for the education, and I think it would be a good thing if
your site on replication, was also listed on Postgresql... good research.
Merry Xmas

----- Original Message -----
From: "Christopher Browne" <cbbrowne@acm.org>
To: <pgsql-general@postgresql.org>
Sent: Sunday, December 24, 2006 4:23 AM
Subject: Re: [GENERAL] Clustering & Load Balancing & Replication


> Centuries ago, Nostradamus foresaw when org@kewlstuff.co.za would write:
>> Suggest you download my little application and read the documentation,
>> you'll see its very different, maybe even interesting.
>> Maybe they should change that to.... Postgres DOES HAVE a free
>> multi-master
>> replication system :)
>
> It isn't systematically usable as such, without a whole lot of
> end-user assembly.
>
>> One comment they make.... "Heavy write activity can cause excessive
>> locking,
>> leading to poor performance. In fact, write performance is often worse
>> than
>> that of a single server. Read requests can be sent to any server."
>> I'm not sure I agree with that... or maybe MVCC is just fantastic.... I
>> tested it.
>> The 2 phase commit locking is definitely happening at record level, so
>> only
>> if the multimasters all hit the same record is there the potential for
>> lock
>> conflict.
>> Why will dB's being randomly used, hit the same records, I think its a
>> low
>> probability to begin with?
>
> That's only true if you are certain that the update pattern is NOT
> involving a shared set of records.  IN GENERAL, heavy write activity
> can cause locking to become mighty expensive, which is certainly a
> true statement.
>
>> Not happy with that, I wrote a multithreaded routine and got them to all
>> smack the same record, it NEVER ROLLED BACK, and if there is performance
>> degradation, I didnt notice it... again probably a testament to the MVCC
>> design.
>
> It seems likely to me that this requires some careful validation of
> testing.
>
> An effect we see is that if a set of transactions are "fighting" over
> a single "balance" record, they will essentially serialize over that.
>
> On a system with a single CPU, it is not obvious that you'll see a
> degradation there because, since you only have the single CPU, it
> would be serializing the activity anyways.
>
> Try it out on an 8-way SMP system and you may see things differently.
>
>> In any event if you look at the documentation, you'll see SPAR is not
>> multimaster or nothing. Can use say one server in an office and another
>> to
>> pump data to a remote web site... not sure if you would even call that
>> multimaster, thats the point, I'm not sure SPAR fits any pure theory
>> category.
>
> There are a few tests I could throw at it that tend to challenge
> replication systems vis-a-vis "fidelity of results."  I otta see if I
> can find them in a readily deployable form.
>
> There are two notable anomalies which have been known to break
> replication systems:
>
> 1.  Nondeterministic updates:
>
> For instance, functions that are nondeterministic:
>
>  insert into rtable values (random(), now());
>
> Or result sets that are nondeterministic:
>
>  insert into rtable2 (select * from mytable where some_attr='foo'
>     order by random() limit 5);   -- Where there are 25 records with
> some_attr='foo'
>
> 2.  Value swapping:
>
> Consider the table:
>
> create table t1 (mk integer primary key, val text unique not null);
>
> insert into t1 (mk, val) values (1, 'chris');
> insert into t1 (mk, val) values (2, 'dave');
> insert into t1 (mk, val) values (3, 'brad');
>
> begin;
> update t1 set mk = 99 where mk = 1;
> update t1 set mk = 1 where mk = 3;
> update t1 set mk = 3 where mk = 99;
> commit;
>
> Is there a condition where a pause somewhere in there will cause
> replication to break?  Note that there have been replication systems
> (erServer) that this set of updates can, intermittently, cause to fall
> over.
> --
> let name="cbbrowne" and tld="linuxfinances.info" in String.concat "@"
> [name;tld];;
> http://cbbrowne.com/info/slony.html
> "Feel free to  contact me (flames about my english  and the useless of
> this driver will be redirected to /dev/null, oh no, it's full...)"
> -- Michael Beck, describing the PC-speaker sound device
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: Don't 'kill -9' the postmaster
>


---------------------------(end of broadcast)---------------------------
TIP 5: don't forget to increase your free space map settings

I guess the latest 8.2 Windows PostgreSQL installer does come with a Slony option and you can set it up easily using pgadmin too.

This link --> http://people.planetpostgresql.org/xzilla/index.php?/archives/200-Alpha-testing-Slony-on-win32-Crib-Notes.html might help you as well.

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

On 12/25/06, org@kewlstuff.co.za <org@kewlstuff.co.za> wrote:

Thanks Chris,
I see you a core member of Slony team and a replication guru so I'll look
into it.
I'm not slamming Slony I think its probably the right tool for type of work
your company Afilias does. Just wish you would make an official Windows
version of Slony as well.
Anyway thanks for the education, and I think it would be a good thing if
your site on replication, was also listed on Postgresql... good research.
Merry Xmas

----- Original Message -----
From: "Christopher Browne" <cbbrowne@acm.org>
To: < pgsql-general@postgresql.org>
Sent: Sunday, December 24, 2006 4:23 AM
Subject: Re: [GENERAL] Clustering & Load Balancing & Replication


> Centuries ago, Nostradamus foresaw when org@kewlstuff.co.za would write:
>> Suggest you download my little application and read the documentation,
>> you'll see its very different, maybe even interesting.
>> Maybe they should change that to.... Postgres DOES HAVE a free
>> multi-master
>> replication system :)
>
> It isn't systematically usable as such, without a whole lot of
> end-user assembly.
>
>> One comment they make.... "Heavy write activity can cause excessive
>> locking,
>> leading to poor performance. In fact, write performance is often worse
>> than
>> that of a single server. Read requests can be sent to any server."
>> I'm not sure I agree with that... or maybe MVCC is just fantastic.... I
>> tested it.
>> The 2 phase commit locking is definitely happening at record level, so
>> only
>> if the multimasters all hit the same record is there the potential for
>> lock
>> conflict.
>> Why will dB's being randomly used, hit the same records, I think its a
>> low
>> probability to begin with?
>
> That's only true if you are certain that the update pattern is NOT
> involving a shared set of records.  IN GENERAL, heavy write activity
> can cause locking to become mighty expensive, which is certainly a
> true statement.
>
>> Not happy with that, I wrote a multithreaded routine and got them to all
>> smack the same record, it NEVER ROLLED BACK, and if there is performance
>> degradation, I didnt notice it... again probably a testament to the MVCC
>> design.
>
> It seems likely to me that this requires some careful validation of
> testing.
>
> An effect we see is that if a set of transactions are "fighting" over
> a single "balance" record, they will essentially serialize over that.
>
> On a system with a single CPU, it is not obvious that you'll see a
> degradation there because, since you only have the single CPU, it
> would be serializing the activity anyways.
>
> Try it out on an 8-way SMP system and you may see things differently.
>
>> In any event if you look at the documentation, you'll see SPAR is not
>> multimaster or nothing. Can use say one server in an office and another
>> to
>> pump data to a remote web site... not sure if you would even call that
>> multimaster, thats the point, I'm not sure SPAR fits any pure theory
>> category.
>
> There are a few tests I could throw at it that tend to challenge
> replication systems vis-a-vis "fidelity of results."  I otta see if I
> can find them in a readily deployable form.
>
> There are two notable anomalies which have been known to break
> replication systems:
>
> 1.  Nondeterministic updates:
>
> For instance, functions that are nondeterministic:
>
>  insert into rtable values (random(), now());
>
> Or result sets that are nondeterministic:
>
>  insert into rtable2 (select * from mytable where some_attr='foo'
>     order by random() limit 5);   -- Where there are 25 records with
> some_attr='foo'
>
> 2.  Value swapping:
>
> Consider the table:
>
> create table t1 (mk integer primary key, val text unique not null);
>
> insert into t1 (mk, val) values (1, 'chris');
> insert into t1 (mk, val) values (2, 'dave');
> insert into t1 (mk, val) values (3, 'brad');
>
> begin;
> update t1 set mk = 99 where mk = 1;
> update t1 set mk = 1 where mk = 3;
> update t1 set mk = 3 where mk = 99;
> commit;
>
> Is there a condition where a pause somewhere in there will cause
> replication to break?  Note that there have been replication systems
> (erServer) that this set of updates can, intermittently, cause to fall
> over.
> --
> let name="cbbrowne" and tld=" linuxfinances.info" in String.concat "@"
> [name;tld];;
> http://cbbrowne.com/info/slony.html
> "Feel free to  contact me (flames about my english  and the useless of
> this driver will be redirected to /dev/null, oh no, it's full...)"
> -- Michael Beck, describing the PC-speaker sound device
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: Don't 'kill -9' the postmaster
>


---------------------------(end of broadcast)---------------------------
TIP 5: don't forget to increase your free space map settings

Hi,

I have just read the statement that Postgres does have (with end user assembly) multi-master replication system.  Is this just PGCluster or something else ? if it is not PGCluster, then how can this be achieved ?

Cheers,

Andy

On 24/12/06, Shoaib Mir < shoaibmir@gmail.com> wrote:

I guess the latest 8.2 Windows PostgreSQL installer does come with a Slony option and you can set it up easily using pgadmin too.

This link --> http://people.planetpostgresql.org/xzilla/index.php?/archives/200-Alpha-testing-Slony-on-win32-Crib-Notes.html might help you as well.

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

On 12/25/06, org@kewlstuff.co.za <org@kewlstuff.co.za> wrote:

Thanks Chris,
I see you a core member of Slony team and a replication guru so I'll look
into it.
I'm not slamming Slony I think its probably the right tool for type of work
your company Afilias does. Just wish you would make an official Windows
version of Slony as well.
Anyway thanks for the education, and I think it would be a good thing if
your site on replication, was also listed on Postgresql... good research.
Merry Xmas

----- Original Message -----
From: "Christopher Browne" <cbbrowne@acm.org>
To: < pgsql-general@postgresql.org>
Sent: Sunday, December 24, 2006 4:23 AM
Subject: Re: [GENERAL] Clustering & Load Balancing & Replication


> Centuries ago, Nostradamus foresaw when org@kewlstuff.co.za would write:
>> Suggest you download my little application and read the documentation,
>> you'll see its very different, maybe even interesting.
>> Maybe they should change that to.... Postgres DOES HAVE a free
>> multi-master
>> replication system :)
>
> It isn't systematically usable as such, without a whole lot of
> end-user assembly.
>
>> One comment they make.... "Heavy write activity can cause excessive
>> locking,
>> leading to poor performance. In fact, write performance is often worse
>> than
>> that of a single server. Read requests can be sent to any server."
>> I'm not sure I agree with that... or maybe MVCC is just fantastic.... I
>> tested it.
>> The 2 phase commit locking is definitely happening at record level, so
>> only
>> if the multimasters all hit the same record is there the potential for
>> lock
>> conflict.
>> Why will dB's being randomly used, hit the same records, I think its a
>> low
>> probability to begin with?
>
> That's only true if you are certain that the update pattern is NOT
> involving a shared set of records.  IN GENERAL, heavy write activity
> can cause locking to become mighty expensive, which is certainly a
> true statement.
>
>> Not happy with that, I wrote a multithreaded routine and got them to all
>> smack the same record, it NEVER ROLLED BACK, and if there is performance
>> degradation, I didnt notice it... again probably a testament to the MVCC
>> design.
>
> It seems likely to me that this requires some careful validation of
> testing.
>
> An effect we see is that if a set of transactions are "fighting" over
> a single "balance" record, they will essentially serialize over that.
>
> On a system with a single CPU, it is not obvious that you'll see a
> degradation there because, since you only have the single CPU, it
> would be serializing the activity anyways.
>
> Try it out on an 8-way SMP system and you may see things differently.
>
>> In any event if you look at the documentation, you'll see SPAR is not
>> multimaster or nothing. Can use say one server in an office and another
>> to
>> pump data to a remote web site... not sure if you would even call that
>> multimaster, thats the point, I'm not sure SPAR fits any pure theory
>> category.
>
> There are a few tests I could throw at it that tend to challenge
> replication systems vis-a-vis "fidelity of results."  I otta see if I
> can find them in a readily deployable form.
>
> There are two notable anomalies which have been known to break
> replication systems:
>
> 1.  Nondeterministic updates:
>
> For instance, functions that are nondeterministic:
>
>  insert into rtable values (random(), now());
>
> Or result sets that are nondeterministic:
>
>  insert into rtable2 (select * from mytable where some_attr='foo'
>     order by random() limit 5);   -- Where there are 25 records with
> some_attr='foo'
>
> 2.  Value swapping:
>
> Consider the table:
>
> create table t1 (mk integer primary key, val text unique not null);
>
> insert into t1 (mk, val) values (1, 'chris');
> insert into t1 (mk, val) values (2, 'dave');
> insert into t1 (mk, val) values (3, 'brad');
>
> begin;
> update t1 set mk = 99 where mk = 1;
> update t1 set mk = 1 where mk = 3;
> update t1 set mk = 3 where mk = 99;
> commit;
>
> Is there a condition where a pause somewhere in there will cause
> replication to break?  Note that there have been replication systems
> (erServer) that this set of updates can, intermittently, cause to fall
> over.
> --
> let name="cbbrowne" and tld=" linuxfinances.info" in String.concat "@"
> [name;tld];;
> http://cbbrowne.com/info/slony.html
> "Feel free to  contact me (flames about my english  and the useless of
> this driver will be redirected to /dev/null, oh no, it's full...)"
> -- Michael Beck, describing the PC-speaker sound device
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: Don't 'kill -9' the postmaster
>


---------------------------(end of broadcast)---------------------------
TIP 5: don't forget to increase your free space map settings

pgpool-II might help you there too I guess...

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

On 12/26/06, Andy Dale <andy.dale@gmail.com> wrote:

Hi,

I have just read the statement that Postgres does have (with end user assembly) multi-master replication system.  Is this just PGCluster or something else ? if it is not PGCluster, then how can this be achieved ?

Cheers,

Andy

On 24/12/06, Shoaib Mir < shoaibmir@gmail.com> wrote:

I guess the latest 8.2 Windows PostgreSQL installer does come with a Slony option and you can set it up easily using pgadmin too.

This link --> http://people.planetpostgresql.org/xzilla/index.php?/archives/200-Alpha-testing-Slony-on-win32-Crib-Notes.html might help you as well.

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

On 12/25/06, org@kewlstuff.co.za <org@kewlstuff.co.za> wrote:

Thanks Chris,
I see you a core member of Slony team and a replication guru so I'll look
into it.
I'm not slamming Slony I think its probably the right tool for type of work
your company Afilias does. Just wish you would make an official Windows
version of Slony as well.
Anyway thanks for the education, and I think it would be a good thing if
your site on replication, was also listed on Postgresql... good research.
Merry Xmas

----- Original Message -----
From: "Christopher Browne" <cbbrowne@acm.org>
To: < pgsql-general@postgresql.org>
Sent: Sunday, December 24, 2006 4:23 AM
Subject: Re: [GENERAL] Clustering & Load Balancing & Replication


> Centuries ago, Nostradamus foresaw when org@kewlstuff.co.za would write:
>> Suggest you download my little application and read the documentation,
>> you'll see its very different, maybe even interesting.
>> Maybe they should change that to.... Postgres DOES HAVE a free
>> multi-master
>> replication system :)
>
> It isn't systematically usable as such, without a whole lot of
> end-user assembly.
>
>> One comment they make.... "Heavy write activity can cause excessive
>> locking,
>> leading to poor performance. In fact, write performance is often worse
>> than
>> that of a single server. Read requests can be sent to any server."
>> I'm not sure I agree with that... or maybe MVCC is just fantastic.... I
>> tested it.
>> The 2 phase commit locking is definitely happening at record level, so
>> only
>> if the multimasters all hit the same record is there the potential for
>> lock
>> conflict.
>> Why will dB's being randomly used, hit the same records, I think its a
>> low
>> probability to begin with?
>
> That's only true if you are certain that the update pattern is NOT
> involving a shared set of records.  IN GENERAL, heavy write activity
> can cause locking to become mighty expensive, which is certainly a
> true statement.
>
>> Not happy with that, I wrote a multithreaded routine and got them to all
>> smack the same record, it NEVER ROLLED BACK, and if there is performance
>> degradation, I didnt notice it... again probably a testament to the MVCC
>> design.
>
> It seems likely to me that this requires some careful validation of
> testing.
>
> An effect we see is that if a set of transactions are "fighting" over
> a single "balance" record, they will essentially serialize over that.
>
> On a system with a single CPU, it is not obvious that you'll see a
> degradation there because, since you only have the single CPU, it
> would be serializing the activity anyways.
>
> Try it out on an 8-way SMP system and you may see things differently.
>
>> In any event if you look at the documentation, you'll see SPAR is not
>> multimaster or nothing. Can use say one server in an office and another
>> to
>> pump data to a remote web site... not sure if you would even call that
>> multimaster, thats the point, I'm not sure SPAR fits any pure theory
>> category.
>
> There are a few tests I could throw at it that tend to challenge
> replication systems vis-a-vis "fidelity of results."  I otta see if I
> can find them in a readily deployable form.
>
> There are two notable anomalies which have been known to break
> replication systems:
>
> 1.  Nondeterministic updates:
>
> For instance, functions that are nondeterministic:
>
>  insert into rtable values (random(), now());
>
> Or result sets that are nondeterministic:
>
>  insert into rtable2 (select * from mytable where some_attr='foo'
>     order by random() limit 5);   -- Where there are 25 records with
> some_attr='foo'
>
> 2.  Value swapping:
>
> Consider the table:
>
> create table t1 (mk integer primary key, val text unique not null);
>
> insert into t1 (mk, val) values (1, 'chris');
> insert into t1 (mk, val) values (2, 'dave');
> insert into t1 (mk, val) values (3, 'brad');
>
> begin;
> update t1 set mk = 99 where mk = 1;
> update t1 set mk = 1 where mk = 3;
> update t1 set mk = 3 where mk = 99;
> commit;
>
> Is there a condition where a pause somewhere in there will cause
> replication to break?  Note that there have been replication systems
> (erServer) that this set of updates can, intermittently, cause to fall
> over.
> --
> let name="cbbrowne" and tld=" linuxfinances.info" in String.concat "@"
> [name;tld];;
> http://cbbrowne.com/info/slony.html
> "Feel free to  contact me (flames about my english  and the useless of
> this driver will be redirected to /dev/null, oh no, it's full...)"
> -- Michael Beck, describing the PC-speaker sound device
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: Don't 'kill -9' the postmaster
>


---------------------------(end of broadcast)---------------------------
TIP 5: don't forget to increase your free space map settings

The issue i had with pgpool (1 or 2) was that (correct me if i am wrong) you had to start the pgpool cluster with both nodes in the same state.  I thought this would mean that if you had a DB fail, before you could re-introduce it into the pgpool cluster you would have to manually sync it with the cluster state, is this correct ??

The system i need multi master sync for is highly transactional, so if the behaviour i stated above is correct it is not suitable.  I have tried s-lony, and while i was pleased with the performance, it is only Single Master - Multi Slave which is not acceptable as well.

Andy

On 26/12/06, Shoaib Mir <shoaibmir@gmail.com > wrote:

pgpool-II might help you there too I guess...

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

On 12/26/06, Andy Dale <andy.dale@gmail.com> wrote:

Hi,

I have just read the statement that Postgres does have (with end user assembly) multi-master replication system.  Is this just PGCluster or something else ? if it is not PGCluster, then how can this be achieved ?

Cheers,

Andy

On 24/12/06, Shoaib Mir < shoaibmir@gmail.com> wrote:

I guess the latest 8.2 Windows PostgreSQL installer does come with a Slony option and you can set it up easily using pgadmin too.

This link --> http://people.planetpostgresql.org/xzilla/index.php?/archives/200-Alpha-testing-Slony-on-win32-Crib-Notes.html might help you as well.

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

On 12/25/06, org@kewlstuff.co.za <org@kewlstuff.co.za> wrote:

Thanks Chris,
I see you a core member of Slony team and a replication guru so I'll look
into it.
I'm not slamming Slony I think its probably the right tool for type of work
your company Afilias does. Just wish you would make an official Windows
version of Slony as well.
Anyway thanks for the education, and I think it would be a good thing if
your site on replication, was also listed on Postgresql... good research.
Merry Xmas

----- Original Message -----
From: "Christopher Browne" <cbbrowne@acm.org>
To: < pgsql-general@postgresql.org>
Sent: Sunday, December 24, 2006 4:23 AM
Subject: Re: [GENERAL] Clustering & Load Balancing & Replication


> Centuries ago, Nostradamus foresaw when org@kewlstuff.co.za would write:
>> Suggest you download my little application and read the documentation,
>> you'll see its very different, maybe even interesting.
>> Maybe they should change that to.... Postgres DOES HAVE a free
>> multi-master
>> replication system :)
>
> It isn't systematically usable as such, without a whole lot of
> end-user assembly.
>
>> One comment they make.... "Heavy write activity can cause excessive
>> locking,
>> leading to poor performance. In fact, write performance is often worse
>> than
>> that of a single server. Read requests can be sent to any server."
>> I'm not sure I agree with that... or maybe MVCC is just fantastic.... I
>> tested it.
>> The 2 phase commit locking is definitely happening at record level, so
>> only
>> if the multimasters all hit the same record is there the potential for
>> lock
>> conflict.
>> Why will dB's being randomly used, hit the same records, I think its a
>> low
>> probability to begin with?
>
> That's only true if you are certain that the update pattern is NOT
> involving a shared set of records.  IN GENERAL, heavy write activity
> can cause locking to become mighty expensive, which is certainly a
> true statement.
>
>> Not happy with that, I wrote a multithreaded routine and got them to all
>> smack the same record, it NEVER ROLLED BACK, and if there is performance
>> degradation, I didnt notice it... again probably a testament to the MVCC
>> design.
>
> It seems likely to me that this requires some careful validation of
> testing.
>
> An effect we see is that if a set of transactions are "fighting" over
> a single "balance" record, they will essentially serialize over that.
>
> On a system with a single CPU, it is not obvious that you'll see a
> degradation there because, since you only have the single CPU, it
> would be serializing the activity anyways.
>
> Try it out on an 8-way SMP system and you may see things differently.
>
>> In any event if you look at the documentation, you'll see SPAR is not
>> multimaster or nothing. Can use say one server in an office and another
>> to
>> pump data to a remote web site... not sure if you would even call that
>> multimaster, thats the point, I'm not sure SPAR fits any pure theory
>> category.
>
> There are a few tests I could throw at it that tend to challenge
> replication systems vis-a-vis "fidelity of results."  I otta see if I
> can find them in a readily deployable form.
>
> There are two notable anomalies which have been known to break
> replication systems:
>
> 1.  Nondeterministic updates:
>
> For instance, functions that are nondeterministic:
>
>  insert into rtable values (random(), now());
>
> Or result sets that are nondeterministic:
>
>  insert into rtable2 (select * from mytable where some_attr='foo'
>     order by random() limit 5);   -- Where there are 25 records with
> some_attr='foo'
>
> 2.  Value swapping:
>
> Consider the table:
>
> create table t1 (mk integer primary key, val text unique not null);
>
> insert into t1 (mk, val) values (1, 'chris');
> insert into t1 (mk, val) values (2, 'dave');
> insert into t1 (mk, val) values (3, 'brad');
>
> begin;
> update t1 set mk = 99 where mk = 1;
> update t1 set mk = 1 where mk = 3;
> update t1 set mk = 3 where mk = 99;
> commit;
>
> Is there a condition where a pause somewhere in there will cause
> replication to break?  Note that there have been replication systems
> (erServer) that this set of updates can, intermittently, cause to fall
> over.
> --
> let name="cbbrowne" and tld=" linuxfinances.info" in String.concat "@"
> [name;tld];;
> http://cbbrowne.com/info/slony.html
> "Feel free to  contact me (flames about my english  and the useless of
> this driver will be redirected to /dev/null, oh no, it's full...)"
> -- Michael Beck, describing the PC-speaker sound device
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: Don't 'kill -9' the postmaster
>


---------------------------(end of broadcast)---------------------------
TIP 5: don't forget to increase your free space map settings

Yes, that is true with pgpool. I did face the same as well.

There is another as well Uni-Cluster ( http://www.continuent.com/index.php?option=com_content&task=view&id=213&Itemid=170 ), haven't tried yet but it might help you there...

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

On 12/26/06, Andy Dale <andy.dale@gmail.com> wrote:

The issue i had with pgpool (1 or 2) was that (correct me if i am wrong) you had to start the pgpool cluster with both nodes in the same state.  I thought this would mean that if you had a DB fail, before you could re-introduce it into the pgpool cluster you would have to manually sync it with the cluster state, is this correct ??

The system i need multi master sync for is highly transactional, so if the behaviour i stated above is correct it is not suitable.  I have tried s-lony, and while i was pleased with the performance, it is only Single Master - Multi Slave which is not acceptable as well.

Andy

On 26/12/06, Shoaib Mir <shoaibmir@gmail.com > wrote:

pgpool-II might help you there too I guess...

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

On 12/26/06, Andy Dale <andy.dale@gmail.com> wrote:

Hi,

I have just read the statement that Postgres does have (with end user assembly) multi-master replication system.  Is this just PGCluster or something else ? if it is not PGCluster, then how can this be achieved ?

Cheers,

Andy

On 24/12/06, Shoaib Mir < shoaibmir@gmail.com> wrote:

I guess the latest 8.2 Windows PostgreSQL installer does come with a Slony option and you can set it up easily using pgadmin too.

This link --> http://people.planetpostgresql.org/xzilla/index.php?/archives/200-Alpha-testing-Slony-on-win32-Crib-Notes.html might help you as well.

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

On 12/25/06, org@kewlstuff.co.za <org@kewlstuff.co.za> wrote:

Thanks Chris,
I see you a core member of Slony team and a replication guru so I'll look
into it.
I'm not slamming Slony I think its probably the right tool for type of work
your company Afilias does. Just wish you would make an official Windows
version of Slony as well.
Anyway thanks for the education, and I think it would be a good thing if
your site on replication, was also listed on Postgresql... good research.
Merry Xmas

----- Original Message -----
From: "Christopher Browne" <cbbrowne@acm.org>
To: < pgsql-general@postgresql.org>
Sent: Sunday, December 24, 2006 4:23 AM
Subject: Re: [GENERAL] Clustering & Load Balancing & Replication


> Centuries ago, Nostradamus foresaw when org@kewlstuff.co.za would write:
>> Suggest you download my little application and read the documentation,
>> you'll see its very different, maybe even interesting.
>> Maybe they should change that to.... Postgres DOES HAVE a free
>> multi-master
>> replication system :)
>
> It isn't systematically usable as such, without a whole lot of
> end-user assembly.
>
>> One comment they make.... "Heavy write activity can cause excessive
>> locking,
>> leading to poor performance. In fact, write performance is often worse
>> than
>> that of a single server. Read requests can be sent to any server."
>> I'm not sure I agree with that... or maybe MVCC is just fantastic.... I
>> tested it.
>> The 2 phase commit locking is definitely happening at record level, so
>> only
>> if the multimasters all hit the same record is there the potential for
>> lock
>> conflict.
>> Why will dB's being randomly used, hit the same records, I think its a
>> low
>> probability to begin with?
>
> That's only true if you are certain that the update pattern is NOT
> involving a shared set of records.  IN GENERAL, heavy write activity
> can cause locking to become mighty expensive, which is certainly a
> true statement.
>
>> Not happy with that, I wrote a multithreaded routine and got them to all
>> smack the same record, it NEVER ROLLED BACK, and if there is performance
>> degradation, I didnt notice it... again probably a testament to the MVCC
>> design.
>
> It seems likely to me that this requires some careful validation of
> testing.
>
> An effect we see is that if a set of transactions are "fighting" over
> a single "balance" record, they will essentially serialize over that.
>
> On a system with a single CPU, it is not obvious that you'll see a
> degradation there because, since you only have the single CPU, it
> would be serializing the activity anyways.
>
> Try it out on an 8-way SMP system and you may see things differently.
>
>> In any event if you look at the documentation, you'll see SPAR is not
>> multimaster or nothing. Can use say one server in an office and another
>> to
>> pump data to a remote web site... not sure if you would even call that
>> multimaster, thats the point, I'm not sure SPAR fits any pure theory
>> category.
>
> There are a few tests I could throw at it that tend to challenge
> replication systems vis-a-vis "fidelity of results."  I otta see if I
> can find them in a readily deployable form.
>
> There are two notable anomalies which have been known to break
> replication systems:
>
> 1.  Nondeterministic updates:
>
> For instance, functions that are nondeterministic:
>
>  insert into rtable values (random(), now());
>
> Or result sets that are nondeterministic:
>
>  insert into rtable2 (select * from mytable where some_attr='foo'
>     order by random() limit 5);   -- Where there are 25 records with
> some_attr='foo'
>
> 2.  Value swapping:
>
> Consider the table:
>
> create table t1 (mk integer primary key, val text unique not null);
>
> insert into t1 (mk, val) values (1, 'chris');
> insert into t1 (mk, val) values (2, 'dave');
> insert into t1 (mk, val) values (3, 'brad');
>
> begin;
> update t1 set mk = 99 where mk = 1;
> update t1 set mk = 1 where mk = 3;
> update t1 set mk = 3 where mk = 99;
> commit;
>
> Is there a condition where a pause somewhere in there will cause
> replication to break?  Note that there have been replication systems
> (erServer) that this set of updates can, intermittently, cause to fall
> over.
> --
> let name="cbbrowne" and tld=" linuxfinances.info" in String.concat "@"
> [name;tld];;
> http://cbbrowne.com/info/slony.html
> "Feel free to  contact me (flames about my english  and the useless of
> this driver will be redirected to /dev/null, oh no, it's full...)"
> -- Michael Beck, describing the PC-speaker sound device
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: Don't 'kill -9' the postmaster
>


---------------------------(end of broadcast)---------------------------
TIP 5: don't forget to increase your free space map settings

The company i am working for has a trail/evaluation license for p/cluster, but unfortunately i cannot get it to function as a JBoss datasource.

Cheers,

Andy

On 26/12/06, Shoaib Mir <shoaibmir@gmail.com> wrote:

Yes, that is true with pgpool. I did face the same as well.

There is another as well Uni-Cluster ( http://www.continuent.com/index.php?option=com_content&task=view&id=213&Itemid=170 ), haven't tried yet but it might help you there...

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

On 12/26/06, Andy Dale <andy.dale@gmail.com> wrote:

The issue i had with pgpool (1 or 2) was that (correct me if i am wrong) you had to start the pgpool cluster with both nodes in the same state.  I thought this would mean that if you had a DB fail, before you could re-introduce it into the pgpool cluster you would have to manually sync it with the cluster state, is this correct ??

The system i need multi master sync for is highly transactional, so if the behaviour i stated above is correct it is not suitable.  I have tried s-lony, and while i was pleased with the performance, it is only Single Master - Multi Slave which is not acceptable as well.

Andy

On 26/12/06, Shoaib Mir <shoaibmir@gmail.com > wrote:

pgpool-II might help you there too I guess...

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

On 12/26/06, Andy Dale <andy.dale@gmail.com> wrote:

Hi,

I have just read the statement that Postgres does have (with end user assembly) multi-master replication system.  Is this just PGCluster or something else ? if it is not PGCluster, then how can this be achieved ?

Cheers,

Andy

On 24/12/06, Shoaib Mir < shoaibmir@gmail.com> wrote:

I guess the latest 8.2 Windows PostgreSQL installer does come with a Slony option and you can set it up easily using pgadmin too.

This link --> http://people.planetpostgresql.org/xzilla/index.php?/archives/200-Alpha-testing-Slony-on-win32-Crib-Notes.html might help you as well.

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

On 12/25/06, org@kewlstuff.co.za <org@kewlstuff.co.za> wrote:

Thanks Chris,
I see you a core member of Slony team and a replication guru so I'll look
into it.
I'm not slamming Slony I think its probably the right tool for type of work
your company Afilias does. Just wish you would make an official Windows
version of Slony as well.
Anyway thanks for the education, and I think it would be a good thing if
your site on replication, was also listed on Postgresql... good research.
Merry Xmas

----- Original Message -----
From: "Christopher Browne" <cbbrowne@acm.org>
To: < pgsql-general@postgresql.org>
Sent: Sunday, December 24, 2006 4:23 AM
Subject: Re: [GENERAL] Clustering & Load Balancing & Replication


> Centuries ago, Nostradamus foresaw when org@kewlstuff.co.za would write:
>> Suggest you download my little application and read the documentation,
>> you'll see its very different, maybe even interesting.
>> Maybe they should change that to.... Postgres DOES HAVE a free
>> multi-master
>> replication system :)
>
> It isn't systematically usable as such, without a whole lot of
> end-user assembly.
>
>> One comment they make.... "Heavy write activity can cause excessive
>> locking,
>> leading to poor performance. In fact, write performance is often worse
>> than
>> that of a single server. Read requests can be sent to any server."
>> I'm not sure I agree with that... or maybe MVCC is just fantastic.... I
>> tested it.
>> The 2 phase commit locking is definitely happening at record level, so
>> only
>> if the multimasters all hit the same record is there the potential for
>> lock
>> conflict.
>> Why will dB's being randomly used, hit the same records, I think its a
>> low
>> probability to begin with?
>
> That's only true if you are certain that the update pattern is NOT
> involving a shared set of records.  IN GENERAL, heavy write activity
> can cause locking to become mighty expensive, which is certainly a
> true statement.
>
>> Not happy with that, I wrote a multithreaded routine and got them to all
>> smack the same record, it NEVER ROLLED BACK, and if there is performance
>> degradation, I didnt notice it... again probably a testament to the MVCC
>> design.
>
> It seems likely to me that this requires some careful validation of
> testing.
>
> An effect we see is that if a set of transactions are "fighting" over
> a single "balance" record, they will essentially serialize over that.
>
> On a system with a single CPU, it is not obvious that you'll see a
> degradation there because, since you only have the single CPU, it
> would be serializing the activity anyways.
>
> Try it out on an 8-way SMP system and you may see things differently.
>
>> In any event if you look at the documentation, you'll see SPAR is not
>> multimaster or nothing. Can use say one server in an office and another
>> to
>> pump data to a remote web site... not sure if you would even call that
>> multimaster, thats the point, I'm not sure SPAR fits any pure theory
>> category.
>
> There are a few tests I could throw at it that tend to challenge
> replication systems vis-a-vis "fidelity of results."  I otta see if I
> can find them in a readily deployable form.
>
> There are two notable anomalies which have been known to break
> replication systems:
>
> 1.  Nondeterministic updates:
>
> For instance, functions that are nondeterministic:
>
>  insert into rtable values (random(), now());
>
> Or result sets that are nondeterministic:
>
>  insert into rtable2 (select * from mytable where some_attr='foo'
>     order by random() limit 5);   -- Where there are 25 records with
> some_attr='foo'
>
> 2.  Value swapping:
>
> Consider the table:
>
> create table t1 (mk integer primary key, val text unique not null);
>
> insert into t1 (mk, val) values (1, 'chris');
> insert into t1 (mk, val) values (2, 'dave');
> insert into t1 (mk, val) values (3, 'brad');
>
> begin;
> update t1 set mk = 99 where mk = 1;
> update t1 set mk = 1 where mk = 3;
> update t1 set mk = 3 where mk = 99;
> commit;
>
> Is there a condition where a pause somewhere in there will cause
> replication to break?  Note that there have been replication systems
> (erServer) that this set of updates can, intermittently, cause to fall
> over.
> --
> let name="cbbrowne" and tld=" linuxfinances.info" in String.concat "@"
> [name;tld];;
> http://cbbrowne.com/info/slony.html
> "Feel free to  contact me (flames about my english  and the useless of
> this driver will be redirected to /dev/null, oh no, it's full...)"
> -- Michael Beck, describing the PC-speaker sound device
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: Don't 'kill -9' the postmaster
>


---------------------------(end of broadcast)---------------------------
TIP 5: don't forget to increase your free space map settings

Why are you going for a multimaster case here? are you doing it for load balancing? if then you can also do it horizontally with a multi disk setup... Slony can be a real good candidate here as well with Linux HA in combination.

For going on a vertical solution you can try OpenSSI and see if that can work for you, haven't tried that myself but will like to hear about PostgreSQL configuration with OpenSSI

-------------------

Shoaib Mir
EnterpriseDB ( www.enterprisedb.com)

On 12/26/06, Andy Dale < andy.dale@gmail.com> wrote:

The company i am working for has a trail/evaluation license for p/cluster, but unfortunately i cannot get it to function as a JBoss datasource.

Cheers,

Andy

On 26/12/06, Shoaib Mir <shoaibmir@gmail.com> wrote:

Yes, that is true with pgpool. I did face the same as well.

There is another as well Uni-Cluster ( http://www.continuent.com/index.php?option=com_content&task=view&id=213&Itemid=170 ), haven't tried yet but it might help you there...

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

On 12/26/06, Andy Dale <andy.dale@gmail.com> wrote:

The issue i had with pgpool (1 or 2) was that (correct me if i am wrong) you had to start the pgpool cluster with both nodes in the same state.  I thought this would mean that if you had a DB fail, before you could re-introduce it into the pgpool cluster you would have to manually sync it with the cluster state, is this correct ??

The system i need multi master sync for is highly transactional, so if the behaviour i stated above is correct it is not suitable.  I have tried s-lony, and while i was pleased with the performance, it is only Single Master - Multi Slave which is not acceptable as well.

Andy

On 26/12/06, Shoaib Mir <shoaibmir@gmail.com > wrote:

pgpool-II might help you there too I guess...

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

On 12/26/06, Andy Dale <andy.dale@gmail.com> wrote:

Hi,

I have just read the statement that Postgres does have (with end user assembly) multi-master replication system.  Is this just PGCluster or something else ? if it is not PGCluster, then how can this be achieved ?

Cheers,

Andy

On 24/12/06, Shoaib Mir < shoaibmir@gmail.com> wrote:

I guess the latest 8.2 Windows PostgreSQL installer does come with a Slony option and you can set it up easily using pgadmin too.

This link --> http://people.planetpostgresql.org/xzilla/index.php?/archives/200-Alpha-testing-Slony-on-win32-Crib-Notes.html might help you as well.

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

On 12/25/06, org@kewlstuff.co.za <org@kewlstuff.co.za> wrote:

Thanks Chris,
I see you a core member of Slony team and a replication guru so I'll look
into it.
I'm not slamming Slony I think its probably the right tool for type of work
your company Afilias does. Just wish you would make an official Windows
version of Slony as well.
Anyway thanks for the education, and I think it would be a good thing if
your site on replication, was also listed on Postgresql... good research.
Merry Xmas

----- Original Message -----
From: "Christopher Browne" <cbbrowne@acm.org>
To: < pgsql-general@postgresql.org>
Sent: Sunday, December 24, 2006 4:23 AM
Subject: Re: [GENERAL] Clustering & Load Balancing & Replication


> Centuries ago, Nostradamus foresaw when org@kewlstuff.co.za would write:
>> Suggest you download my little application and read the documentation,
>> you'll see its very different, maybe even interesting.
>> Maybe they should change that to.... Postgres DOES HAVE a free
>> multi-master
>> replication system :)
>
> It isn't systematically usable as such, without a whole lot of
> end-user assembly.
>
>> One comment they make.... "Heavy write activity can cause excessive
>> locking,
>> leading to poor performance. In fact, write performance is often worse
>> than
>> that of a single server. Read requests can be sent to any server."
>> I'm not sure I agree with that... or maybe MVCC is just fantastic.... I
>> tested it.
>> The 2 phase commit locking is definitely happening at record level, so
>> only
>> if the multimasters all hit the same record is there the potential for
>> lock
>> conflict.
>> Why will dB's being randomly used, hit the same records, I think its a
>> low
>> probability to begin with?
>
> That's only true if you are certain that the update pattern is NOT
> involving a shared set of records.  IN GENERAL, heavy write activity
> can cause locking to become mighty expensive, which is certainly a
> true statement.
>
>> Not happy with that, I wrote a multithreaded routine and got them to all
>> smack the same record, it NEVER ROLLED BACK, and if there is performance
>> degradation, I didnt notice it... again probably a testament to the MVCC
>> design.
>
> It seems likely to me that this requires some careful validation of
> testing.
>
> An effect we see is that if a set of transactions are "fighting" over
> a single "balance" record, they will essentially serialize over that.
>
> On a system with a single CPU, it is not obvious that you'll see a
> degradation there because, since you only have the single CPU, it
> would be serializing the activity anyways.
>
> Try it out on an 8-way SMP system and you may see things differently.
>
>> In any event if you look at the documentation, you'll see SPAR is not
>> multimaster or nothing. Can use say one server in an office and another
>> to
>> pump data to a remote web site... not sure if you would even call that
>> multimaster, thats the point, I'm not sure SPAR fits any pure theory
>> category.
>
> There are a few tests I could throw at it that tend to challenge
> replication systems vis-a-vis "fidelity of results."  I otta see if I
> can find them in a readily deployable form.
>
> There are two notable anomalies which have been known to break
> replication systems:
>
> 1.  Nondeterministic updates:
>
> For instance, functions that are nondeterministic:
>
>  insert into rtable values (random(), now());
>
> Or result sets that are nondeterministic:
>
>  insert into rtable2 (select * from mytable where some_attr='foo'
>     order by random() limit 5);   -- Where there are 25 records with
> some_attr='foo'
>
> 2.  Value swapping:
>
> Consider the table:
>
> create table t1 (mk integer primary key, val text unique not null);
>
> insert into t1 (mk, val) values (1, 'chris');
> insert into t1 (mk, val) values (2, 'dave');
> insert into t1 (mk, val) values (3, 'brad');
>
> begin;
> update t1 set mk = 99 where mk = 1;
> update t1 set mk = 1 where mk = 3;
> update t1 set mk = 3 where mk = 99;
> commit;
>
> Is there a condition where a pause somewhere in there will cause
> replication to break?  Note that there have been replication systems
> (erServer) that this set of updates can, intermittently, cause to fall
> over.
> --
> let name="cbbrowne" and tld=" linuxfinances.info" in String.concat "@"
> [name;tld];;
> http://cbbrowne.com/info/slony.html
> "Feel free to  contact me (flames about my english  and the useless of
> this driver will be redirected to /dev/null, oh no, it's full...)"
> -- Michael Beck, describing the PC-speaker sound device
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: Don't 'kill -9' the postmaster
>


---------------------------(end of broadcast)---------------------------
TIP 5: don't forget to increase your free space map settings

We are trying to achieve High Availability over load balancing, so basically we always try and have 2 databases in the same state while both are active, and if one goes down it should (hopefully) failover seemlessly.  Thanks for the info on OpenSSI, as i had not heard of this before and will look into it further.

Cheers,

Andy

On 26/12/06, Shoaib Mir < shoaibmir@gmail.com> wrote:

Why are you going for a multimaster case here? are you doing it for load balancing? if then you can also do it horizontally with a multi disk setup... Slony can be a real good candidate here as well with Linux HA in combination.

For going on a vertical solution you can try OpenSSI and see if that can work for you, haven't tried that myself but will like to hear about PostgreSQL configuration with OpenSSI

-------------------

Shoaib Mir
EnterpriseDB ( www.enterprisedb.com)

On 12/26/06, Andy Dale < andy.dale@gmail.com> wrote:

The company i am working for has a trail/evaluation license for p/cluster, but unfortunately i cannot get it to function as a JBoss datasource.

Cheers,

Andy

On 26/12/06, Shoaib Mir <shoaibmir@gmail.com> wrote:

Yes, that is true with pgpool. I did face the same as well.

There is another as well Uni-Cluster ( http://www.continuent.com/index.php?option=com_content&task=view&id=213&Itemid=170 ), haven't tried yet but it might help you there...

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

On 12/26/06, Andy Dale <andy.dale@gmail.com> wrote:

The issue i had with pgpool (1 or 2) was that (correct me if i am wrong) you had to start the pgpool cluster with both nodes in the same state.  I thought this would mean that if you had a DB fail, before you could re-introduce it into the pgpool cluster you would have to manually sync it with the cluster state, is this correct ??

The system i need multi master sync for is highly transactional, so if the behaviour i stated above is correct it is not suitable.  I have tried s-lony, and while i was pleased with the performance, it is only Single Master - Multi Slave which is not acceptable as well.

Andy

On 26/12/06, Shoaib Mir <shoaibmir@gmail.com > wrote:

pgpool-II might help you there too I guess...

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

On 12/26/06, Andy Dale <andy.dale@gmail.com> wrote:

Hi,

I have just read the statement that Postgres does have (with end user assembly) multi-master replication system.  Is this just PGCluster or something else ? if it is not PGCluster, then how can this be achieved ?

Cheers,

Andy

On 24/12/06, Shoaib Mir < shoaibmir@gmail.com> wrote:

I guess the latest 8.2 Windows PostgreSQL installer does come with a Slony option and you can set it up easily using pgadmin too.

This link --> http://people.planetpostgresql.org/xzilla/index.php?/archives/200-Alpha-testing-Slony-on-win32-Crib-Notes.html might help you as well.

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

On 12/25/06, org@kewlstuff.co.za <org@kewlstuff.co.za> wrote:

Thanks Chris,
I see you a core member of Slony team and a replication guru so I'll look
into it.
I'm not slamming Slony I think its probably the right tool for type of work
your company Afilias does. Just wish you would make an official Windows
version of Slony as well.
Anyway thanks for the education, and I think it would be a good thing if
your site on replication, was also listed on Postgresql... good research.
Merry Xmas

----- Original Message -----
From: "Christopher Browne" <cbbrowne@acm.org>
To: < pgsql-general@postgresql.org>
Sent: Sunday, December 24, 2006 4:23 AM
Subject: Re: [GENERAL] Clustering & Load Balancing & Replication


> Centuries ago, Nostradamus foresaw when org@kewlstuff.co.za would write:
>> Suggest you download my little application and read the documentation,
>> you'll see its very different, maybe even interesting.
>> Maybe they should change that to.... Postgres DOES HAVE a free
>> multi-master
>> replication system :)
>
> It isn't systematically usable as such, without a whole lot of
> end-user assembly.
>
>> One comment they make.... "Heavy write activity can cause excessive
>> locking,
>> leading to poor performance. In fact, write performance is often worse
>> than
>> that of a single server. Read requests can be sent to any server."
>> I'm not sure I agree with that... or maybe MVCC is just fantastic.... I
>> tested it.
>> The 2 phase commit locking is definitely happening at record level, so
>> only
>> if the multimasters all hit the same record is there the potential for
>> lock
>> conflict.
>> Why will dB's being randomly used, hit the same records, I think its a
>> low
>> probability to begin with?
>
> That's only true if you are certain that the update pattern is NOT
> involving a shared set of records.  IN GENERAL, heavy write activity
> can cause locking to become mighty expensive, which is certainly a
> true statement.
>
>> Not happy with that, I wrote a multithreaded routine and got them to all
>> smack the same record, it NEVER ROLLED BACK, and if there is performance
>> degradation, I didnt notice it... again probably a testament to the MVCC
>> design.
>
> It seems likely to me that this requires some careful validation of
> testing.
>
> An effect we see is that if a set of transactions are "fighting" over
> a single "balance" record, they will essentially serialize over that.
>
> On a system with a single CPU, it is not obvious that you'll see a
> degradation there because, since you only have the single CPU, it
> would be serializing the activity anyways.
>
> Try it out on an 8-way SMP system and you may see things differently.
>
>> In any event if you look at the documentation, you'll see SPAR is not
>> multimaster or nothing. Can use say one server in an office and another
>> to
>> pump data to a remote web site... not sure if you would even call that
>> multimaster, thats the point, I'm not sure SPAR fits any pure theory
>> category.
>
> There are a few tests I could throw at it that tend to challenge
> replication systems vis-a-vis "fidelity of results."  I otta see if I
> can find them in a readily deployable form.
>
> There are two notable anomalies which have been known to break
> replication systems:
>
> 1.  Nondeterministic updates:
>
> For instance, functions that are nondeterministic:
>
>  insert into rtable values (random(), now());
>
> Or result sets that are nondeterministic:
>
>  insert into rtable2 (select * from mytable where some_attr='foo'
>     order by random() limit 5);   -- Where there are 25 records with
> some_attr='foo'
>
> 2.  Value swapping:
>
> Consider the table:
>
> create table t1 (mk integer primary key, val text unique not null);
>
> insert into t1 (mk, val) values (1, 'chris');
> insert into t1 (mk, val) values (2, 'dave');
> insert into t1 (mk, val) values (3, 'brad');
>
> begin;
> update t1 set mk = 99 where mk = 1;
> update t1 set mk = 1 where mk = 3;
> update t1 set mk = 3 where mk = 99;
> commit;
>
> Is there a condition where a pause somewhere in there will cause
> replication to break?  Note that there have been replication systems
> (erServer) that this set of updates can, intermittently, cause to fall
> over.
> --
> let name="cbbrowne" and tld=" linuxfinances.info" in String.concat "@"
> [name;tld];;
> http://cbbrowne.com/info/slony.html
> "Feel free to  contact me (flames about my english  and the useless of
> this driver will be redirected to /dev/null, oh no, it's full...)"
> -- Michael Beck, describing the PC-speaker sound device
>
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