postgres-xc-general Mailing List for Postgres-XC

On 10/5/2013 5:19 PM, Michael Paquier wrote:
> On Sat, Oct 5, 2013 at 9:00 PM, Stefan Lekov <ar...@er...> wrote:
>> Hello, I'm new to the Postgres-XC project. In fact I am still
>> considering if I should install it in order to try it as a
>> replacement of my current database clusters (those are based around
>> MySQL and its binary_log based replication).
> Have you considered PostgreSQL as a potential solution before
> Postgres-XC. Why do you especially need XC?
I have used PosgreSQL in the past, I am using it at the moment (for 
other projects) and I'd like to continue using in the future. My current 
requirements are including having a multi-master replicated database 
cluster. These requirements are related to redundancy and possible 
scalability. While one PostgreSQL server will cope with any load that I 
can throw at it for the near future, that might not be the case in about 
an year or two. As for the redundancy part - I am familiar with 
PostgreSQL capabilities of a warm standby server however I am looking 
for something more robust.

Because of the requirement of "multi-master", I am investigating 
Postgres-XC and pgpool2 capabilities to deliver such system. I can 
migrate to a single PostgreSQL server, however I am not really keen on 
solving the replication dilemma on-the-fly when the system is already 
running with Postgres - I prefer having something that is already 
working as expected right from the start.

>> Before actually starting the installation of postgres-xc I would like
>> to know what is the procedure for restarting nodes. I have already
>> read a few documents/mails regarding restoring or resyncing a failed
>> datanode, however these documents does not answer my simple question:
>> What should be the procedure for rebooting servers? For example I
>> have a kernel updated pending (due to security reasons) - I'm
>> installing the new kernel, but I have to reboot all machine.
>> Theoretically all nodes (both coordinators and datanodes) are working
>> on different physical servers or VMes. In a perfect scenario I would
>> like to keep the system in production while I am restarting the
>> servers one by one. However I am not sure what would be the effect of
>> rebooting servers one by one.
> If a node is restarted or facing an outage, all the transactions it
> needs to be involved in will simply fail. In the case of Coordinator,
> this has effect only for DDL. For Datanodes, this has effect as well
> for DDL, but also for DML and SELECT of the node is needed for the
> transaction.
There would be no DDL during these operations. I can limit the queries 
to DML only.
>> For purpose of example let me have four datanodes: A,B,C,D All
>> servers are synced and are operating as expected. 1) Upgrade A,
>> reboot A 2) INSERT/UPDATE/DELETE queries 3) A boots up and is
>> successfully started 4) INSERT/UPDATE/DELETE queries 5) Upgrade B,
>> reboot B ... ... As for the "Coordinators" nodes. How are those
>> affected by temporary stopping and restarting the postgres-xc related
>> services. What should be the load balancer in front of these servers
>> in order to be able to both load-balance and fail-over if one of the
>> Coordinators is offline either due to failed server or due to
>> rebooting servers.
> DDLs won't work. Applications will use one access point. In this case
> no problems for your application, connect to the other Coordinators to
> execute queries as long as they are not DDLs.
What system, application or method would you recommend for performing 
the load-balance/fail-over of connections to the Coordinators.
>> I have no problem with relatively heavy operation of full restore of
>> a datanode in event of failed server. Such restoration operation can
>> be properly scheduled and executed, however I am interested how would
>> postgres-xc react to simple scenarioa simple operation of restarting
>> a server due to whatever reasons should
> As mentioned above, transactions that will need it will simply fail.
> You could always failover a slave for the outage period if necessary.
Correct me if I'm wrong: All data (read databases, schema, tables, etc) 
would be replicated to all datanodes. So before host A goes down all 
servers would have the same dataset. This way no transaction should fail 
due to the missing datanode A. While A has been booting up several 
transactions have passed (since such restart is an operation I can 
schedule, I'm doing that during time when we have low to no load on our 
systems, thus the transaction count is relatively low). My question is 
how to bring A back to having "the same dataset" as the rest of the 
datanodes before I can continue with the next host/datanode?

Regards,
Stefan Lekov

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On Wed, Oct 9, 2013 at 9:54 PM, Hector M. Jacas <hec...@et...>wrote:

>  Hi all,
>
> First I must apologize because obviously I was reading the document
> oriented to bash version of pgxc_ctl.
>
> In the documentation of the binary version there is no reference to these
> facilities (dropdb/dropuser). This is the one I should have read .
>
> My mistake and my apologies .
>
> I beg your patience and condescension when from the user role of this
> great project I take the liberty to comment the answer to my post .
>
> I do not share the view of Mr. Ashutosh Bapat when he says " is not an
> interface pgxc_ctl for dropping database or user. " reason: "It's just a
> cluster management utility "
>
> I think there is an inconsistency in that statement because the same
> reason for not including dropdb and dropuser commands are perfectly valid
> createdb and createuser .
>

There is difference between what is supported as a requirement and what is
supported because it fits well in the utility. You may compare pgxc_ctl
with pg_ctl, which basically allow controlling the life of server. pgxc_ctl
being made for XC, has to support life of a cluster and allows controlling
individual server. On top, it allows creating a cluster, (which is not
required in pg_ctl, initdb does it). This particular functionality needs
Createdb and Createuser, so does it support those. But a user should not
look at pgxc_ctl for managing individual databases. The server is more than
capable of doing it and that functionality can be accessed through
connectors or utilities like create* or drop*.


>
> You as project developers ( or contribution ) decide the philosophy with
> which your product works and I in my role as user I should be able to
> reconcile my working methods with the philosophy of the tools I have
> selected.
>
> POSTGRESXC is a great project because it solves big problems.
>
> PGXC_CTL is another great project because it simplifies the deployment and
> management of postgresxc and if you add shortcuts to frequently used
> commands (and perhaps, some security features) this project could become a
> kind of Central Command for POSTGRESXC .
>
> Thank you very much for your answers ,
>
> Hector M. Jacas
>
>
>
>
> On 10/09/2013 12:12 AM, Ashutosh Bapat wrote:
>
>  Hector,
>  AFAIK, pgxc_ctl is not an interface for dropping database or user. It's
> just a cluster management utility. You should use corresponding binaries or
> SQL commands for that purpose.
>
>
> On Tue, Oct 8, 2013 at 9:32 PM, Hector M. Jacas <hec...@et...>wrote:
>
>>
>> Hi all,
>>
>> Among the features described in:
>> https://github.com/koichi-szk/PGXC-Tools/blob/master/pgxc_ctl/manual.txtis deleting the databases (Dropdb) and users (Dropuser) and when I try make
>> use of these commands pgxc_ctl answers: command not found
>>
>> PGXC Createdb testdb
>> Selected coord2.
>> PGXC Dropdb testdb
>> sh: Dropdb: command not found
>> PGXC Createuser usertest1
>> Selected coord1.
>> PGXC Dropuser usertest1
>> sh: Dropuser: command not found
>> PGXC
>>
>> Carefully review the source code and found that in the folder:
>> postgres-xc/contrib/pgxc_ctl , there is a file (do_command.c) in which
>> reference is made and performed the execution of Createdb (line 2339) and
>> Createuser (line 2369).
>>
>> In this file there is no reference whatsoever to Dropdb or Dropuser .
>>
>> There is another file (in the same directory) called: pgxc_ctl.bash, in
>> which reference is made and run the corresponding command to Createdb,
>> Dropdb, Createuser and Dropuser.
>>
>> Do not remember reading during pgxc compliacion and deployment (or
>> pgxc_ctl in the area of contributions ) anything regarding how to handle
>> this situation.
>>
>> How to resolve this issue?
>>
>> The pgxc_ctl in its binary version lacks Dropdb and Dropuser commands?
>> I must choose between the binary version and the version bash? What would
>> be the impact of this change ?
>>
>> Can anyone guide me please
>>
>> Thanks in advance,
>>
>> Hector M. Jacas
>>
>> ---
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>>
>>
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>> Free Intel webinars can help you accelerate application performance.
>> Explore tips for MPI, OpenMP, advanced profiling, and more. Get the most
>> from
>> the latest Intel processors and coprocessors. See abstracts and register >
>>
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>> _______________________________________________
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>> Pos...@li...
>> https://lists.sourceforge.net/lists/listinfo/postgres-xc-general
>>
>>
>
>
> --
> Best Wishes,
> Ashutosh Bapat
> EnterpriseDB Corporation
> The Postgres Database Company
>
>
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-- 
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company

Please do not worry about it.   It is more than happy to hear any
requirements/good to have things.   Pgxc_ctl is not a complicated product
and you can submit patches.

Regards;

---
Koichi Suzuki


2013/10/10 Hector M. Jacas <hec...@et...>

>  Hi all,
>
> First I must apologize because obviously I was reading the document
> oriented to bash version of pgxc_ctl.
>
> In the documentation of the binary version there is no reference to these
> facilities (dropdb/dropuser). This is the one I should have read .
>
> My mistake and my apologies .
>
> I beg your patience and condescension when from the user role of this
> great project I take the liberty to comment the answer to my post .
>
> I do not share the view of Mr. Ashutosh Bapat when he says " is not an
> interface pgxc_ctl for dropping database or user. " reason: "It's just a
> cluster management utility "
>
> I think there is an inconsistency in that statement because the same
> reason for not including dropdb and dropuser commands are perfectly valid
> createdb and createuser .
>
> You as project developers ( or contribution ) decide the philosophy with
> which your product works and I in my role as user I should be able to
> reconcile my working methods with the philosophy of the tools I have
> selected.
>
> POSTGRESXC is a great project because it solves big problems.
>
> PGXC_CTL is another great project because it simplifies the deployment and
> management of postgresxc and if you add shortcuts to frequently used
> commands (and perhaps, some security features) this project could become a
> kind of Central Command for POSTGRESXC .
>
> Thank you very much for your answers ,
>
> Hector M. Jacas
>
>
>
>
> On 10/09/2013 12:12 AM, Ashutosh Bapat wrote:
>
>  Hector,
>  AFAIK, pgxc_ctl is not an interface for dropping database or user. It's
> just a cluster management utility. You should use corresponding binaries or
> SQL commands for that purpose.
>
>
> On Tue, Oct 8, 2013 at 9:32 PM, Hector M. Jacas <hec...@et...>wrote:
>
>>
>> Hi all,
>>
>> Among the features described in:
>> https://github.com/koichi-szk/PGXC-Tools/blob/master/pgxc_ctl/manual.txtis deleting the databases (Dropdb) and users (Dropuser) and when I try make
>> use of these commands pgxc_ctl answers: command not found
>>
>> PGXC Createdb testdb
>> Selected coord2.
>> PGXC Dropdb testdb
>> sh: Dropdb: command not found
>> PGXC Createuser usertest1
>> Selected coord1.
>> PGXC Dropuser usertest1
>> sh: Dropuser: command not found
>> PGXC
>>
>> Carefully review the source code and found that in the folder:
>> postgres-xc/contrib/pgxc_ctl , there is a file (do_command.c) in which
>> reference is made and performed the execution of Createdb (line 2339) and
>> Createuser (line 2369).
>>
>> In this file there is no reference whatsoever to Dropdb or Dropuser .
>>
>> There is another file (in the same directory) called: pgxc_ctl.bash, in
>> which reference is made and run the corresponding command to Createdb,
>> Dropdb, Createuser and Dropuser.
>>
>> Do not remember reading during pgxc compliacion and deployment (or
>> pgxc_ctl in the area of contributions ) anything regarding how to handle
>> this situation.
>>
>> How to resolve this issue?
>>
>> The pgxc_ctl in its binary version lacks Dropdb and Dropuser commands?
>> I must choose between the binary version and the version bash? What would
>> be the impact of this change ?
>>
>> Can anyone guide me please
>>
>> Thanks in advance,
>>
>> Hector M. Jacas
>>
>> ---
>> This message was processed by Kaspersky Mail Gateway 5.6.28/RELEASE
>> running at host imx3.etecsa.cu
>> Visit our web-site: <http://www.kaspersky.com>, <http://www.viruslist.com
>> >
>>
>>
>> ------------------------------------------------------------------------------
>> October Webinars: Code for Performance
>> Free Intel webinars can help you accelerate application performance.
>> Explore tips for MPI, OpenMP, advanced profiling, and more. Get the most
>> from
>> the latest Intel processors and coprocessors. See abstracts and register >
>>
>> http://pubads.g.doubleclick.net/gampad/clk?id=60134071&iu=/4140/ostg.clktrk
>> _______________________________________________
>> Postgres-xc-general mailing list
>> Pos...@li...
>> https://lists.sourceforge.net/lists/listinfo/postgres-xc-general
>>
>>
>
>
> --
> Best Wishes,
> Ashutosh Bapat
> EnterpriseDB Corporation
> The Postgres Database Company
>
>
> ---
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>
>
>
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>
>
> ------------------------------------------------------------------------------
> October Webinars: Code for Performance
> Free Intel webinars can help you accelerate application performance.
> Explore tips for MPI, OpenMP, advanced profiling, and more. Get the most
> from
> the latest Intel processors and coprocessors. See abstracts and register >
> http://pubads.g.doubleclick.net/gampad/clk?id=60134071&iu=/4140/ostg.clktrk
> _______________________________________________
> Postgres-xc-general mailing list
> Pos...@li...
> https://lists.sourceforge.net/lists/listinfo/postgres-xc-general
>
>