Re: Fixed "Slony" related issues

On Mon, Aug 5, 2013 at 6:52 PM, Dave Page <dpage(at)pgadmin(dot)org> wrote:

> Hi
>
> On Mon, Aug 5, 2013 at 1:21 PM, Akshay Joshi
> <akshay(dot)joshi(at)enterprisedb(dot)com> wrote:
> > Hi Dave
> >
> > While testing pgAdmin with "Slony" I have found couple of following
> issues
> >
> > Found crash (segmentation fault) when create a new schema using slony
> > replication cluster. Crash is reproducible when user opens the "New
> > Schema..." dialog and select an slony cluster from "Use Slony" combo box
> and
> > click "OK".
> > DDL Statements like ( "CREATE SCHEMA" , "ALTER TABLE" ..) didn't work if
> > user select an slony cluster from "Use Slony" combo box and click "OK".
> >
> > I have analyze and fixed both the issues. Below is my analysis and
> solution
> >
> > Analysis for 1: - We have used wxComboBox for "Use Slony" option in the
> > dlgProperty dialog. To add an item into the combo box we have used
> "Append"
> > method of wxControlWithItems (wxComboBox is derived from
> > wxControlWithItems).
> >
> > According to the documentation of "wxControlWithItems" it is mention
> that in
> > the same control all items must have client data of the same type (typed
> or
> > untyped), if any. This type is determined by the first call to Append
> (the
> > version with client data pointer) or SetClientData. Attached is the
> > screenshot.
> >
> > In pgAdmin we have appended the wxEmptyString without any client data
> first
> > in the "Use Slony" combo box and then the slony cluster with client
> data. So
> > when the first append call gets executed, type of the client data is
> > determined as "Void *"
> >
> > Solution for 1:- There are two ways to solve this issue.
> >
> > Create a dummy object of client data(replClientData in our case) and
> passed
> > it when we append the wxEmptyString".
> > Typecast the "replClientData" to (void *) while appending the slony
> cluster.
> >
> > I have fixed it using the second option.
>
> OK.
>
> > Analysis for 2:- After fixing the above crash when we try to create the
> new
> > schema or add any new column to the existing table it neither applied to
> the
> > Master nor on Slave. As per the pgAdmin code if we select a slony cluster
> > then following two statements runs:
> >
> > SELECT _slonycluster.ddlscript_prepare(1, 0);
> > SELECT _slonycluster.ddlscript_complete(1, 'ALTER TABLE "Test" ADD COLUMN
> > isSlony boolean; ', 0);
> >
> > Where "p_only_on_node" parameter is set to 0. It is hard coded. Then I
> have
> > googled and found some example where this parameter is set to -1.
> >
> > I have analyze the code of "Slony 2.1.3 (slonik.c file) " and found that
> it
> > executes the following statement in sequence
> > SELECT _slonycluster.ddlscript_prepare(1, -1);
> > ALTER TABLE "Test" ADD COLUMN isSlony boolean;
> > SELECT _slonycluster.ddlscript_complete(1, 'ALTER TABLE "Test" ADD COLUMN
> > isSlony boolean; ', -1);
> >
> > Comparing it with pgAdmin code we execute only two
> > statements(ddlscript_prepare and ddlscript_complete) which is being used
> for
> > replication only, but there is no logic to execute the statement on
> Master
> > itself. May be my understanding here is wrong, please correct me.
> >
> >
> > Solution for 2:- To solve the above issue, First I have set the value of
> > "p_only_on_node" to -1 instead of 0 and then added the SQL which is
> going to
> > be executed on Master.
>
> Did you check that the modified version of the SQL is appropriate for
> all versions of Slony? We currently support back to 1.2 iirc.
>

I have tested my logic with Slony v2.1.3 and v2.0.7. For v1.2 I have
taken the source code and compare the slonik.c file with the v2.1.3 and it
seems to be working on that as well.

>
> Thanks.
>
> --
> Dave Page
> Blog: http://pgsnake.blogspot.com
> Twitter: @pgsnake
>
> EnterpriseDB UK: http://www.enterprisedb.com
> The Enterprise PostgreSQL Company
>

--
*Akshay Joshi
Senior Software Engineer
EnterpriseDB Corporation
The Enterprise PostgreSQL Company
Phone: +91 20-3058-9522
Mobile: +91 976-788-8246*