RE: Skipping schema changes in publication

On Wednesday, June 8, 2022 7:04 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Fri, Jun 3, 2022 at 3:37 PM vignesh C <vignesh21(at)gmail(dot)com> wrote:
> >
> > Thanks for the comments, the attached v8 patch has the changes for the
> same.
> >
>
> AFAICS, the summary of this proposal is that we want to support
> exclude of certain objects from publication with two kinds of
> variants. The first variant is to add support to exclude specific
> tables from ALL TABLES PUBLICATION. Without this feature, users need
> to manually add all tables for a database even when she wants to avoid
> only a handful of tables from the database say because they contain
> sensitive information or are not required. We have seen that other
> database like MySQL also provides similar feature [1] (See
> REPLICATE_WILD_IGNORE_TABLE). The proposed syntax for this is as
> follows:
>
> CREATE PUBLICATION pub1 FOR ALL TABLES EXCEPT TABLE t1,t2;
> or
> ALTER PUBLICATION pub1 ADD ALL TABLES EXCEPT TABLE t1,t2;
>
> This will allow us to publish all the tables in the current database
> except t1 and t2. Now, I see that pg_dump has a similar option
> provided by switch --exclude-table but that allows tables matching
> patterns which is not the case here. I am not sure if we need a
> similar variant here.
>
> Then users will be allowed to reset the publication by:
> ALTER PUBLICATION pub1 RESET;
>
> This will reset the publication to the default state which includes
> resetting the publication parameters, setting the ALL TABLES flag to
> false, and dropping the relations and schemas that are associated with
> the publication. I don't know if we want to go further with allowing
> to RESET specific parameters and if so which parameters and what would
> its syntax be?
>
> The second variant is to add support to exclude certain columns of a
> table while publishing a particular table. Currently, users need to
> list all required columns' names even if they don't want to hide most
> of the columns in the table (for example Create Publication pub For
> Table t1 (c1, c2)). Consider user doesn't want to publish the 'salary'
> or other sensitive information of executives/employees but would like
> to publish all other columns. I feel in such cases it will be a lot of
> work for the user especially when the table has many columns. I see
> that Oracle has a similar feature [2]. I think without this it will be
> difficult for users to use this feature in some cases. The patch for
> this is not proposed but I would imagine syntax for it to be something
> like "Create Publication pub For Table t1 Except (c3)" and similar
> variants for Alter Publication.

I think the feature to exclude certain columns of a table would be useful.

In some production scenarios, we usually do not want to replicate
sensitive fields(column) in the table. Although we already can achieve
this by specify all replicated columns in the list[1], but that seems a
hard work when the table has hundreds of columns.

[1]
CREATE TABLE test(a int, b int, c int,..., sensitive text);
CRAETE PUBLICATION pub FOR TABLE test(a,b,c,...);

In addition, it's not easy to maintain the column list like above. Because
we sometimes need to add new fields or delete fields due to business
needs. Every time we add a column(or delete a column in column list), we
need to update the column list.

If we support Except:
CRAETE PUBLICATION pub FOR TABLE test EXCEPT (sensitive);

We don't need to update the column list in most cases.

Thanks for "hametan" for providing the use case off-list.

Best regards,
Hou zj