Column Filtering in Logical Replication

Hi,

Filtering of columns at the publisher node will allow for selective
replication of data between publisher and subscriber. In case the updates
on the publisher are targeted only towards specific columns, the user will
have an option to reduce network consumption by not sending the data
corresponding to new columns that do not change. Note that replica
identity values will always be sent irrespective of column filtering settings.
The column values that are not sent by the publisher will be populated
using local values on the subscriber. For insert command, non-replicated
column values will be NULL or the default.
If column names are not specified while creating or altering a publication,
all the columns are replicated as per current behaviour.

The proposal for syntax to add table with column names to publication is as
follows:
Create publication:

CREATE PUBLICATION <pub_name> [ FOR TABLE [ONLY] table_name [(colname
[,…])] | FOR ALL TABLES]

Alter publication:

ALTER PUBLICATION <pub_name> ADD TABLE [ONLY] table_name [(colname [, ..])]

Please find attached a patch that implements the above proposal.
While the patch contains basic implementation and tests, several
improvements
and sanity checks are underway. I will post an updated patch with those
changes soon.

Kindly let me know your opinion.

Thank you,

Rahila Syed