On Thu, 30 May 2024 at 06:21, Peter Smith <smithpb2...@gmail.com> wrote: > > On Wed, May 29, 2024 at 8:04 PM vignesh C <vignes...@gmail.com> wrote: > > > > On Wed, 22 May 2024 at 14:26, Peter Smith <smithpb2...@gmail.com> wrote: > > > > > > On Tue, May 21, 2024 at 8:40 PM PG Doc comments form > > > <nore...@postgresql.org> wrote: > > > > > > > > The following documentation comment has been logged on the website: > > > > > > > > Page: > > > > https://www.postgresql.org/docs/16/logical-replication-col-lists.html > > > > Description: > > > > > > > > The documentation on this page mentions: > > > > > > > > "If no column list is specified, any columns added later are > > > > automatically > > > > replicated." > > > > > > > > It feels ambiguous what this could mean. Does it mean: > > > > > > > > 1/ That if you alter the table on the publisher and add a new column, it > > > > will be replicated > > > > > > > > 2/ If you add a column list later and add a column to it, it will be > > > > replicated > > > > > > > > In both cases, does the subscriber automatically create this column if > > > > it > > > > wasn't there before? > > > > > > No, the subscriber will not automatically create the column. That is > > > already clearly said at the top of the same page you linked "The table > > > on the subscriber side must have at least all the columns that are > > > published." > > > > > > All that "If no column list..." paragraph was trying to say is: > > > > > > CREATE PUBLICATION pub FOR TABLE T; > > > > > > is not quite the same as: > > > > > > CREATE PUBLICATION pub FOR TABLE T(a,b,c); > > > > > > The difference is, in the 1st case if you then ALTER the TABLE T to > > > have a new column 'd' then that will automatically start replicating > > > the 'd' data without having to do anything to either the PUBLICATION > > > or the SUBSCRIPTION. Of course, if TABLE T at the subscriber side does > > > not have a column 'd' then you'll get an error because your subscriber > > > table needs to have *at least* all the replicated columns. (I > > > demonstrate this error below) > > > > > > Whereas in the 2nd case, even though you ALTER'ed the TABLE T to have > > > a new column 'd' then that won't be replicated because 'd' was not > > > named in the PUBLICATION's column list. > > > > > > ~~~~ > > > > > > Here's an example where you can see this in action > > > > > > Here is an example of the 1st case -- it shows 'd' is automatically > > > replicated and also shows the subscriber-side error caused by the > > > missing column: > > > > > > test_pub=# CREATE TABLE T(a int,b int, c int); > > > test_pub=# CREATE PUBLICATION pub FOR TABLE T; > > > > > > test_sub=# CREATE TABLE T(a int,b int, c int); > > > test_sub=# CREATE SUBSCRIPTION sub CONNECTION 'dbname=test_pub' > > > PUBLICATION pub; > > > > > > See the replication happening > > > test_pub=# INSERT INTO T VALUES (1,2,3); > > > test_sub=# SELECT * FROM t; > > > a | b | c > > > ---+---+--- > > > 1 | 2 | 3 > > > (1 row) > > > > > > Now alter the publisher table T and insert some new data > > > test_pub=# ALTER TABLE T ADD COLUMN d int; > > > test_pub=# INSERT INTO T VALUES (5,6,7,8); > > > > > > This will cause subscription errors like: > > > 2024-05-22 11:53:19.098 AEST [16226] ERROR: logical replication > > > target relation "public.t" is missing replicated column: "d" > > > > > > ~~~~ > > > > > > I think the following small change will remove any ambiguity: > > > > > > BEFORE > > > If no column list is specified, any columns added later are > > > automatically replicated. > > > > > > SUGGESTION > > > If no column list is specified, any columns added to the table later > > > are automatically replicated. > > > > > > ~~ > > > > > > I attached a small patch to make the above change. > > > > A small recommendation: > > It would enhance clarity to include a line break following "If no > > column list is specified, any columns added to the table later are": > > - If no column list is specified, any columns added later are > > automatically > > + If no column list is specified, any columns added to the table > > later are automatically > > replicated. This means that having a column list which names all columns > > Hi Vignesh, > > IIUC you're saying my v1 patch *content* and rendering is OK, but you > only wanted the SGML text to have better wrapping for < 80 chars > lines. So I have attached a patch v2 with improved wrapping. If you > meant something different then please explain.
Yes, that is what I meant and the updated patch looks good. Regards, Vignesh
