Re: Support logical replication of DDLs

Hello,

Thanks for the feedback.

> I have been following this patch for a long time.
> Recently, I started to try to test it. I found several bugs
> here and want to give you feedback.
>
> 1. CREATE TABLE LIKE
> I found that this case may be repication incorrectly.
> You can run the following SQL statement:
> ```
> CREATE TABLE ctlt1 (a text CHECK (length(a) > 2) PRIMARY KEY, b text);
> ALTER TABLE ctlt1 ALTER COLUMN a SET STORAGE MAIN;
> ALTER TABLE ctlt1 ALTER COLUMN b SET STORAGE EXTERNAL;
> CREATE TABLE ctlt1_like (LIKE ctlt1 INCLUDING ALL);
> ```
> The ctlt1_like table will not be able to correct the replication.
> I think this is because create table like statement is captured by
> the event trigger to a create table statement and multiple alter table statements.
> There are some overlaps between them, and an error is reported when downstream replication occurs.

I looked into this case. The root cause is the statement

CREATE TABLE ctlt1_like (LIKE ctlt1 INCLUDING ALL);

is executed internally using 3 DDLs:
1. CREATE TABLE ctlt1_like (LIKE ctlt1 INCLUDING ALL); --The top level command
2. ALTER TABLE ctlt1_like ADD CONSTRAINT ctlt1_a_check CHECK
(length(a) > 2); --The first subcommand
3. CREATE UNIQUE INDEX ctlt1_like_pkey on ctlt1_like (a); --The second
subcommand that creates the primary key index

All three commands are captured by the event trigger. The first and
second command ends up getting deparsed, WAL-logged and
replayed on the subscriber. The replay of the ALTER TABLE command
causes a duplicate constraint error. The problem is that
while subcommands are captured by event triggers by default, they
don't need to be deparsed and WAL-logged for DDL replication.
To do that we can pass the isCompleteQuery variable in
ProcessUtilitySlow to EventTriggerCollectSimpleCommand() and
EventTriggerAlterTableEnd() and make this information available in
CollectedCommand so that any subcommands can be skipped.

Thoughts?
Zheng