Re:Re: Is there any plan to support online schem change in postgresql?

But, as follow, if txn1 not commit (just like long term readonly txn), it will block txn2's ddl job, why alt add/drop column can not concurrently with read only access?

txn1： long term txn not commit access t1.
txn2 waiting txn1 to commit or abort.

txn3 wait txn2...

At 2022-10-11 18:05:01, "hubert depesz lubaczewski" <depesz(at)depesz(dot)com> wrote:
>On Tue, Oct 11, 2022 at 05:43:03PM +0800, jiye wrote:
>> As we know postgres using high level lock when do alter table or other ddl commands,
>> It will block any dml operation, while it also will block by long term dml operation.
>
>Most of the things can be already done in non-blocking (or almost
>non-blocking way) if you just do it in a way that takes concurrency into
>account.
>
>Specifically - I have no problem adding/deleting columns.
>
>Best regards,
>
>depesz