Re: Wrong comment for ReplicationSlotCreate

> On Jan 2, 2026, at 00:31, Daniil Davydov <3danissimo@gmail.com> wrote:
>
> Hi,
>
> On Wed, Dec 31, 2025 at 9:32 AM Chao Li <li.evan.chao@gmail.com> wrote:
>>
>> You’re right that during CREATE_REPLICATION_SLOT, SnapBuildFindSnapshot() ensures we don’t miss PREPARE records for
preparedtransactions that exist at creation time. 
>>
>> 1462aad2e introduced support for altering logical replication slot options, including two_phase, after the slot has
beencreated. The commit comment says: 
>> ```
>>    Changing the 'two_phase' option for a subscription from 'true' to 'false'
>>    is permitted only when there are no pending prepared transactions
>>    corresponding to that subscription. Otherwise, the changes of already
>>    prepared transactions can be replicated again along with their corresponding
>>    commit leading to duplicate data or errors.
>> ```
>>
>> true->false is not allowed, however false->true is permitted. So, I think the old comment is still possible today:
>> ```
>> *     Note that enabling this option after decoding has already advanced
>> *     may result in missing PREPARE records for transactions that were
>> *     prepared before the option was enabled.
>> ```
>>
>
> Hm, I still can't understand why the comment that you provided is correct.
>
> How can we "miss PREPARE records" if slot creation requires all  prepared
> transactions to finish? The commit message says about risks during the
> change of the parameter "on the fly". But we are dealing with slot creation.
>
> --
> Best regards,
> Daniil Davydov

No problem, maybe I am wrong. Then please ignore my comment and wait for other review comments.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/