Re:Re: BUG #18486: Is there something wrong with the calculation in ReorderBufferChangeSize()? - Mailing list pgsql-bugs

>On Thu, May 30, 2024 at 2:30 AM PG Bug reporting form
><noreply@postgresql.org> wrote:
>>
>> The following bug has been logged on the website:
>>
>> Bug reference:      18486
>> Logged by:          Xingwang Xu
>> Email address:      xu.xw2008@163.com
>> PostgreSQL version: 17beta1
>> Operating system:   CentOS7.9
>> Description:
>>
>> In the code related to logical replication, there is a function
>> ReorderBufferChangeSize(), which is used to calculate the size of a change
>> in memory.
>>
>> When looking at the ReorderBufferChangeSize() function, I saw the following
>> code：
>>
>>     case REORDER_BUFFER_CHANGE_MESSAGE:
>>         {
>>             Size        prefix_size = strlen(change->data.msg.prefix) + 1;
>>
>>             sz += prefix_size + change->data.msg.message_size +
>>                 sizeof(Size) + sizeof(Size);
>>
>>             break;
>>         }
>>
>> When calculating the change size of the message type, there are two
>> “sizeof(Size)” in the code. It is not clear why these two “sizeof(Size)” are
>> added and whether these two “sizeof(Size)” are redundant.
>>
>
>These two sizeof(Size) are added as while serializing or restoring
>message change, we explicitly serialize/restore the size of the prefix
>and the actual message. See
>ReorderBufferSerializeChange()/ReorderBufferRestoreChange().
>

Thanks for your reply.

I see in the code that the function ReorderBufferChangeSize() is used to calculate the space in memory, while ReorderBufferSerializeChange()/ReorderBufferRestoreChange() calculates the space on disk. 
Am I right in understanding this?

With Regards,
Xingwang Xu