Hi,
On 2023-07-31 21:25:06 +0000, José Neves wrote:
> Ok, if I understood you correctly, I start to see where my logic is faulty. Just to make sure that I got it right,
takingthe following example again:
>
> T-1
> INSERT LSN1-1000
> UPDATE LSN2-2000
> UPDATE LSN3-3000
> COMMIT LSN4-4000
>
> T-2
> INSERT LSN1-500
> UPDATE LSN2-1500
> UPDATE LSN3-2500
> COMMIT LSN4-5500
>
> Where data will arrive in this order:
>
> INSERT LSN1-500
> INSERT LSN1-1000
> UPDATE LSN2-1500
> UPDATE LSN2-2000
> UPDATE LSN3-2500
> UPDATE LSN3-3000
> COMMIT LSN4-4000
> COMMIT LSN4-5500
No, they won't arrive in that order. They will arive as
BEGIN
INSERT LSN1-1000
UPDATE LSN2-2000
UPDATE LSN3-3000
COMMIT LSN4-4000
BEGIN
INSERT LSN1-500
UPDATE LSN2-1500
UPDATE LSN3-2500
COMMIT LSN4-5500
Because T1 committed before T2. Changes are only streamed out at commit /
prepare transaction (*). Within a transaction, they however *will* be ordered
by LSN.
(*) Unless you use streaming mode, in which case it'll all be more
complicated, as you'll also receive changes for transactions that might still
abort.
> You are saying that the LSN3-3000 will never be missing, either the entire
> connection will fail at that point, or all should be received in the
> expected order (which is different from the "numeric order" of LSNs).
I'm not quite sure what you mean with the "different from the numeric order"
bit...
> If the connection is down, upon restart, I will receive the entire T-1
> transaction again (well, all example data again).
Yes, unless you already acknowledged receipt up to LSN4-4000 and/or are only
asking for newer transactions when reconnecting.
> In addition to that, if I commit LSN4-4000, even tho that LSN has a "bigger
> numeric value" than the ones representing INSERT and UPDATE events on T-2, I
> will be receiving the entire T-2 transaction again, as the LSN4-5500 is
> still uncommitted.
I don't quite know what you mean with "commit LSN4-4000" here.
> This makes sense to me, but just to be extra clear, I will never receive a
> transaction commit before receiving all other events for that transaction.
Correct.
Greetings,
Andres Freund