On Tue, Aug 10, 2021 at 8:08 PM Alvaro Herrera <alvhe...@alvh.no-ip.org> wrote: > > On 2021-Jul-30, Amit Kapila wrote: > > Reading Dilip's last posted patch that day, I had some reservations > about the API of ExtractReplicaIdentity. The new argument makes for a > very strange to explain behavior "return the key values if they are > unchanged, *or* if they are toasted" ... ??? >
I think we can say it as "Return the key values if they are changed *or* if they are toasted". Currently, we have an exception for Deletes where the caller always passed key_changed as true, so maybe we can have a similar exception when the tuple has toasted values. Can we think of changing the flag to "key_required" instead of "key_changed" and let the caller identify and set its value? For Deletes, it will work the same but for Updates, the caller needs to compute it by checking if any of the key columns are modified or has a toast value. We can try to see if the caller can identify it cheaply along with determining the modified_attrs as at that time we will anyway check replica key attrs. Currently, in proposed patch first, we check that the tuple has any toast values and then it deforms and forms the new key tuple. After that, it checks if the key has any toast values and then only decides to return the tuple. If as described in the previous paragraph, we can cheaply identify whether the key has toasted values, then we can avoid deform/form cost in some cases. Also, I think we need to change the Replica Identity description in the docs[1]. [1] - https://www.postgresql.org/docs/devel/sql-altertable.html -- With Regards, Amit Kapila.
