On Wed, Aug 17, 2022 at 12:34 PM Peter Smith <smithpb2...@gmail.com> wrote: > > On Wed, Aug 17, 2022 at 4:33 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > > > On Wed, Aug 17, 2022 at 8:48 AM houzj.f...@fujitsu.com > > <houzj.f...@fujitsu.com> wrote: > > > > > > On Tuesday, August 2, 2022 8:00 PM Amit Kapila <amit.kapil...@gmail.com> > > > wrote: > > > > On Tue, Jul 26, 2022 at 9:07 AM Amit Kapila <amit.kapil...@gmail.com> > > > > wrote: > > > > > > Thanks for the summary. > > > > > > I think it's fine to make the user use the copy_data option more > > > carefully to > > > prevent duplicate copies by reporting an ERROR. > > > > > > But I also have similar concern with Sawada-san as it's possible for user > > > to > > > receive an ERROR in some unexpected cases. > > > > > > For example I want to build bi-directional setup between two nodes: > > > > > > Node A: TABLE test (has actual data) > > > Node B: TABLE test (empty) > > > > > > Step 1: > > > CREATE PUBLICATION on both Node A and B. > > > > > > Step 2: > > > CREATE SUBSCRIPTION on Node A with (copy_data = on) > > > -- this is fine as there is no data on Node B > > > > > > Step 3: > > > CREATE SUBSCRIPTION on Node B with (copy_data = on) > > > -- this should be fine as user needs to copy data from Node A to Node B, > > > -- but we still report an error for this case. > > > > > > It looks a bit strict to report an ERROR in this case and it seems not > > > easy to > > > avoid this. So, personally, I think it might be better to document the > > > correct > > > steps to build the bi-directional replication and probably also docuemnt > > > the > > > steps to recover if user accidently did duplicate initial copy if not > > > documented yet. > > > > > > In addition, we could also LOG some additional information about the > > > ORIGIN and > > > initial copy which might help user to analyze if needed. > > > > > > > But why LOG instead of WARNING? I feel in this case there is a chance > > of inconsistent data so a WARNING like "publication "pub1" could have > > data from multiple origins" can be given when the user has specified > > options: "copy_data = on, origin = NONE" while creating a > > subscription. We give a WARNING during subscription creation when the > > corresponding publication doesn't exist, eg. > > > > postgres=# create subscription sub1 connection 'dbname = postgres' > > publication pub1; > > WARNING: publication "pub1" does not exist in the publisher > > > > Then, we can explain in docs how users can avoid data inconsistencies > > while setting up replication. > > > > I was wondering if this copy/origin case really should be a NOTICE. >
We usually give NOTICE for some sort of additional implicit information, e.g., when we create a slot during CREATE SUBSCRIPTION command: "NOTICE: created replication slot "sub1" on publisher". IMO, this is likely to be a problem of data inconsistency so I think here we can choose between WARNING and LOG. I prefer WARNING but okay with LOG as well if others feel so. I think we can change this later as well if required. We do have an option to not do anything and just document it but I feel it is better to give user some indication of problem here because not everyone reads each update of documentation. Jonathan, Sawada-San, Hou-San, and others, what do you think is the best way to move forward here? -- With Regards, Amit Kapila.
