Re: row filtering for logical replication

On 7/14/21 4:52 PM, Alvaro Herrera wrote:
> On 2021-Jul-14, Tomas Vondra wrote:
> 
>> The way I'm thinking about this is that for INSERT and DELETE it's clear
>> which row version should be used (because there's just one). And for UPDATE
>> we could see that as DELETE + INSERT, and apply the same rule to each
>> action.
>>
>> On the other hand, I can imagine cases where it'd be useful to send the
>> UPDATE when the old row matches the condition and new row does not.
> 
> In any case, it seems to me that the condition expression should be
> scanned to see which columns are used in Vars (pull_varattnos?), and
> verify if those columns are in the REPLICA IDENTITY; and if they are
> not, raise an error.  Most of the time the REPLICA IDENTITY is going to
> be the primary key; but if the user wants to use other columns in the
> expression, we can HINT that they can set REPLICA IDENTITY FULL.
> 

Yeah, but AFAIK that's needed only when replicating DELETEs, so perhaps 
we could ignore this for subscriptions without DELETE.

The other question is when to check/enforce this. I guess we'll have to 
do that during decoding, not just when the publication is being created, 
because the user can do ALTER TABLE later.


regards

-- 
Tomas Vondra
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