Cross-extension pg_extension_config_dump and data duplicates

[yrashk]

Here's an interesting problem. Let's suppose we have two extensions, A and B.

A has a table a_config. The rows are marked with bundled column to make sure pg_extension_config_dump doesn't capture data provided by the etension itself. All good so far.

A defines a function f() that effectively adds new records to a_config

Now, extension B depends A, and uses A.f() to add new records. However, they are not considered bundled anymore – unless we do something explicit about it.

The problem is that now when pg_dump will attempt to restore data after getting A installed, it'll send duplicates to be inserted.

So far, the only solution I have is to introduce a setting that opting in extensions would have to set – something to the tune of extension.create_in_progress and bundled should look into it to determine if the record should be considered bundled.

If this works well enough, perhaps this can be proposed upstream to make Postgres set such a variable when extensions are being installed. Another way to do this would be to expose creating_extension as a function https://doxygen.postgresql.org/extension_8c.html#a5f774b51db47b6cae5dbf63f6035cbcf

Thoughts?

[yrashk]

Proposed a patch upstream: https://www.postgresql.org/message-id/CAG%3DVW17kAweKGwqtVU8vn71uRCOS9yxnyEnoa%3D-3sAuyZt5O6g%40mail.gmail.com