Hi,
In <CAKFQuwaRDXANaL+QcT6LZRAem4rwkSwv9v+viv_mcR+Rex3quA@mail.gmail.com>
"Re: Make COPY format extendable: Extract COPY TO format implementations" on Sat, 3 May 2025 22:27:36 -0700,
"David G. Johnston" <david.g.johnston@gmail.com> wrote:
> In any case, I’m doubtful either of us can make a convincing enough
> argument to sway the other fully. Both options are plausible, IMO. Others
> need to chime in.
I may misunderstand but here is the current summary, right?
Proposed approaches to register custom COPY formats:
a. Create a function that has the same name of custom COPY
format
b. Call a register function from _PG_init()
FYI: I proposed c. approach that uses a. but it always
requires schema name for format name in other e-mail.
Users can register the same format name:
a. Yes
* Users can distinct the same format name by schema name
* If format name doesn't have schema name, the used
format depends on search_path
* Pros:
* Using schema for it is consistent with other
PostgreSQL mechanisms
* Custom format never conflict with built-in
format. For example, an extension register "xml" and
PostgreSQL adds "xml" later, they are never
conflicted because PostgreSQL's "xml" is registered
to pg_catalog.
* Cons: Different format may be used with the same
input. For example, "jsonlines" may choose
"jsonlines" implemented by extension X or implemented
by extension Y when search_path is different.
b. No
* Users can use "${schema}.${name}" for format name
that mimics PostgreSQL's builtin schema (but it's just
a string)
Built-in formats (text/csv/binary) should be able to
overwritten by extensions:
a. (The current patch is no but David's answer is) Yes
* Pros: Users can use drop-in replacement faster
implementation without changing input
* Cons: Users may overwrite them accidentally.
It may break pg_dump result.
(This is called as "backward incompatibility.")
b. No
Are there any missing or wrong items? If we can summarize
the current discussion here correctly, others will be able
to chime in this discussion. (At least I can do it.)
Thanks,
--
kou
