Re: Large expressions in indexes can't be stored (non-TOASTable)

On Tue, Apr 22, 2025 at 05:17:17PM +0530, Nisha Moond wrote:
> Thanks for the patch! I tested it for functionality and here are a few comments:

Thank you for reviewing.

> 1) While testing, I noticed an unexpected behavior with the new 512
> byte length restriction in place. Since there´s no explicit
> restriction on the column roname´s type, it´s possible to insert an
> origin name exceeding 512 bytes. For instance, can use the COPY
> command -- similar to how pg_dump might dump and restore catalog
> tables.
>
> For example:
> postgres=# COPY pg_catalog.pg_replication_origin (roident, roname) FROM stdin;
> Enter data to be copied followed by a newline.
> End with a backslash and a period on a line by itself, or an EOF signal.
> >> 44 regress_aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa... [>512 bytes string]
> >> \.
> COPY 1
>
> Once inserted, I was able to use the pg_replication_origin_xxx
> functions with this origin name without any errors.
> Not sure how common pg_dump/restore of catalog tables is in real
> systems, but should we still consider if this behavior is acceptable?

I'm personally not too worried about this. The limit is primarily there to
provide a nicer ERROR than "row is too big", which AFAICT is the worst-case
scenario if you go to the trouble of setting allow_system_table_mods and
modifying shared catalogs directly.

> 5) As Euler pointed out, logical replication already has a built-in
> restriction for internally assigned origin names, limiting them to
> NAMEDATALEN. Given that, only the SQL function
> pg_replication_origin_create() is capable of creating longer origin
> names. Would it make sense to consider moving the check into
> pg_replication_origin_create() itself, since it seems redundant for
> all other callers?
> That said, if there's a possibility of future callers needing this
> restriction at a lower level, it may be reasonable to leave it as is.

pg_replication_origin_create() might be a better place. After all, that's
where we're enforcing the name doesn't start with "pg_" and, for testing,
_does_ start with "regress_". Plus, it seems highly unlikely that any
other callers of replorigin_create() will ever provide names longer than
512 bytes.

--
nathan