Re: Proposal: Conflict log history table for Logical Replication

On Wed, Dec 17, 2025 at 3:14 PM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
>
> I don’t think a user intentionally dropping information_schema and
> creating their own schema (with different definitions and tables) is a
> practical scenario. While it isn’t explicitly restricted, I don’t see
> a strong need for it. OTOH, there are scenarios where, after fixing
> issues that affect the definition of information_schema on stable
> branches, users may be asked to reload information_schema to apply the
> updated definitions. One such case can be seen in [1].
>
> Additionally, while reviewing the code, I noticed places where the
> logic does not rely solely on relid being less than
> FirstNormalObjectId. Instead, it performs name-based comparisons,
> explicitly accounting for the possibility that information_schema may
> have been dropped and reloaded. This further indicates that such
> scenarios are considered practical. See [2].
> And if such scenarios are possible, it might be worth considering
> keeping the publish behavior consistent, both before and after a
> reload of information_schema.
>
> [1]:
> https://www.postgresql.org/docs/9.1/release-9-1-2.html
>
> [2]:
> pg_upgrade has this:
> static DataTypesUsageChecks data_types_usage_checks[] =
> {
> /*
> * Look for composite types that were made during initdb *or* belong to
> * information_schema; that's important in case information_schema was
> * dropped and reloaded.
> *
> * The cutoff OID here should match the source cluster's value of
> * FirstNormalObjectId. We hardcode it rather than using that C #define
> * because, if that #define is ever changed, our own version's value is
> * NOT what to use. Eventually we may need a test on the
> source cluster's
> * version to select the correct value.
> */
> {
> .status = gettext_noop("Checking for system-defined
> composite types in user tables"),
> .report_filename = "tables_using_composite.txt",
> .base_query =
> "SELECT t.oid FROM pg_catalog.pg_type t "
> "LEFT JOIN pg_catalog.pg_namespace n ON t.typnamespace = n.oid "
> " WHERE typtype = 'c' AND (t.oid < 16384 OR nspname =
> 'information_schema')",

Yeah I agree with your theory. While the system allows users to
manually create an information_schema or place objects within it, we
are establishing that anything inside this schema will be treated as
an internal object. If a user chooses to bypass these conventions and
then finds the objects are not handled like standard user tables, it
constitutes a usage error rather than a system bug.

--
Regards,
Dilip Kumar
Google