Thread

Re: Proposal: Conflict log history table for Logical Replication

Dilip Kumar <dilipbalaut@gmail.com> — 2025-12-14T15:46:30Z

On Sun, Dec 14, 2025 at 3:51 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
>
> On Fri, Dec 12, 2025 at 3:04 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > On Thu, Dec 11, 2025 at 7:49 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
> > >
> > > I was considering the interdependence between the subscription and the
> > > conflict log table (CLT). IMHO, it would be logical to establish the
> > > subscription as dependent on the CLT. This way, if someone attempts to
> > > drop the CLT, the system would recognize the dependency of the
> > > subscription and prevent the drop unless the subscription is removed
> > > first or the CASCADE option is used.
> > >
> > > However, while investigating this, I encountered an error [1] stating
> > > that global objects are not supported in this context. This indicates
> > > that global objects cannot be made dependent on local objects.
> > >
> >
> > What we need here is an equivalent of DEPENDENCY_INTERNAL for database
> > objects. For example, consider following case:
> > postgres=# create table t1(c1 int primary key);
> > CREATE TABLE
> > postgres=# \d+ t1
> >                                            Table "public.t1"
> >  Column |  Type   | Collation | Nullable | Default | Storage |
> > Compression | Stats target | Description
> > --------+---------+-----------+----------+---------+---------+-------------+--------------+-------------
> >  c1     | integer |           | not null |         | plain   |
> >     |              |
> > Indexes:
> >     "t1_pkey" PRIMARY KEY, btree (c1)
> > Publications:
> >     "pub1"
> > Not-null constraints:
> >     "t1_c1_not_null" NOT NULL "c1"
> > Access method: heap
> > postgres=# drop index t1_pkey;
> > ERROR:  cannot drop index t1_pkey because constraint t1_pkey on table
> > t1 requires it
> > HINT:  You can drop constraint t1_pkey on table t1 instead.
> >
> > Here, the PK index is created as part for CREATE TABLE operation and
> > pk_index is not allowed to be dropped independently.
> >
> > > Although making an object dependent on global/shared objects is
> > > possible for certain types of shared objects [2], this is not our main
> > > objective.
> > >
> >
> > As per my understanding from the above example, we need something like
> > that only for shared object subscription and (internally created)
> > table.
>
> Yeah that seems to be exactly what we want, so I tried doing that by
> recording DEPENDENCY_INTERNAL dependency of CLT on subscription[1] and
> it is behaving as we want[2].  And while dropping the subscription or
> altering CLT we can delete internal dependency so that CLT get dropped
> automatically[3]
>
> I will send an updated patch after testing a few more scenarios and
> fixing other pending issues.
>
> [1]
> +       ObjectAddressSet(myself, RelationRelationId, relid);
> +       ObjectAddressSet(subaddr, SubscriptionRelationId, subid);
> +       recordDependencyOn(&myself, &subaddr, DEPENDENCY_INTERNAL);
>
>
> [2]
> postgres[670778]=# DROP TABLE myschema.conflict_log_history2;
> ERROR:  2BP01: cannot drop table myschema.conflict_log_history2
> because subscription sub requires it
> HINT:  You can drop subscription sub instead.
> LOCATION:  findDependentObjects, dependency.c:788
> postgres[670778]=#
>
> [3]
> ObjectAddressSet(object, SubscriptionRelationId, subid);
> performDeletion(&object, DROP_CASCADE
>                            PERFORM_DELETION_INTERNAL |
>                            PERFORM_DELETION_SKIP_ORIGINAL);
>
>

Here is the patch which implements the dependency and fixes other
comments from Shveta.

-- 
Regards,
Dilip Kumar
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