On Thu, Aug 21, 2025 at 10:53 AM Hayato Kuroda (Fujitsu)
<kuroda.hayato@fujitsu.com> wrote:
>
> > I have concerns about the performance implications of iterating
> > through all entries in the caches within
> > maybe_cleanup_rel_sync_cache(). If the cache contains numerous
> > entries, this iteration could potentially cause the walsender to
> > stall. If we use a larger number NINVALIDATION_THRESHOLD, we can
> > reduce the number of times we need sequential scans on the hash table
> > but it would in turn need to free more entries (probably we can have a
> > cap of the number of entries we can free in one cycle?).
>
> Exactly.
>
So, at least we can try some tests before completely giving up on this idea.
> > An alternative approach would be to implement a dedicated list (such
> > as dclist) specifically for tracking invalidated entries. Entries
> > would be removed from this list when they are reused. We could then
> > implement a threshold-based cleanup mechanism where invalidated
> > entries are freed once the list exceeds a predetermined size. While
> > this approach would minimize the overhead of freeing invalidated
> > entries, it would incur some additional cost for maintaining the list.
>
> Firstly I also considered but did not choose because of the code complexity.
> After considering more, it is not so difficult, PSA new file.
>
The other idea I was thinking of is if somehow we can decode the DROP
TABLE WAL record, say delete of relid from pg_class then we can use
that to remove the corresponding entry from RelationSyncCache.
--
With Regards,
Amit Kapila.
