Re: Delay the variable initialization in get_rel_sync_entry

When reviewing some logical replication patches. I noticed that in

function get_rel_sync_entry() we always invoke get_rel_relispartition() 

and get_rel_relkind() at the beginning which could cause unnecessary

cache access.

---

get_rel_sync_entry(PGOutputData *data, Oid relid)

{

RelationSyncEntry *entry;

bool am_partition = get_rel_relispartition(relid);

char relkind = get_rel_relkind(relid);

---

The extra cost could sometimes be noticeable because get_rel_sync_entry is a

hot function which is executed for each change. And the 'am_partition' and

'relkind' are necessary only when we need to rebuild the RelationSyncEntry.

Here is the perf result for the case when inserted large amounts of data into a

un-published table in which case the cost is noticeable.

--12.83%--pgoutput_change

    |--11.84%--get_rel_sync_entry

    |--4.76%--get_rel_relispartition

|--4.70%--get_rel_relkind