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
Good catch. WFM. Deferring variable initialization close to its first use is
good practice.
