Re: Delay the variable initialization in get_rel_sync_entry

On Wed, Dec 22, 2021, at 10:11 AM, houzj(dot)fnst(at)fujitsu(dot)com wrote:
> 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.

--
Euler Taveira
EDB https://www.enterprisedb.com/