[IMPROVED] Single subject in FilterSubjects field

[MauriceVanVeen]

We would populate o.filters even if FilterSubjects has a single entry, which would make us use LoadNextMsgMulti versus LoadNextMsg. o.updateConfig would already correctly populate o.subjf and o.filters in the same way.

Resolves #7852

Signed-off-by: Maurice van Veen github@mauricevanveen.com

[neilalexander]

Would it better to gate on o.filters.Count() at the callsite of LoadNextMsg/LoadNextMsgMulti instead? That way we get the same optimisation for both SubjectFilter = "foo" and SubjectFilters = []string{"foo"}.

[MauriceVanVeen]

Would it better to gate on o.filters.Count() at the callsite of LoadNextMsg/LoadNextMsgMulti instead? That way we get the same optimisation for both SubjectFilter = "foo" and SubjectFilters = []string{"foo"}.

In essence setting o.filters to a sublist is what makes us use LoadNextMsgMulti, as it should only be populated if there are multiple filters. It was a bug that we did do this properly in o.updateConfig but not when creating the consumer initially.

All callsites of LoadNextMsg/Multi (o.getNextMsg and o.checkStateForInterestStream), already use nil-checks on o.filters and fallback to o.subjf. So I'm thinking the current approach is already both consistent with o.updateConfig and effective at not using LoadNextMsgMulti when there's only a single subject in FilterSubjects.

[neilalexander]

Should this be <= 1?

[MauriceVanVeen]

Done, also changed the else if to just an else.

[neilalexander]

LGTM!