How can I ensure to have an index on a custom field and make it Primary? My Lookup field is a custom field, will that be as efficient as any other custom field I create or we have to someway create an index on this field?
You can't manually index a field. If it's eligible for lookup then it's as efficient as any other.
What makes a custom field eligible for lookup?
FYI - on my Sandbox environment I am able to send the lead data using this custom field as lookup.
Any custom String, Email, or Integer field is eligible AFAIK. Note it would never be the primary key anyway, you could be thinking about a unique key (which it's not) but in any case the indexing isn't under user control.
Ok, so just want to be clear, since right now I am only pushing some test data, using a custom field of data type integer as lookup field. It seems to be working fine. But will it be a potential issue when volumes of data will be pushed later, and if there is no indexing or uniqueness on this key, it might slow down or cause any issue?
If there are chances of any issue, what would be recommended solution?
The implication is that there's a covered index for each available custom field + the lead ID. Ergo, there may be 2 lookups necessary, but both are indexed.
I did not get the response clearly. Do you mean I should not worry about indexing or performance, it will be good?