What are a_ref indices?

[giles_lewis]

When I look at the indices on my tables, I see a bunch of indices on fields with names like a_ref_1, a_ref_2.   What are these indices?

[VarunArulmani]

you may refer below link

How does index creation helps improving performance?

[giles_lewis]

My question is not about how indices improve performance.   My question is: What fields are being indexed by these indices?

[Vladimir Cheres]

I have the same question. Have you found some useful information about this topic?