Sybase IQ Tiered HG Indexes Recommendation

Bonjour,

we are in the process of upgrading our IQ 15.4 database. We have had some performance gain by simply upgrading and then by rebuilding FP indexes into NBIT.

We have also had substantial gain in migrating HG indexes into TIERED HG Indexes.

We have recently read that SAP does NOT recommend that we tier all HG indexes and I was wondering why such a recommendation?

What are the drawbacks of having HG Tiered index?

Why not tier every HG indexes in the database?

Thanks