This bug is created as a clone of upstream ticket:
https://fedorahosted.org/389/ticket/47504

With very large databases, some queries go through a lot of work to build huge ID lists for filter components with many matching IDs.  For example, a search for (&(objectclass=inetorgperson)(uid=foo)) may build a huge idlist for objectclass=inetorgperson only to throw it away to intersect it with uid=foo.  In these cases, it would be useful to be able to tell the indexing code to use a different idlistscanlimit for certain indexes, or use no idlist at all.  In the above case, it would be useful to tell the indexing code to skip building an idlist for objectclass=inetorgperson, but still use the default idlistscanlimit for other objectclass searches (e.g. objectclass=groupOfNames).

This would also help in https://fedorahosted.org/389/ticket/47474 - if there are several million IDs for each of the objectclass= filter components, being able to skip id list generation for the objectclass values would make that query very fast.

We can't reuse nsslapd-idlistscanlimit, so perhaps a new attribute

dn: cn=attrname,cn=index,...
objectclass: nsIndex
nsIndexIDSize: NNNN[:type][:eqvalue:eqvalue:...]

Where NNNN is the max ID list size (or 0 for no list at all)
type is the type of index (sub, pres, eq)
eqvalue are for equality indexes - these are the values to which the max ID list size applies

So in the case of ticket/47474, something like

dn: cn=objectclass,...
objectclass: nsIndex
nsIndexType: eq
nsIndexIDSize: 0:eq:organizationalPerson:inetOrgPerson:organization:organizationalUnit:groupOf
Names:groupOfUniqueNames:group

Would effectively disable id list generation for the objectclass values listed.

Note that this will apply to _all_ queries for any of the objectclass values, not just their use in conjunction with this particular search filter.