[LUCENE-2483] When loading FieldCache terms index, make terms data optional

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Fix Version/s: 4.9, 6.0
• Component/s: core/search
• Lucene Fields: New
• Assignee: Unassigned
• Reporter: Michael McCandless
• Created: 28/May/10 20:17
• Updated: 28/Aug/22 12:27

Description

Spinoff of LUCENE-2380.

Now, when you load the terms index (FC.getTermsIndex), it loads two
arrays, ord (maps docID -> ord) and lookup (maps ord -> term).

But sometimes you don't need the lookup map (and, it's often very
costly in RAM usage, much moreso than the ord map).

EG if your index is a single segment, and your app doesn't need the
values (LUCENE-2335).

Or, if you use a sort comparator that resolves ord -> term and v/v (eg
using terms dict).

So we should make it optional...

Also, similarly, we could merge getTerms/getTermsIndex. It's
dangerous today if you load terms and then termsIndex because you're
wasting tons of RAM; it'd be nicer if we could have a single cache
entry that'd "upgrade" itself to be an index (have the ords). This
single entry could then serve ords, ords+terms, or just terms.