Solr managed-schema 'for best index size and searching performance, set "index" to false'. Why?

Question

Inside the _default Solr 7.6.0 managed-schema file, it states:

'for best index size and searching performance, set "index" to false'.

After trawling through the Solr documentation I do not see how Solr can search a field if index is set to false?

I totally understand why this is the 'best size' but my question is; how would setting index to false give the best 'searching performance'?

Surely the whole point of setting index to true is to boost search performance.

Answer 1

well, it says this (in the version I had around right now):

for best index size and searching performance, set "index" to false for all general text fields, use copyField to copy them to the catchall "text" field, and use that for searching.

so you would still index that catchall field, just not all individual fields. Size and search performance would be ok, but relevance would be worse than if you index individual fields and then search on them with edismax using different boosts depending on the field importance etc.

If you don't index a field, you cannot search. You could still sort/facet if you use docvalues on the field though.