[LUCENE-2335] optimization: when sorting by field, if index has one segment and field values are not needed, do not load String[] into field cache

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Fix Version/s: 4.9, 6.0
• Component/s: core/search
• Labels: gsoc2014
• Lucene Fields: New
• Assignee: Unassigned
• Reporter: Michael McCandless
• Created: 19/Mar/10 22:58
• Updated: 28/Aug/22 12:22

Description

Spinoff from java-dev thread "Sorting with little memory: A suggestion", started by Toke Eskildsen.

When sorting by SortField.STRING we currently ask FieldCache for a StringIndex on that field.

This can consumes tons of RAM, when the values are mostly unique (eg a title field), as it populates both int[] ords as well as String[] values.

But, if the index is only one segment, and the search sets fillFields=false, we don't need the String[] values, just the int[] ords. If the app needs to show the fields it can pull them (for the 1 page) from stored fields.

This can be a potent optimization – alot of RAM saved – for optimized indexes.

When fixing this we must take care to share the int[] ords if some queries do fillFields=true and some =false... ie, FieldCache will be called twice and it should share the int[] ords across those invocations.