Optimize search3, by removing OFFSET when paginating (#2655)

* Optimize pagination, removing offset

* For search, don't add `where` clause for empty queries

* Revert "Replace `COUNT(DISTINCT primary_key)` with `COUNT(*)`"

Genres are required as part of the count queries, so filter by genres work

* Optimize search3 query, using order by id if it is a "" query.

Also fix the optimizePagination query logic

* Allow offset optimizer threshold to be configured

persistence/sql_search.go

@@ -5,6 +5,7 @@ import (
 
 	. "github.com/Masterminds/squirrel"
 	"github.com/navidrome/navidrome/conf"
+	"github.com/navidrome/navidrome/model"
 	"github.com/navidrome/navidrome/utils"
 )
 
@@ -21,21 +22,31 @@ func (r sqlRepository) doSearch(q string, offset, size int, results interface{},
 	}
 
 	sq := r.newSelectWithAnnotation(r.tableName + ".id").Columns("*")
-	sq = sq.Limit(uint64(size)).Offset(uint64(offset))
-	if len(orderBys) > 0 {
-		sq = sq.OrderBy(orderBys...)
+	filter := fullTextExpr(q)
+	if filter != nil {
+		sq = sq.Where(filter)
+		if len(orderBys) > 0 {
+			sq = sq.OrderBy(orderBys...)
+		}
+	} else {
+		// If the filter is empty, we sort by id.
+		// This is to speed up the results of `search3?query=""`, for OpenSubsonic
+		sq = sq.OrderBy("id")
 	}
-	sq = sq.Where(fullTextExpr(q))
-	err := r.queryAll(sq, results)
+	sq = sq.Limit(uint64(size)).Offset(uint64(offset))
+	err := r.queryAll(sq, results, model.QueryOptions{Offset: offset})
 	return err
 }
 
 func fullTextExpr(value string) Sqlizer {
+	q := utils.SanitizeStrings(value)
+	if q == "" {
+		return nil
+	}
 	var sep string
 	if !conf.Server.SearchFullString {
 		sep = " "
 	}
-	q := utils.SanitizeStrings(value)
 	parts := strings.Split(q, " ")
 	filters := And{}
 	for _, part := range parts {