SERVER-9212 SERVER-8791 kill newCursor and suitability, centralize latter

1 files changed, 42 insertions, 0 deletions

diff --git a/src/mongo/db/index_selection.h b/src/mongo/db/index_selection.h
new file mode 100644
index 00000000000..e64978f638e
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+++ b/src/mongo/db/index_selection.h
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+/**
+*    Copyright (C) 2013 10gen Inc.
+*
+*    This program is free software: you can redistribute it and/or  modify
+*    it under the terms of the GNU Affero General Public License, version 3,
+*    as published by the Free Software Foundation.
+*
+*    This program is distributed in the hope that it will be useful,
+*    but WITHOUT ANY WARRANTY; without even the implied warranty of
+*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*    GNU Affero General Public License for more details.
+*
+*    You should have received a copy of the GNU Affero General Public License
+*    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#pragma once
+
+#include "mongo/db/indexkey.h"  // for IndexSuitability
+
+namespace mongo {
+
+    class BSONObj;
+    class FieldRangeSet;
+
+    /**
+     * This class is part of query optimization.  For a given index (as uniquely described by
+     * keyPattern) and a given query (queryConstraints) and given sort order (order), return how
+     * "suitable" the index is for the query + sort.
+     *
+     * USELESS indices are never used.
+     * HELPFUL indices are explored and compared to other HELPFUL indices.
+     * OPTIMAL indices short-circuit the search process and are always used.
+     */
+    class IndexSelection {
+    public:
+        static IndexSuitability isSuitableFor(const BSONObj& keyPattern,
+                                              const FieldRangeSet& queryConstraints,
+                                              const BSONObj& order);
+    };
+
+}  // namespace mongo