SERVER-10026 push access method name into index descriptor, pay attention to it in planning

1 files changed, 31 insertions, 14 deletions

diff --git a/src/mongo/db/index_names.h b/src/mongo/db/index_names.h
index 03f7786c879..fd7af42675b 100644
--- a/src/mongo/db/index_names.h
+++ b/src/mongo/db/index_names.h
@@ -37,6 +37,26 @@ namespace mongo {
     class BSONObj;
 
     /**
+     * We need to know what 'type' an index is in order to plan correctly.  We can't entirely rely
+     * on the key pattern to tell us what kind of index we have.
+     *
+     * An example of the Bad Thing That We Must Avoid:
+     * 1. Create a 2dsphere index in 2.4, insert some docs.
+     * 2. Downgrade to 2.2.  Insert some more docs into the collection w/the 2dsphere
+     *    index.  2.2 treats the index as a normal btree index and creates keys accordingly.
+     * 3. Using the 2dsphere index in 2.4 gives wrong results or assert-fails or crashes as
+     *    the data isn't what we expect.
+     */
+    enum IndexType {
+        INDEX_BTREE,
+        INDEX_2D,
+        INDEX_HAYSTACK,
+        INDEX_2DSPHERE,
+        INDEX_TEXT,
+        INDEX_HASHED,
+    };
+
+    /**
      * We use the string representation of index names all over the place, so we declare them all
      * once here.
      */
@@ -47,18 +67,14 @@ namespace mongo {
         static const string GEO_2DSPHERE;
         static const string TEXT;
         static const string HASHED;
+        static const string BTREE;
 
         /**
          * True if is a regular (non-plugin) index or uses a plugin that existed before 2.4.
          * These plugins are grandfathered in and allowed to exist in DBs with
          * PDFILE_MINOR_VERSION_22_AND_OLDER
          */
-        static bool existedBefore24(const string& name) {
-            return name.empty()
-                || name == IndexNames::GEO_2D
-                || name == IndexNames::GEO_HAYSTACK
-                || name == IndexNames::HASHED;
-        }
+        static bool existedBefore24(const string& name);
 
         /**
          * Return the first string value in the provided object.  For an index key pattern,
@@ -66,14 +82,15 @@ namespace mongo {
          */
         static string findPluginName(const BSONObj& keyPattern);
 
-        static bool isKnownName(const string& name) {
-            return name.empty()
-                   || name == IndexNames::GEO_2D
-                   || name == IndexNames::GEO_2DSPHERE
-                   || name == IndexNames::GEO_HAYSTACK
-                   || name == IndexNames::TEXT
-                   || name == IndexNames::HASHED;
-        }
+        /**
+         * Is the provided access method name one we recognize?
+         */
+        static bool isKnownName(const string& name);
+
+        /**
+         * Convert an index name to an IndexType.
+         */
+        static IndexType nameToType(const string& accessMethod);
     };
 
 }  // namespace mongo