Minor - add sql index

documentation/optimization.html

@@ -232,6 +232,8 @@ ALTER TABLE c_lp_item_view ADD INDEX idx_clpiv_c_i_v (c_id, id, view_count);
         ALTER TABLE c_document add index idx_cdoc_sid (session_id);
         ALTER TABLE c_item_property ADD INDEX idx_item_property_visibility (visibility);
         ALTER TABLE track_e_attempt ADD INDEX idx_track_e_attempt_tms (tms);
+        ALTER TABLE track_e_login ADD INDEX idx_track_e_login_date (login_date);
+
     </pre>
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 <h2><a name="3.Indexes-caching"></a>3. Indexes caching</h2>