Internal: Add documentation about possible optimization queries

documentation/optimization.html

@@ -233,6 +233,9 @@ ALTER TABLE c_lp_item_view ADD INDEX idx_clpiv_c_i_v (c_id, id, view_count);
         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);
+        ALTER TABLE track_e_course_access ADD INDEX idx_teca_countconn (c_id, session_id, login_course_date);
+        ALTER TABLE extra_field_values ADD INDEX idx_efv_fv1 (field_id, value(1));
+        ALTER TABLE message ADD INDEX idx_message_senddate (send_date);
 
     </pre>
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