Add the GEQO Todo file too

doc/TODO.GEQO

+
+=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
+*         Things left to done for the PostgreSQL                    *
+=           Genetic Query Optimization (GEQO)                       =
+*              module implementation                                *
+=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
+* Martin Utesch		      * Institute of Automatic Control      *
+=                             = University of Mining and Technology =
+* utesch@aut.tu-freiberg.de   * Freiberg, Germany                   *
+=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=
+
+
+1.) Basic Improvements
+===============================================================
+
+a) improve freeing of memory when query is already processed:
+-------------------------------------------------------------
+with large JOIN queries the computing time spent for the genetic query
+optimization seems to be a mere *fraction* of the time Postgres
+needs for freeing memory via routine 'MemoryContextFree',
+file 'backend/utils/mmgr/mcxt.c';
+debugging showed that it get stucked in a loop of routine
+'OrderedElemPop', file 'backend/utils/mmgr/oset.c';
+the same problems arise with long queries when using the normal
+Postgres query optimization algorithm;
+
+b) improve genetic algorithm parameter settings:
+------------------------------------------------
+file 'backend/optimizer/geqo/geqo_params.c', routines
+'gimme_pool_size' and 'gimme_number_generations';
+we have to find a compromise for the parameter settings
+to satisfy two competing demands:
+1.  optimality of the query plan
+2.  computing time
+
+c) find better solution for integer overflow:
+---------------------------------------------
+file 'backend/optimizer/geqo/geqo_eval.c', routine
+'geqo_joinrel_size';
+the present hack for MAXINT overflow is to set the Postgres integer
+value of 'rel->size' to its logarithm;
+modifications of 'struct Rel' in 'backend/nodes/relation.h' will
+surely have severe impacts on the whole PostgreSQL implementation.
+
+d) find solution for exhausted memory:
+--------------------------------------
+that may occur with more than 10 relations involved in a query,
+file 'backend/optimizer/geqo/geqo_eval.c', routine
+'gimme_tree' which is recursively called;
+maybe I forgot something to be freed correctly, but I dunno what;
+of course the 'rel' data structure of the JOIN keeps growing and
+growing the more relations are packed into it;
+suggestions are welcome :-(
+
+
+2.) Further Improvements
+===============================================================
+Enable bushy query tree processing within PostgreSQL;
+that may improve the quality of query plans.