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* Things left to done for the PostgreSQL *
= Genetic Query Optimization (GEQO) =
* module implementation *
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* Martin Utesch * Institute of Automatic Control *
= = University of Mining and Technology =
* utesch@aut.tu-freiberg.de * Freiberg, Germany *
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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.
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