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