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Commitb1577a7

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New cost model for planning, incorporating a penalty for random page
accesses versus sequential accesses, a (very crude) estimate of theeffects of caching on random page accesses, and cost to evaluate WHERE-clause expressions. Export critical parameters for this model as SETvariables. Also, create SET variables for the planner's enable flags(enable_seqscan, enable_indexscan, etc) so that these can be controlledmore conveniently than via PGOPTIONS.Planner now estimates both startup cost (cost before retrievingfirst tuple) and total cost of each path, so it can optimize querieswith LIMIT on a reasonable basis by interpolating between these costs.Same facility is a win for EXISTS(...) subqueries and some other cases.Redesign pathkey representation to achieve a major speedup in planning(I saw as much as 5X on a 10-way join); also minor changes in plannerto reduce memory consumption by recycling discarded Path nodes andnot constructing unnecessary lists.Minor cleanups to display more-plausible costs in some cases inEXPLAIN output.Initdb forced by change in interface to index cost estimationfunctions.
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‎doc/src/sgml/libpq++.sgml

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sets the default mode for the genetic optimizer.
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sets the default mode to allow or disable right-sided plans in the optimizer.
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sets the default cost for heap searches for the optimizer.
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<envar>PGCOSTINDEX</envar>
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sets the default cost for indexed searches for the optimizer.
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‎doc/src/sgml/libpq.sgml

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