Class Optimizer

java.lang.Object

org.h2.command.query.Optimizer

class Optimizer
extends Object

The optimizer is responsible to find the best execution plan for a given query.

Field Summary

Fields

Modifier and Type	Field	Description
private final AllColumnsForPlan	allColumnsSet
private Plan	bestPlan
private final Expression	condition
private double	cost
private final TableFilter[]	filters
private static final int	MAX_BRUTE_FORCE
private static final int	MAX_BRUTE_FORCE_FILTERS
private static final int	MAX_GENETIC
private Random	random
private final SessionLocal	session
private long	startNs
private BitSet	switched
private TableFilter	topFilter

Constructor Summary

Constructors

Constructor	Description
Optimizer(TableFilter[] filters, Expression condition, SessionLocal session)

Method Summary

Modifier and Type	Method	Description
private void	calculateBestPlan()
private void	calculateBruteForceAll()
private void	calculateBruteForceSome()
private void	calculateFakePlan()
private void	calculateGenetic()
private boolean	canStop(int x)
(package private) double	getCost()
private static int	getMaxBruteForceFilters(int filterCount)	How many filter to calculate using brute force.
TableFilter	getTopFilter()
(package private) void	optimize(boolean parse)	Calculate the best query plan to use.
private void	shuffleAll(TableFilter[] f)
private boolean	shuffleTwo(TableFilter[] f)
private boolean	testPlan(TableFilter[] list)

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

MAX_BRUTE_FORCE_FILTERS

private static final int MAX_BRUTE_FORCE_FILTERS

See Also:

• Constant Field Values

MAX_BRUTE_FORCE

private static final int MAX_BRUTE_FORCE

See Also:

• Constant Field Values

MAX_GENETIC

private static final int MAX_GENETIC

See Also:

• Constant Field Values

startNs

private long startNs

switched

private BitSet switched

filters

private final TableFilter[] filters

condition

private final Expression condition

session

private final SessionLocal session

bestPlan

private Plan bestPlan

topFilter

private TableFilter topFilter

cost

private double cost

random

private Random random

allColumnsSet

private final AllColumnsForPlan allColumnsSet

Constructor Details

Optimizer

Optimizer(TableFilter[] filters,
 Expression condition,
 SessionLocal session)

Method Details

getMaxBruteForceFilters

private static int getMaxBruteForceFilters(int filterCount)

How many filter to calculate using brute force. The remaining filters are selected using a greedy algorithm which has a runtime of (1 + 2 + ... + n) = (n * (n-1) / 2) for n filters. The brute force algorithm has a runtime of n * (n-1) * ... * (n-m) when calculating m brute force of n total. The combined runtime is (brute force) * (greedy).

Parameters:

filterCount - the number of filters total

Returns:

the number of filters to calculate using brute force

calculateBestPlan

private void calculateBestPlan()

calculateFakePlan

private void calculateFakePlan()

canStop

private boolean canStop(int x)

calculateBruteForceAll

private void calculateBruteForceAll()

calculateBruteForceSome

private void calculateBruteForceSome()

calculateGenetic

private void calculateGenetic()

testPlan

private boolean testPlan(TableFilter[] list)

shuffleAll

private void shuffleAll(TableFilter[] f)

shuffleTwo

private boolean shuffleTwo(TableFilter[] f)

optimize

void optimize(boolean parse)

Calculate the best query plan to use.

Parameters:

parse - If we do not need to really get the best plan because it is a view parsing stage.

getTopFilter

public TableFilter getTopFilter()

getCost

double getCost()