planner

func Optimize ¶

func Optimize(s *stream.Stream, tx *database.Transaction, params []expr.Param) (*stream.Stream, error)

Optimize takes a tree, applies a list of optimization rules and returns an optimized tree. Depending on the rule, the tree may be modified in place or replaced by a new one.

func PrecalculateExprRule ¶

func PrecalculateExprRule(s *stream.Stream, _ *database.Transaction, params []expr.Param) (*stream.Stream, error)

PrecalculateExprRule evaluates any constant sub-expression that can be evaluated before running the query and replaces it by the result of the evaluation. The result of constant sub-expressions, like "3 + 4", is always the same and thus can be precalculated. Examples:

3 + 4 --> 7
3 + 1 > 10 - a --> 4 > 10 - a

func RemoveUnnecessaryDistinctNodeRule ¶

func RemoveUnnecessaryDistinctNodeRule(s *stream.Stream, tx *database.Transaction, _ []expr.Param) (*stream.Stream, error)

RemoveUnnecessaryDistinctNodeRule removes any Dedup nodes where projection is already unique.

func RemoveUnnecessaryFilterNodesRule ¶

func RemoveUnnecessaryFilterNodesRule(s *stream.Stream, _ *database.Transaction, _ []expr.Param) (*stream.Stream, error)

RemoveUnnecessaryFilterNodesRule removes any filter node whose condition is a constant expression that evaluates to a truthy value. if it evaluates to a falsy value, it considers that the tree will not stream any document, so it returns an empty tree.

func RemoveUnnecessaryProjection ¶

func RemoveUnnecessaryProjection(s *stream.Stream, _ *database.Transaction, _ []expr.Param) (*stream.Stream, error)

RemoveUnnecessaryProjection removes any project node whose expression is a wildcard only.

func SplitANDConditionRule ¶

func SplitANDConditionRule(s *stream.Stream, _ *database.Transaction, _ []expr.Param) (*stream.Stream, error)

SplitANDConditionRule splits any filter node whose condition is one or more AND operators into one or more filter nodes. The condition won't be split if the expression tree contains an OR operation. Example:

this:
  filter(a > 2 AND b != 3 AND c < 2)
becomes this:
  filter(a > 2)
  filter(b != 3)
  filter(c < 2)

func UseIndexBasedOnFilterNodeRule ¶

func UseIndexBasedOnFilterNodeRule(s *stream.Stream, tx *database.Transaction, params []expr.Param) (*stream.Stream, error)

UseIndexBasedOnFilterNodeRule scans the tree for filter nodes whose conditions are operators that satisfies the following criterias: - is a comparison operator - one of its operands is a path expression that is indexed - the other operand is a literal value or a parameter

If one or many are found, it will replace the input node by an indexInputNode using this index, removing the now irrelevant filter nodes.

TODO(asdine): add support for ORDER BY TODO(jh): clarify cost code in composite indexes case