Module com.darkcollective.relix.ast
Package com.darkcollective.relix.ast

Record Class ReservoirSampleNode

java.lang.Object
java.lang.Record
com.darkcollective.relix.ast.ReservoirSampleNode
Record Components:
count - the exact number of rows to keep; non-negative
seed - the optional RNG seed for reproducible sampling; empty = non-deterministic
input - the relation to sample; must not be null
location - the source location of this node; never null
All Implemented Interfaces:
RelNode
public record ReservoirSampleNode(long count, Optional<Long> seed, RelNode input, SourceLocation location) extends Record implements RelNode
Reservoir (fixed-count) sampling (SAMPLE … ROWS) — keeps exactly count rows of input, chosen uniformly at random without replacement.

Where SampleNode (SAMPLE 0.1) is a per-row coin flip whose result size only averages p × |input|, this is the count-based form: SAMPLE 100 ROWS (R) returns exactly 100 rows (or all of them when the input has fewer than count). It is the composable, algebraic form of the ORDER BY RANDOM() LIMIT n idiom — but without the full sort.

Reproducibility: when seed is present the sampling is deterministic — identical runs produce identical row selections via Vitter's Algorithm R seeded with the given value. Without a seed, fresh randomness is drawn each run.

Examples:

  • SAMPLE 100 ROWS (Events) — keeps a uniform 100-row sample (non-deterministic)
  • SAMPLE 500 ROWS SEED 2026 (Events) — reproducible fixed-count sample

  • Constructor Details

    • ReservoirSampleNode

      public ReservoirSampleNode(long count, Optional<Long> seed, RelNode input, SourceLocation location)
      Creates an instance of a ReservoirSampleNode record class.
      Parameters:
      count - the value for the count record component
      seed - the value for the seed record component
      input - the value for the input record component
      location - the value for the location record component

    • ReservoirSampleNode

      public ReservoirSampleNode(long count, RelNode input, SourceLocation location)
      Convenience constructor without seed (non-deterministic); uses provided location.

    • ReservoirSampleNode

      public ReservoirSampleNode(long count, RelNode input)
      Convenience constructor for tests; uses SourceLocation.UNKNOWN and no seed.

  • Method Details

    • accept

      public <R> R accept(RelNodeVisitor<R> visitor)
      Specified by:
      accept in interface RelNode

    • toString

      public final String toString()
      Returns a string representation of this record class. The representation contains the name of the class, followed by the name and value of each of the record components.
      Specified by:
      toString in class Record
      Returns:
      a string representation of this object

    • hashCode

      public final int hashCode()
      Returns a hash code value for this object. The value is derived from the hash code of each of the record components.
      Specified by:
      hashCode in class Record
      Returns:
      a hash code value for this object

    • equals

      public final boolean equals(Object o)
      Indicates whether some other object is "equal to" this one. The objects are equal if the other object is of the same class and if all the record components are equal. Reference components are compared with Objects::equals(Object,Object); primitive components are compared with '=='.
      Specified by:
      equals in class Record
      Parameters:
      o - the object with which to compare
      Returns:
      true if this object is the same as the o argument; false otherwise.

    • count

      public long count()
      Returns the value of the count record component.
      Returns:
      the value of the count record component

    • seed

      public Optional<Long> seed()
      Returns the value of the seed record component.
      Returns:
      the value of the seed record component

    • input

      public RelNode input()
      Returns the value of the input record component.
      Returns:
      the value of the input record component

    • location

      public SourceLocation location()
      Returns the value of the location record component.
      Specified by:
      location in interface RelNode
      Returns:
      the value of the location record component