github.com/m3db/m3@v1.5.0/src/dbnode/storage/dice.go (about)

     1  // Copyright (c) 2019 Uber Technologies, Inc.
     2  //
     3  // Permission is hereby granted, free of charge, to any person obtaining a copy
     4  // of this software and associated documentation files (the "Software"), to deal
     5  // in the Software without restriction, including without limitation the rights
     6  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
     7  // copies of the Software, and to permit persons to whom the Software is
     8  // furnished to do so, subject to the following conditions:
     9  //
    10  // The above copyright notice and this permission notice shall be included in
    11  // all copies or substantial portions of the Software.
    12  //
    13  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    14  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    15  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    16  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    17  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    18  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    19  // THE SOFTWARE.
    20  
    21  package storage
    22  
    23  import (
    24  	"fmt"
    25  
    26  	"github.com/MichaelTJones/pcg"
    27  )
    28  
    29  // dice is an interface that allows for random sampling.
    30  type dice interface {
    31  	// Rate returns the sampling rate of this dice: a number in (0.0, 1.0].
    32  	Rate() float64
    33  
    34  	// Roll returns whether the dice roll succeeded.
    35  	Roll() bool
    36  }
    37  
    38  // newDice constructs a new dice based on a given success rate.
    39  func newDice(rate float64) (dice, error) {
    40  	if rate <= 0.0 || rate > 1.0 {
    41  		return nil, fmt.Errorf("invalid sample rate %f", rate)
    42  	}
    43  
    44  	return &epoch{
    45  		r:   uint64(1.0 / rate),
    46  		rng: pcg.NewPCG64(),
    47  	}, nil
    48  }
    49  
    50  type epoch struct {
    51  	r   uint64
    52  	rng *pcg.PCG64
    53  }
    54  
    55  func (d *epoch) Rate() float64 {
    56  	return 1 / float64(d.r)
    57  }
    58  
    59  func (d *epoch) Roll() bool {
    60  	return d.rng.Random()%d.r == 0
    61  }