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compaction_level.go

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package litestream

import (

"fmt"

"time"

)

// SnapshotLevel represents the level which full snapshots are held.

const SnapshotLevel = 9

// DefaultCompactionLevels provides the canonical default compaction configuration.

// Level 0 is raw LTX files, higher levels compact at increasing intervals.

// These values are also used by cmd/litestream DefaultConfig().

var DefaultCompactionLevels = CompactionLevels{

{Level: 0, Interval: 0},

{Level: 1, Interval: 30 * time.Second},

{Level: 2, Interval: 5 * time.Minute},

{Level: 3, Interval: time.Hour},

}

// CompactionLevel represents a single part of a multi-level compaction.

// Each level merges LTX files from the previous level into larger time granularities.

type CompactionLevel struct {

// The numeric level. Must match the index in the list of levels.

Level int

// The frequency that the level is compacted from the previous level.

Interval time.Duration

}

// PrevCompactionAt returns the time when the last compaction occurred.

// Returns the current time if it is exactly a multiple of the level interval.

func (lvl *CompactionLevel) PrevCompactionAt(now time.Time) time.Time {

return now.Truncate(lvl.Interval).UTC()

}

// NextCompactionAt returns the time until the next compaction occurs.

// Returns the current time if it is exactly a multiple of the level interval.

func (lvl *CompactionLevel) NextCompactionAt(now time.Time) time.Time {

return lvl.PrevCompactionAt(now).Add(lvl.Interval)

}

// CompactionLevels represents a sorted slice of non-snapshot compaction levels.

type CompactionLevels []*CompactionLevel

// Level returns the compaction level at the given index.

// Returns an error if the index is a snapshot level or is out of bounds.

func (a CompactionLevels) Level(level int) (*CompactionLevel, error) {

if level == SnapshotLevel {

return nil, fmt.Errorf("invalid argument, snapshot level")

}

if level < 0 || level > a.MaxLevel() {

return nil, fmt.Errorf("level out of bounds: %d", level)

}

return a[level], nil

}

// MaxLevel return the highest non-snapshot compaction level.

func (a CompactionLevels) MaxLevel() int {

return len(a) - 1

}

// Validate returns an error if the levels are invalid.

func (a CompactionLevels) Validate() error {

if len(a) == 0 {

return fmt.Errorf("at least one compaction level is required")

}

for i, lvl := range a {

if i != lvl.Level {

return fmt.Errorf("compaction level number out of order: %d, expected %d", lvl.Level, i)

} else if lvl.Level > SnapshotLevel-1 {

return fmt.Errorf("compaction level cannot exceed %d", SnapshotLevel-1)

}

if lvl.Level == 0 && lvl.Interval != 0 {

return fmt.Errorf("cannot set interval on compaction level zero")

}

if lvl.Level != 0 && lvl.Interval <= 0 {

return fmt.Errorf("interval required for level %d", lvl.Level)

}

}

return nil

}

// IsValidLevel returns true if level is a valid compaction level number.

func (a CompactionLevels) IsValidLevel(level int) bool {

if level == SnapshotLevel {

return true

}

return level >= 0 && level < len(a)

}

// PrevLevel returns the previous compaction level.

// Returns -1 if there is no previous level.

func (a CompactionLevels) PrevLevel(level int) int {

if level == SnapshotLevel {

return a.MaxLevel()

}

return level - 1

}

// NextLevel returns the next compaction level.

// Returns -1 if there is no next level.

func (a CompactionLevels) NextLevel(level int) int {

if level == SnapshotLevel {

return -1

} else if level == a.MaxLevel() {

return SnapshotLevel

}

return level + 1

}