Method RunValueLogGC

db.go:1198–1229

RunValueLogGC triggers a value log garbage collection. It picks value log files to perform GC based on statistics that are collected during compactions. If no such statistics are available, then log files are picked in random order. The process stops as soon as the first log file is encountered wh

(discardRatio float64)

// Note: Every time GC is run, it would produce a spike of activity on the LSM
// tree.
func (db *DB) RunValueLogGC(discardRatio float64) error {
	if db.opt.InMemory {
		return ErrGCInMemoryMode
	}
	if discardRatio >= 1.0 || discardRatio <= 0.0 {
		return ErrInvalidRequest
	}

	// startLevel is the level from which we should search for the head key. When badger is running
	// with KeepL0InMemory flag, all tables on L0 are kept in memory. This means we should pick head
	// key from Level 1 onwards because if we pick the headkey from Level 0 we might end up losing
	// data. See test TestL0GCBug.
	startLevel := 0
	if db.opt.KeepL0InMemory {
		startLevel = 1
	}
	// Find head on disk
	headKey := y.KeyWithTs(head, math.MaxUint64)
	// Need to pass with timestamp, lsm get removes the last 8 bytes and compares key
	val, err := db.lc.get(headKey, nil, startLevel)
	if err != nil {
		return errors.Wrap(err, "Retrieving head from on-disk LSM")
	}

	var head valuePointer
	if len(val.Value) > 0 {
		head.Decode(val.Value)
	}

	// Pick a log file and run GC
	return db.vlog.runGC(discardRatio, head)
}

// Size returns the size of lsm and value log files in bytes. It can be used to decide how often to
// call RunValueLogGC.