Method DropPrefix

db.go:1622–1663

DropPrefix would drop all the keys with the provided prefix. It does this in the following way: - Stop accepting new writes. - Stop memtable flushes before acquiring lock. Because we're acquring lock here and memtable flush stalls for lock, which leads to deadlock - Flush out all memtables, skipping

(prefixes ...[]byte)

// - Compact rest of the levels, Li->Li, picking tables which have Kp.
// - Resume memtable flushes, compactions and writes.
func (db *DB) DropPrefix(prefixes ...[]byte) error {
	db.opt.Infof("DropPrefix Called")
	f, err := db.prepareToDrop()
	if err != nil {
		return err
	}
	defer f()
	// Block all foreign interactions with memory tables.
	db.Lock()
	defer db.Unlock()

	db.imm = append(db.imm, db.mt)
	for _, memtable := range db.imm {
		if memtable.Empty() {
			memtable.DecrRef()
			continue
		}
		task := flushTask{
			mt: memtable,
			// Ensure that the head of value log gets persisted to disk.
			vptr:         db.vhead,
			dropPrefixes: prefixes,
		}
		db.opt.Debugf("Flushing memtable")
		if err := db.handleFlushTask(task); err != nil {
			db.opt.Errorf("While trying to flush memtable: %v", err)
			return err
		}
		memtable.DecrRef()
	}
	db.stopCompactions()
	defer db.startCompactions()
	db.imm = db.imm[:0]
	db.mt = skl.NewSkiplist(arenaSize(db.opt))

	// Drop prefixes from the levels.
	if err := db.lc.dropPrefixes(prefixes); err != nil {
		return err
	}
	db.opt.Infof("DropPrefix done")
	return nil
}

// KVList contains a list of key-value pairs.
type KVList = pb.KVList