github.com/bhojpur/cache@v0.0.4/pkg/memory/compact.go

package memory

// Copyright (c) 2018 Bhojpur Consulting Private Limited, India. All rights reserved.

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

// Compact will create a copy of the source DB and in the destination DB. This may
// reclaim space that the source database no longer has use for. txMaxSize can be
// used to limit the transactions size of this process and may trigger intermittent
// commits. A value of zero will ignore transaction sizes.
func Compact(dst, src *DB, txMaxSize int64) error {
	// commit regularly, or we'll run out of memory for large datasets if using
	// one transaction.
	var size int64
	tx, err := dst.Begin(true)
	if err != nil {
		return err
	}
	defer tx.Rollback()

	if err := walk(src, func(keys [][]byte, k, v []byte, seq uint64) error {
		// On each key/value, check if we have exceeded tx size.
		sz := int64(len(k) + len(v))
		if size+sz > txMaxSize && txMaxSize != 0 {
			// Commit previous transaction.
			if err := tx.Commit(); err != nil {
				return err
			}

			// Start new transaction.
			tx, err = dst.Begin(true)
			if err != nil {
				return err
			}
			size = 0
		}
		size += sz

		// Create bucket on the root transaction if this is the first level.
		nk := len(keys)
		if nk == 0 {
			bkt, err := tx.CreateBucket(k)
			if err != nil {
				return err
			}
			if err := bkt.SetSequence(seq); err != nil {
				return err
			}
			return nil
		}

		// Create buckets on subsequent levels, if necessary.
		b := tx.Bucket(keys[0])
		if nk > 1 {
			for _, k := range keys[1:] {
				b = b.Bucket(k)
			}
		}

		// Fill the entire page for best compaction.
		b.FillPercent = 1.0

		// If there is no value then this is a bucket call.
		if v == nil {
			bkt, err := b.CreateBucket(k)
			if err != nil {
				return err
			}
			if err := bkt.SetSequence(seq); err != nil {
				return err
			}
			return nil
		}

		// Otherwise treat it as a key/value pair.
		return b.Put(k, v)
	}); err != nil {
		return err
	}

	return tx.Commit()
}

// walkFunc is the type of the function called for keys (buckets and "normal"
// values) discovered by Walk. keys is the list of keys to descend to the bucket
// owning the discovered key/value pair k/v.
type walkFunc func(keys [][]byte, k, v []byte, seq uint64) error

// walk walks recursively the Bhojpur Cache in-memory database db, calling walkFn
// for each key it finds.
func walk(db *DB, walkFn walkFunc) error {
	return db.View(func(tx *Tx) error {
		return tx.ForEach(func(name []byte, b *Bucket) error {
			return walkBucket(b, nil, name, nil, b.Sequence(), walkFn)
		})
	})
}

func walkBucket(b *Bucket, keypath [][]byte, k, v []byte, seq uint64, fn walkFunc) error {
	// Execute callback.
	if err := fn(keypath, k, v, seq); err != nil {
		return err
	}

	// If this is not a Bucket then stop.
	if v != nil {
		return nil
	}

	// Iterate over each child key/value.
	keypath = append(keypath, k)
	return b.ForEach(func(k, v []byte) error {
		if v == nil {
			bkt := b.Bucket(k)
			return walkBucket(bkt, keypath, k, nil, bkt.Sequence(), fn)
		}
		return walkBucket(b, keypath, k, v, b.Sequence(), fn)
	})
}