swarm: add database abstractions (shed package) (#18183)
This commit is contained in:
Janoš Guljaš
committed by
Anton Evangelatov
Anton Evangelatov
parent
4f0d978eaa
commit
c207edf2a3
332
swarm/shed/example_store_test.go
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332
swarm/shed/example_store_test.go
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// Copyright 2018 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package shed_test
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import (
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"bytes"
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"context"
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"encoding/binary"
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"fmt"
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"io/ioutil"
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"log"
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"os"
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"time"
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"github.com/ethereum/go-ethereum/swarm/shed"
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"github.com/ethereum/go-ethereum/swarm/storage"
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"github.com/syndtr/goleveldb/leveldb"
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)
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// Store holds fields and indexes (including their encoding functions)
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// and defines operations on them by composing data from them.
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// It implements storage.ChunkStore interface.
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// It is just an example without any support for parallel operations
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// or real world implementation.
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type Store struct {
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db *shed.DB
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// fields and indexes
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schemaName shed.StringField
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sizeCounter shed.Uint64Field
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accessCounter shed.Uint64Field
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retrievalIndex shed.Index
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accessIndex shed.Index
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gcIndex shed.Index
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}
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// New returns new Store. All fields and indexes are initialized
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// and possible conflicts with schema from existing database is checked
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// automatically.
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func New(path string) (s *Store, err error) {
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db, err := shed.NewDB(path)
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if err != nil {
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return nil, err
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}
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s = &Store{
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db: db,
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}
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// Identify current storage schema by arbitrary name.
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s.schemaName, err = db.NewStringField("schema-name")
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if err != nil {
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return nil, err
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}
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// Global ever incrementing index of chunk accesses.
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s.accessCounter, err = db.NewUint64Field("access-counter")
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if err != nil {
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return nil, err
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}
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// Index storing actual chunk address, data and store timestamp.
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s.retrievalIndex, err = db.NewIndex("Address->StoreTimestamp|Data", shed.IndexFuncs{
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EncodeKey: func(fields shed.IndexItem) (key []byte, err error) {
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return fields.Address, nil
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},
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DecodeKey: func(key []byte) (e shed.IndexItem, err error) {
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e.Address = key
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return e, nil
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},
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EncodeValue: func(fields shed.IndexItem) (value []byte, err error) {
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b := make([]byte, 8)
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binary.BigEndian.PutUint64(b, uint64(fields.StoreTimestamp))
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value = append(b, fields.Data...)
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return value, nil
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},
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DecodeValue: func(value []byte) (e shed.IndexItem, err error) {
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e.StoreTimestamp = int64(binary.BigEndian.Uint64(value[:8]))
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e.Data = value[8:]
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return e, nil
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},
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})
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if err != nil {
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return nil, err
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}
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// Index storing access timestamp for a particular address.
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// It is needed in order to update gc index keys for iteration order.
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s.accessIndex, err = db.NewIndex("Address->AccessTimestamp", shed.IndexFuncs{
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EncodeKey: func(fields shed.IndexItem) (key []byte, err error) {
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return fields.Address, nil
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},
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DecodeKey: func(key []byte) (e shed.IndexItem, err error) {
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e.Address = key
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return e, nil
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},
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EncodeValue: func(fields shed.IndexItem) (value []byte, err error) {
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b := make([]byte, 8)
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binary.BigEndian.PutUint64(b, uint64(fields.AccessTimestamp))
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return b, nil
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},
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DecodeValue: func(value []byte) (e shed.IndexItem, err error) {
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e.AccessTimestamp = int64(binary.BigEndian.Uint64(value))
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return e, nil
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},
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})
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if err != nil {
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return nil, err
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}
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// Index with keys ordered by access timestamp for garbage collection prioritization.
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s.gcIndex, err = db.NewIndex("AccessTimestamp|StoredTimestamp|Address->nil", shed.IndexFuncs{
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EncodeKey: func(fields shed.IndexItem) (key []byte, err error) {
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b := make([]byte, 16, 16+len(fields.Address))
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binary.BigEndian.PutUint64(b[:8], uint64(fields.AccessTimestamp))
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binary.BigEndian.PutUint64(b[8:16], uint64(fields.StoreTimestamp))
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key = append(b, fields.Address...)
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return key, nil
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},
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DecodeKey: func(key []byte) (e shed.IndexItem, err error) {
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e.AccessTimestamp = int64(binary.BigEndian.Uint64(key[:8]))
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e.StoreTimestamp = int64(binary.BigEndian.Uint64(key[8:16]))
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e.Address = key[16:]
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return e, nil
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},
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EncodeValue: func(fields shed.IndexItem) (value []byte, err error) {
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return nil, nil
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},
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DecodeValue: func(value []byte) (e shed.IndexItem, err error) {
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return e, nil
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},
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})
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if err != nil {
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return nil, err
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}
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return s, nil
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}
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// Put stores the chunk and sets it store timestamp.
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func (s *Store) Put(_ context.Context, ch storage.Chunk) (err error) {
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return s.retrievalIndex.Put(shed.IndexItem{
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Address: ch.Address(),
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Data: ch.Data(),
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StoreTimestamp: time.Now().UTC().UnixNano(),
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})
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}
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// Get retrieves a chunk with the provided address.
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// It updates access and gc indexes by removing the previous
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// items from them and adding new items as keys of index entries
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// are changed.
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func (s *Store) Get(_ context.Context, addr storage.Address) (c storage.Chunk, err error) {
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batch := new(leveldb.Batch)
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// Get the chunk data and storage timestamp.
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item, err := s.retrievalIndex.Get(shed.IndexItem{
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Address: addr,
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})
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if err != nil {
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if err == leveldb.ErrNotFound {
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return nil, storage.ErrChunkNotFound
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}
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return nil, err
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}
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// Get the chunk access timestamp.
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accessItem, err := s.accessIndex.Get(shed.IndexItem{
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Address: addr,
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})
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switch err {
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case nil:
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// Remove gc index entry if access timestamp is found.
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err = s.gcIndex.DeleteInBatch(batch, shed.IndexItem{
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Address: item.Address,
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StoreTimestamp: accessItem.AccessTimestamp,
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AccessTimestamp: item.StoreTimestamp,
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})
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if err != nil {
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return nil, err
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}
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case leveldb.ErrNotFound:
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// Access timestamp is not found. Do not do anything.
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// This is the firs get request.
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default:
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return nil, err
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}
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// Specify new access timestamp
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accessTimestamp := time.Now().UTC().UnixNano()
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// Put new access timestamp in access index.
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err = s.accessIndex.PutInBatch(batch, shed.IndexItem{
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Address: addr,
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AccessTimestamp: accessTimestamp,
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})
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if err != nil {
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return nil, err
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}
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// Put new access timestamp in gc index.
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err = s.gcIndex.PutInBatch(batch, shed.IndexItem{
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Address: item.Address,
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AccessTimestamp: accessTimestamp,
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StoreTimestamp: item.StoreTimestamp,
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})
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if err != nil {
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return nil, err
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}
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// Increment access counter.
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// Currently this information is not used anywhere.
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_, err = s.accessCounter.IncInBatch(batch)
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if err != nil {
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return nil, err
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}
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// Write the batch.
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err = s.db.WriteBatch(batch)
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if err != nil {
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return nil, err
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}
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// Return the chunk.
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return storage.NewChunk(item.Address, item.Data), nil
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}
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// CollectGarbage is an example of index iteration.
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// It provides no reliable garbage collection functionality.
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func (s *Store) CollectGarbage() (err error) {
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const maxTrashSize = 100
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maxRounds := 10 // arbitrary number, needs to be calculated
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// Run a few gc rounds.
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for roundCount := 0; roundCount < maxRounds; roundCount++ {
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var garbageCount int
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// New batch for a new cg round.
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trash := new(leveldb.Batch)
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// Iterate through all index items and break when needed.
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err = s.gcIndex.IterateAll(func(item shed.IndexItem) (stop bool, err error) {
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// Remove the chunk.
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err = s.retrievalIndex.DeleteInBatch(trash, item)
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if err != nil {
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return false, err
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}
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// Remove the element in gc index.
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err = s.gcIndex.DeleteInBatch(trash, item)
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if err != nil {
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return false, err
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}
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// Remove the relation in access index.
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err = s.accessIndex.DeleteInBatch(trash, item)
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if err != nil {
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return false, err
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}
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garbageCount++
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if garbageCount >= maxTrashSize {
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return true, nil
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}
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return false, nil
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})
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if err != nil {
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return err
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}
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if garbageCount == 0 {
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return nil
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}
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err = s.db.WriteBatch(trash)
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if err != nil {
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return err
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}
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}
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return nil
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}
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// GetSchema is an example of retrieveing the most simple
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// string from a database field.
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func (s *Store) GetSchema() (name string, err error) {
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name, err = s.schemaName.Get()
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if err == leveldb.ErrNotFound {
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return "", nil
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}
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return name, err
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}
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// GetSchema is an example of storing the most simple
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// string in a database field.
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func (s *Store) PutSchema(name string) (err error) {
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return s.schemaName.Put(name)
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}
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// Close closes the underlying database.
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func (s *Store) Close() error {
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return s.db.Close()
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}
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// Example_store constructs a simple storage implementation using shed package.
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func Example_store() {
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dir, err := ioutil.TempDir("", "ephemeral")
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if err != nil {
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log.Fatal(err)
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}
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defer os.RemoveAll(dir)
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s, err := New(dir)
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if err != nil {
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log.Fatal(err)
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}
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defer s.Close()
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ch := storage.GenerateRandomChunk(1024)
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err = s.Put(context.Background(), ch)
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if err != nil {
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log.Fatal(err)
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}
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got, err := s.Get(context.Background(), ch.Address())
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if err != nil {
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log.Fatal(err)
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}
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fmt.Println(bytes.Equal(got.Data(), ch.Data()))
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//Output: true
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}
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