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452 lines
10 KiB
Go
452 lines
10 KiB
Go
// Package store provides a distributed SQLite instance.
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//
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// Distributed consensus is provided via the Raft algorithm.
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package store
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import (
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"bytes"
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"encoding/json"
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"errors"
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"fmt"
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"io"
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"io/ioutil"
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"log"
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"net"
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"os"
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"path/filepath"
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"sync"
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"time"
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"github.com/hashicorp/raft"
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"github.com/hashicorp/raft-boltdb"
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sql "github.com/otoolep/rqlite/db"
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)
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const (
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retainSnapshotCount = 2
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raftTimeout = 10 * time.Second
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sqliteFile = "db.sqlite"
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leaderWaitDelay = 100 * time.Millisecond
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appliedWaitDelay = 100 * time.Millisecond
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)
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var (
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// ErrFieldsRequired is returned when a node attempts to execute a leader-only
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// operation.
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ErrNotLeader = errors.New("not leader")
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)
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type commandType int
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const (
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execute = iota
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query
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)
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type command struct {
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typ commandType `json:"typ,omitempty"`
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Tx bool `json:"tx,omitempty"`
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Queries []string `json:"queries,omitempty"`
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Timings bool `json:"timings",omitempty"`
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}
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// Store is a SQLite database, where all changes are made via Raft consensus.
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type Store struct {
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raftDir string
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raftBind string
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mu sync.RWMutex // Sync access between queries and snapshots.
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ln *networkLayer // Raft network between nodes.
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raft *raft.Raft // The consensus mechanism.
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dbConf *sql.Config // SQLite database config.
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dbPath string // Path to database file.
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db *sql.DB // The underlying SQLite store.
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logger *log.Logger
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}
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// New returns a new Store.
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func New(dbConf *sql.Config, dir, bind string) *Store {
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dbPath := filepath.Join(dir, sqliteFile)
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if dbConf.Memory {
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dbPath = ":memory:"
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}
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return &Store{
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raftDir: dir,
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raftBind: bind,
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dbConf: dbConf,
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dbPath: dbPath,
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logger: log.New(os.Stderr, "[store] ", log.LstdFlags),
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}
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}
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// Open opens the store. If enableSingle is set, and there are no existing peers,
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// then this node becomes the first node, and therefore leader, of the cluster.
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func (s *Store) Open(enableSingle bool) error {
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if err := os.MkdirAll(s.raftDir, 0755); err != nil {
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return err
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}
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// Create the database. Unless it's a memory-based database, tt must be deleted
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if !s.dbConf.Memory {
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// as it will be rebuilt from (possibly) a snapshot and committed log entries.
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if err := os.Remove(s.dbPath); err != nil && !os.IsNotExist(err) {
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return err
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}
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}
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db, err := sql.OpenWithConfiguration(s.dbPath, s.dbConf)
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if err != nil {
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return err
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}
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s.db = db
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s.logger.Println("SQLite database opened at", s.dbConf.FQDSN(s.dbPath))
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// Setup Raft configuration.
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config := raft.DefaultConfig()
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// Check for any existing peers.
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peers, err := readPeersJSON(filepath.Join(s.raftDir, "peers.json"))
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if err != nil {
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return err
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}
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// Allow the node to entry single-mode, potentially electing itself, if
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// explicitly enabled and there is only 1 node in the cluster already.
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if enableSingle && len(peers) <= 1 {
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s.logger.Println("enabling single-node mode")
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config.EnableSingleNode = true
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config.DisableBootstrapAfterElect = false
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}
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// Setup Raft communication.
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ln, err := net.Listen("tcp", s.raftBind)
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if err != nil {
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return err
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}
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s.ln = newnetworkLayer(ln)
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transport := raft.NewNetworkTransport(s.ln, 3, 10*time.Second, os.Stderr)
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// Create peer storage.
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peerStore := raft.NewJSONPeers(s.raftDir, transport)
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// Create the snapshot store. This allows Raft to truncate the log.
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snapshots, err := raft.NewFileSnapshotStore(s.raftDir, retainSnapshotCount, os.Stderr)
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if err != nil {
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return fmt.Errorf("file snapshot store: %s", err)
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}
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// Create the log store and stable store.
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logStore, err := raftboltdb.NewBoltStore(filepath.Join(s.raftDir, "raft.db"))
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if err != nil {
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return fmt.Errorf("new bolt store: %s", err)
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}
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// Instantiate the Raft system.
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ra, err := raft.NewRaft(config, s, logStore, logStore, snapshots, peerStore, transport)
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if err != nil {
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return fmt.Errorf("new raft: %s", err)
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}
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s.raft = ra
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return nil
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}
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// Close closes the store.
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func (s *Store) Close() error {
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if err := s.db.Close(); err != nil {
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return err
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}
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f := s.raft.Shutdown()
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if e := f.(raft.Future); e.Error() != nil {
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return e.Error()
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}
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return nil
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}
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// Path returns the path to the store's storage directory.
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func (s *Store) Path() string {
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return s.raftDir
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}
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func (s *Store) Addr() net.Addr {
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return s.ln.Addr()
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}
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// Leader returns the current leader. Returns a blank string if there is
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// no leader.
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func (s *Store) Leader() string {
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return s.raft.Leader()
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}
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// WaitForLeader blocks until a leader is detected, or the timeout expires.
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func (s *Store) WaitForLeader(timeout time.Duration) (string, error) {
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tck := time.NewTicker(leaderWaitDelay)
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defer tck.Stop()
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tmr := time.NewTimer(timeout)
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defer tmr.Stop()
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for {
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select {
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case <-tck.C:
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l := s.Leader()
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if l != "" {
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return l, nil
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}
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case <-tmr.C:
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return "", fmt.Errorf("timeout expired")
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}
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}
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}
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// WaitForAppliedIndex blocks until a given log index has been applied,
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// or the timeout expires.
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func (s *Store) WaitForAppliedIndex(idx uint64, timeout time.Duration) error {
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tck := time.NewTicker(appliedWaitDelay)
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defer tck.Stop()
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tmr := time.NewTimer(timeout)
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defer tmr.Stop()
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for {
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select {
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case <-tck.C:
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if s.raft.AppliedIndex() >= idx {
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return nil
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}
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case <-tmr.C:
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return fmt.Errorf("timeout expired")
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}
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}
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}
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// Stats returns stats for the store.
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func (s *Store) Stats() (map[string]interface{}, error) {
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dbStatus := map[string]interface{}{
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"path": s.dbPath,
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"dns": s.dbConf.FQDSN(s.dbPath),
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"version": sql.DBVersion,
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}
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status := map[string]interface{}{
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"raft": s.raft.Stats(),
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"addr": s.Addr().String(),
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"leader": s.Leader(),
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"sqlite3": dbStatus,
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}
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return status, nil
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}
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// Execute executes queries that return no rows, but do modify the database.
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func (s *Store) Execute(queries []string, tx bool) ([]*sql.Result, error) {
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if s.raft.State() != raft.Leader {
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return nil, ErrNotLeader
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}
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c := &command{
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typ: execute,
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Tx: tx,
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Queries: queries,
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}
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b, err := json.Marshal(c)
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if err != nil {
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return nil, err
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}
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f := s.raft.Apply(b, raftTimeout)
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if e := f.(raft.Future); e.Error() != nil {
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return nil, e.Error()
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}
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r := f.Response().(*fsmExecuteResponse)
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return r.results, r.error
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}
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// Backup return a consistent snapshot of the underlying database.
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func (s *Store) Backup(leader bool) ([]byte, error) {
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if leader && s.raft.State() != raft.Leader {
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return nil, fmt.Errorf("not leader")
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}
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f, err := ioutil.TempFile("", "rqlilte-bak-")
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if err != nil {
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return nil, err
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}
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f.Close()
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defer os.Remove(f.Name())
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if err := s.db.Backup(f.Name()); err != nil {
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return nil, err
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}
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b, err := ioutil.ReadFile(f.Name())
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if err != nil {
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return nil, err
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}
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return b, nil
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}
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// Query executes queries that return rows, and do not modify the database.
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func (s *Store) Query(queries []string, tx, leader, verify bool) ([]*sql.Rows, error) {
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// Allow concurrent queries.
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s.mu.RLock()
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defer s.mu.RUnlock()
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if leader && s.raft.State() != raft.Leader {
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return nil, ErrNotLeader
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}
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if verify {
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f := s.raft.VerifyLeader()
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if e := f.(raft.Future); e.Error() != nil {
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return nil, e.Error()
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}
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}
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r, err := s.db.Query(queries, tx, true)
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return r, err
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}
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// Join joins a node, located at addr, to this store. The node must be ready to
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// respond to Raft communications at that address.
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func (s *Store) Join(addr string) error {
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s.logger.Printf("received request to join node at %s", addr)
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f := s.raft.AddPeer(addr)
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if f.Error() != nil {
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return f.Error()
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}
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s.logger.Printf("node at %s joined successfully", addr)
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return nil
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}
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type fsmExecuteResponse struct {
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results []*sql.Result
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error error
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}
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type fsmQueryResponse struct {
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rows []*sql.Rows
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error error
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}
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// Apply applies a Raft log entry to the database.
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func (s *Store) Apply(l *raft.Log) interface{} {
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var c command
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if err := json.Unmarshal(l.Data, &c); err != nil {
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panic(fmt.Sprintf("failed to unmarshal command: %s", err.Error()))
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}
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if c.typ == execute {
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r, err := s.db.Execute(c.Queries, c.Tx, c.Timings)
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return &fsmExecuteResponse{results: r, error: err}
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}
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r, err := s.db.Query(c.Queries, c.Tx, c.Timings)
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return &fsmQueryResponse{rows: r, error: err}
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}
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// Snapshot returns a snapshot of the database. The caller must ensure that
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// no transaction is taking place during this call. Hashsicorp Raft guarantees
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// that this function will not be called concurrently with Apply.
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//
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// http://sqlite.org/howtocorrupt.html states it is safe to do this
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// as long as no transaction is in progress.
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func (s *Store) Snapshot() (raft.FSMSnapshot, error) {
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// Ensure only one snapshot can take place at once, and block all queries.
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s.mu.Lock()
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defer s.mu.Unlock()
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f, err := ioutil.TempFile("", "rqlilte-snap-")
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if err != nil {
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return nil, err
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}
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f.Close()
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defer os.Remove(f.Name())
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if err := s.db.Backup(f.Name()); err != nil {
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return nil, err
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}
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b, err := ioutil.ReadFile(f.Name())
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if err != nil {
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log.Printf("Failed to generate snapshot: %s", err.Error())
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return nil, err
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}
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return &fsmSnapshot{data: b}, nil
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}
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// Restore restores the database to a previous state.
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func (s *Store) Restore(rc io.ReadCloser) error {
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if err := os.Remove(s.dbPath); err != nil && !os.IsNotExist(err) {
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return err
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}
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b, err := ioutil.ReadAll(rc)
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if err != nil {
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return err
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}
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if err := ioutil.WriteFile(s.dbPath, b, 0660); err != nil {
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return err
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}
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db, err := sql.OpenWithConfiguration(s.dbPath, s.dbConf)
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if err != nil {
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return err
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}
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s.db = db
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return nil
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}
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type fsmSnapshot struct {
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data []byte
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}
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// Persist writes the snapshot to the give sink.
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func (f *fsmSnapshot) Persist(sink raft.SnapshotSink) error {
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err := func() error {
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// Write data to sink.
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if _, err := sink.Write(f.data); err != nil {
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return err
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}
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// Close the sink.
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if err := sink.Close(); err != nil {
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return err
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}
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return nil
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}()
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if err != nil {
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sink.Cancel()
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return err
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}
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return nil
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}
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// Release is a no-op.
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func (f *fsmSnapshot) Release() {}
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// readPeersJSON reads the peers from the path.
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func readPeersJSON(path string) ([]string, error) {
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b, err := ioutil.ReadFile(path)
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if err != nil && !os.IsNotExist(err) {
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return nil, err
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}
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if len(b) == 0 {
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return nil, nil
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}
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var peers []string
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dec := json.NewDecoder(bytes.NewReader(b))
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if err := dec.Decode(&peers); err != nil {
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return nil, err
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}
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return peers, nil
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}
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