// GetRange fetches a range by ID. Returns an error if no range is found.
func (s *Store) GetRange(rangeID int64) (*Range, error) {
s.mu.RLock()
defer s.mu.RUnlock()
if rng, ok := s.ranges[rangeID]; ok {
return rng, nil
}
return nil, proto.NewRangeNotFoundError(rangeID)
}
// addWriteCmd first consults the response cache to determine whether
// this command has already been sent to the range. If a response is
// found, it's returned immediately and not submitted to raft. Next,
// the timestamp cache is checked to determine if any newer accesses to
// this command's affected keys have been made. If so, this command's
// timestamp is moved forward. Finally the keys affected by this
// command are added as pending writes to the read queue and the
// command is submitted to Raft. Upon completion, the write is removed
// from the read queue and the reply is added to the response cache.
// If wait is true, will block until the command is complete.
func (r *Range) addWriteCmd(ctx context.Context, args proto.Request, reply proto.Response, wait bool) error {
// Check the response cache in case this is a replay. This call
// may block if the same command is already underway.
header := args.Header()
// Add the write to the command queue to gate subsequent overlapping
// Commands until this command completes. Note that this must be
// done before getting the max timestamp for the key(s), as
// timestamp cache is only updated after preceding commands have
// been run to successful completion.
cmdKey := r.beginCmd(header, false)
// This replica must have leader lease to process a write.
if err := r.redirectOnOrAcquireLeaderLease(header.Timestamp); err != nil {
r.endCmd(cmdKey, args, err, false /* !readOnly */)
reply.Header().SetGoError(err)
return err
}
// Two important invariants of Cockroach: 1) encountering a more
// recently written value means transaction restart. 2) values must
// be written with a greater timestamp than the most recent read to
// the same key. Check the timestamp cache for reads/writes which
// are at least as recent as the timestamp of this write. For
// writes, send WriteTooOldError; for reads, update the write's
// timestamp. When the write returns, the updated timestamp will
// inform the final commit timestamp.
if usesTimestampCache(args) {
r.Lock()
rTS, wTS := r.tsCache.GetMax(header.Key, header.EndKey, header.Txn.GetID())
r.Unlock()
// Always push the timestamp forward if there's been a read which
// occurred after our txn timestamp.
if !rTS.Less(header.Timestamp) {
header.Timestamp = rTS.Next()
}
// If there's a newer write timestamp...
if !wTS.Less(header.Timestamp) {
// If we're in a txn, set a write too old error in reply. We
// still go ahead and try the write because we want to avoid
// restarting the transaction in the event that there isn't an
// intent or the intent can be pushed by us.
if header.Txn != nil {
err := &proto.WriteTooOldError{Timestamp: header.Timestamp, ExistingTimestamp: wTS}
reply.Header().SetGoError(err)
} else {
// Otherwise, make sure we advance the request's timestamp.
header.Timestamp = wTS.Next()
}
}
}
errChan, pendingCmd := r.proposeRaftCommand(ctx, args, reply)
// Create a completion func for mandatory cleanups which we either
// run synchronously if we're waiting or in a goroutine otherwise.
completionFunc := func() error {
// First wait for raft to commit or abort the command.
var err error
if err = <-errChan; err == nil {
// Next if the command was committed, wait for the range to apply it.
err = <-pendingCmd.done
} else if err == multiraft.ErrGroupDeleted {
// This error needs to be converted appropriately so that
// clients will retry.
err = proto.NewRangeNotFoundError(r.Desc().RaftID)
}
// As for reads, update timestamp cache with the timestamp
// of this write on success. This ensures a strictly higher
// timestamp for successive writes to the same key or key range.
r.endCmd(cmdKey, args, err, false /* !readOnly */)
return err
}
if wait {
return completionFunc()
}
go func() {
// If the original client didn't wait (e.g. resolve write intent),
// log execution errors so they're surfaced somewhere.
if err := completionFunc(); err != nil {
// TODO(tschottdorf): possible security risk to log args.
log.Warningc(ctx, "async execution of %v failed: %s", args, err)
}
}()
return nil
}
// addWriteCmd first adds the keys affected by this command as pending writes
// to the command queue. Next, the timestamp cache is checked to determine if
// any newer accesses to this command's affected keys have been made. If so,
// the command's timestamp is moved forward. Finally, the command is submitted
// to Raft. Upon completion, the write is removed from the read queue and any
// error returned. If a WaitGroup is supplied, it is signaled when the command
// enters Raft or the function returns with a preprocessing error, whichever
// happens earlier.
func (r *Range) addWriteCmd(ctx context.Context, args proto.Request, wg *sync.WaitGroup) (proto.Response, error) {
signal := func() {
if wg != nil {
wg.Done()
wg = nil
}
}
// This happens more eagerly below, but it's important to guarantee that
// early returns do not skip this.
defer signal()
header := args.Header()
if err := r.checkCmdHeader(args.Header()); err != nil {
return nil, err
}
trace := tracer.FromCtx(ctx)
// Add the write to the command queue to gate subsequent overlapping
// Commands until this command completes. Note that this must be
// done before getting the max timestamp for the key(s), as
// timestamp cache is only updated after preceding commands have
// been run to successful completion.
qDone := trace.Epoch("command queue")
cmdKey := r.beginCmd(header, false)
qDone()
// This replica must have leader lease to process a write.
if err := r.redirectOnOrAcquireLeaderLease(trace, header.Timestamp); err != nil {
r.endCmd(cmdKey, args, err, false /* !readOnly */)
return nil, err
}
// Two important invariants of Cockroach: 1) encountering a more
// recently written value means transaction restart. 2) values must
// be written with a greater timestamp than the most recent read to
// the same key. Check the timestamp cache for reads/writes which
// are at least as recent as the timestamp of this write. For
// writes, send WriteTooOldError; for reads, update the write's
// timestamp. When the write returns, the updated timestamp will
// inform the final commit timestamp.
if usesTimestampCache(args) {
r.Lock()
rTS, wTS := r.tsCache.GetMax(header.Key, header.EndKey, header.Txn.GetID())
r.Unlock()
// Always push the timestamp forward if there's been a read which
// occurred after our txn timestamp.
if !rTS.Less(header.Timestamp) {
header.Timestamp = rTS.Next()
}
// If there's a newer write timestamp...
if !wTS.Less(header.Timestamp) {
// If we're in a txn, we still go ahead and try the write since
// we want to avoid restarting the transaction in the event that
// there isn't an intent or the intent can be pushed by us.
//
// If we're not in a txn, it's trivial to just advance our timestamp.
if header.Txn == nil {
header.Timestamp = wTS.Next()
}
}
}
defer trace.Epoch("raft")()
errChan, pendingCmd := r.proposeRaftCommand(ctx, args)
signal()
// First wait for raft to commit or abort the command.
var err error
var reply proto.Response
if err = <-errChan; err == nil {
// Next if the command was committed, wait for the range to apply it.
respWithErr := <-pendingCmd.done
reply, err = respWithErr.reply, respWithErr.err
} else if err == multiraft.ErrGroupDeleted {
// This error needs to be converted appropriately so that
// clients will retry.
err = proto.NewRangeNotFoundError(r.Desc().RaftID)
}
// As for reads, update timestamp cache with the timestamp
// of this write on success. This ensures a strictly higher
// timestamp for successive writes to the same key or key range.
r.endCmd(cmdKey, args, err, false /* !readOnly */)
return reply, err
}
