// sendChunk is in charge of sending an "admissible" piece of batch, i.e. one
// which doesn't need to be subdivided further before going to a range (so no
// mixing of forward and reverse scans, etc).
func (ds *DistSender) sendChunk(ctx context.Context, ba proto.BatchRequest) (*proto.BatchResponse, error) {
// TODO(tschottdorf): prepare for removing Key and EndKey from BatchRequest,
// making sure that anything that relies on them goes bust.
ba.Key, ba.EndKey = nil, nil
isReverse := ba.IsReverse()
trace := tracer.FromCtx(ctx)
// The minimal key range encompassing all requests contained within.
// Local addressing has already been resolved.
// TODO(tschottdorf): consider rudimentary validation of the batch here
// (for example, non-range requests with EndKey, or empty key ranges).
from, to := keys.Range(ba)
var br *proto.BatchResponse
// Send the request to one range per iteration.
for {
options := lookupOptions{
useReverseScan: isReverse,
}
var curReply *proto.BatchResponse
var desc *proto.RangeDescriptor
var needAnother bool
var err error
for r := retry.Start(ds.rpcRetryOptions); r.Next(); {
// Get range descriptor (or, when spanning range, descriptors). Our
// error handling below may clear them on certain errors, so we
// refresh (likely from the cache) on every retry.
descDone := trace.Epoch("meta descriptor lookup")
var evictDesc func()
desc, needAnother, evictDesc, err = ds.getDescriptors(from, to, options)
descDone()
// getDescriptors may fail retryably if the first range isn't
// available via Gossip.
if err != nil {
if rErr, ok := err.(retry.Retryable); ok && rErr.CanRetry() {
if log.V(1) {
log.Warning(err)
}
continue
}
break
}
// If there's no transaction and op spans ranges, possibly
// re-run as part of a transaction for consistency. The
// case where we don't need to re-run is if the read
// consistency is not required.
if needAnother && ba.Txn == nil && ba.IsRange() &&
ba.ReadConsistency != proto.INCONSISTENT {
return nil, &proto.OpRequiresTxnError{}
}
// It's possible that the returned descriptor misses parts of the
// keys it's supposed to scan after it's truncated to match the
// descriptor. Example revscan [a,g), first desc lookup for "g"
// returns descriptor [c,d) -> [d,g) is never scanned.
// We evict and retry in such a case.
if (isReverse && !desc.ContainsKeyRange(desc.StartKey, to)) || (!isReverse && !desc.ContainsKeyRange(from, desc.EndKey)) {
evictDesc()
continue
}
curReply, err = func() (*proto.BatchResponse, error) {
// Truncate the request to our current key range.
untruncate, numActive, trErr := truncate(&ba, desc, from, to)
if numActive == 0 {
untruncate()
// This shouldn't happen in the wild, but some tests
// exercise it.
return nil, util.Errorf("truncation resulted in empty batch on [%s,%s): %s",
from, to, ba)
}
defer untruncate()
if trErr != nil {
return nil, trErr
}
// TODO(tschottdorf): make key range on batch redundant. The
// requests within dictate it anyways.
ba.Key, ba.EndKey = keys.Range(ba)
reply, err := ds.sendAttempt(trace, ba, desc)
ba.Key, ba.EndKey = nil, nil
if err != nil {
if log.V(0 /* TODO(tschottdorf): 1 */) {
log.Warningf("failed to invoke %s: %s", ba, err)
}
}
return reply, err
}()
// If sending succeeded, break this loop.
if err == nil {
break
}
// Error handling below.
// If retryable, allow retry. For range not found or range
// key mismatch errors, we don't backoff on the retry,
// but reset the backoff loop so we can retry immediately.
switch tErr := err.(type) {
case *rpc.SendError:
// For an RPC error to occur, we must've been unable to contact
// any replicas. In this case, likely all nodes are down (or
// not getting back to us within a reasonable amount of time).
// We may simply not be trying to talk to the up-to-date
// replicas, so clearing the descriptor here should be a good
// idea.
// TODO(tschottdorf): If a replica group goes dead, this
// will cause clients to put high read pressure on the first
// range, so there should be some rate limiting here.
evictDesc()
if tErr.CanRetry() {
continue
}
case *proto.RangeNotFoundError, *proto.RangeKeyMismatchError:
trace.Event(fmt.Sprintf("reply error: %T", err))
// Range descriptor might be out of date - evict it.
evictDesc()
// On addressing errors, don't backoff; retry immediately.
r.Reset()
if log.V(1) {
log.Warning(err)
}
// For the remainder of this call, we'll assume that intents
// are fair game. This replaces more complex logic based on
// the type of request.
options.considerIntents = true
continue
case *proto.NotLeaderError:
trace.Event(fmt.Sprintf("reply error: %T", err))
newLeader := tErr.GetLeader()
// Verify that leader is a known replica according to the
// descriptor. If not, we've got a stale replica; evict cache.
// Next, cache the new leader.
if newLeader != nil {
if i, _ := desc.FindReplica(newLeader.StoreID); i == -1 {
if log.V(1) {
log.Infof("error indicates unknown leader %s, expunging descriptor %s", newLeader, desc)
}
evictDesc()
}
} else {
newLeader = &proto.Replica{}
}
ds.updateLeaderCache(proto.RangeID(desc.RangeID), *newLeader)
if log.V(1) {
log.Warning(err)
}
r.Reset()
continue
case retry.Retryable:
if tErr.CanRetry() {
if log.V(1) {
log.Warning(err)
}
trace.Event(fmt.Sprintf("reply error: %T", err))
continue
}
}
break
}
// Immediately return if querying a range failed non-retryably.
if err != nil {
return nil, err
}
first := br == nil
if first {
// First response from a Range.
br = curReply
} else {
// This was the second or later call in a cross-Range request.
// Combine the new response with the existing one.
if err := br.Combine(curReply); err != nil {
panic(err)
// TODO(tschottdorf): return nil, err
}
}
// If this request has a bound (such as MaxResults in
// ScanRequest) and we are going to query at least one more range,
// check whether enough rows have been retrieved.
// TODO(tschottdorf): need tests for executing a multi-range batch
// with various bounded requests which saturate at different times.
if needAnother {
// Start with the assumption that all requests are saturated.
// Below, we look at each and decide whether that's true.
// Everything that is indeed saturated is "masked out" from the
// batch request; only if that's all requests does needAnother
// remain false.
needAnother = false
if first {
// Clone ba.Requests. This is because we're multi-range, and
// some requests may be bounded, which could lead to them being
// masked out once they're saturated. We don't want to risk
// removing requests that way in the "master copy" since that
// could lead to omitting requests in certain retry scenarios.
ba.Requests = append([]proto.RequestUnion(nil), ba.Requests...)
}
for i, union := range ba.Requests {
args := union.GetValue()
if _, ok := args.(*proto.NoopRequest); ok {
// NoopRequests are skipped.
continue
}
boundedArg, ok := args.(proto.Bounded)
if !ok {
// Non-bounded request. We will have to query all ranges.
needAnother = true
continue
}
prevBound := boundedArg.GetBound()
cReply, ok := curReply.Responses[i].GetValue().(proto.Countable)
if !ok || prevBound <= 0 {
// Request bounded, but without max results. Again, will
// need to query everything we can. The case in which the reply
// isn't countable occurs when the request wasn't active for
// that range (since it didn't apply to it), so the response
// is a NoopResponse.
needAnother = true
continue
}
nextBound := prevBound - cReply.Count()
if nextBound <= 0 {
// We've hit max results for this piece of the batch. Mask
// it out (we've copied the requests slice above, so this
// is kosher).
ba.Requests[i].Reset() // necessary (no one-of?)
if !ba.Requests[i].SetValue(&proto.NoopRequest{}) {
panic("RequestUnion excludes NoopRequest")
}
continue
}
// The request isn't saturated yet.
needAnother = true
boundedArg.SetBound(nextBound)
}
}
// If this was the last range accessed by this call, exit loop.
if !needAnother {
return br, nil
}
if isReverse {
// In next iteration, query previous range.
// We use the StartKey of the current descriptor as opposed to the
// EndKey of the previous one since that doesn't have bugs when
// stale descriptors come into play.
to = prev(ba, desc.StartKey)
} else {
// In next iteration, query next range.
// It's important that we use the EndKey of the current descriptor
// as opposed to the StartKey of the next one: if the former is stale,
// it's possible that the next range has since merged the subsequent
// one, and unless both descriptors are stale, the next descriptor's
// StartKey would move us to the beginning of the current range,
// resulting in a duplicate scan.
from = next(ba, desc.EndKey)
}
trace.Event("querying next range")
}
}