// 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). The parameters and return values
// correspond to client.Sender with the exception of the returned boolean,
// which is true when indicating that the caller should retry but needs to send
// EndTransaction in a separate request.
func (ds *DistSender) sendChunk(ctx context.Context, ba roachpb.BatchRequest) (*roachpb.BatchResponse, *roachpb.Error, bool) {
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).
rs := keys.Range(ba)
var br *roachpb.BatchResponse
// Send the request to one range per iteration.
for {
considerIntents := false
var curReply *roachpb.BatchResponse
var desc *roachpb.RangeDescriptor
var needAnother bool
var pErr *roachpb.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, pErr = ds.getDescriptors(rs, considerIntents, isReverse)
descDone()
// getDescriptors may fail retryably if the first range isn't
// available via Gossip.
if pErr != nil {
if pErr.Retryable {
if log.V(1) {
log.Warning(pErr)
}
continue
}
break
}
if needAnother && br == nil {
// TODO(tschottdorf): we should have a mechanism for discovering
// range merges (descriptor staleness will mostly go unnoticed),
// or we'll be turning single-range queries into multi-range
// queries for no good reason.
// 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 ba.Txn == nil && ba.IsPossibleTransaction() &&
ba.ReadConsistency != roachpb.INCONSISTENT {
return nil, roachpb.NewError(&roachpb.OpRequiresTxnError{}), false
}
// If the request is more than but ends with EndTransaction, we
// want the caller to come again with the EndTransaction in an
// extra call.
if l := len(ba.Requests) - 1; l > 0 && ba.Requests[l].GetInner().Method() == roachpb.EndTransaction {
return nil, roachpb.NewError(errors.New("cannot send 1PC txn to multiple ranges")), true /* shouldSplitET */
}
}
// 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, rs.EndKey)) || (!isReverse && !desc.ContainsKeyRange(rs.Key, desc.EndKey)) {
evictDesc()
continue
}
curReply, pErr = func() (*roachpb.BatchResponse, *roachpb.Error) {
// Truncate the request to our current key range.
intersected, iErr := rs.Intersect(desc)
if iErr != nil {
return nil, roachpb.NewError(iErr)
}
truncBA, numActive, trErr := truncate(ba, intersected)
if numActive == 0 && trErr == nil {
// This shouldn't happen in the wild, but some tests
// exercise it.
return nil, roachpb.NewErrorf("truncation resulted in empty batch on [%s,%s): %s",
rs.Key, rs.EndKey, ba)
}
if trErr != nil {
return nil, roachpb.NewError(trErr)
}
return ds.sendSingleRange(trace, truncBA, desc)
}()
// If sending succeeded, break this loop.
if pErr == nil {
break
}
if log.V(1) {
log.Warningf("failed to invoke %s: %s", ba, pErr)
}
trace.Event(fmt.Sprintf("reply error: %T", pErr.GoError()))
// 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 := pErr.GoError().(type) {
case *roachpb.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 *roachpb.RangeNotFoundError, *roachpb.RangeKeyMismatchError:
// 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(tErr)
}
// On retries, allow [uncommitted] intents on range descriptor
// lookups to be returned 50% of the time in order to succeed
// at finding the transaction record pointed to by the intent
// itself. The 50% probability of returning either the current
// intent or the previously committed value balances between
// the two cases where the intent's txn hasn't yet been
// committed (the previous value is correct), or the intent's
// txn has been committed (the intent value is correct).
considerIntents = true
continue
case *roachpb.NotLeaderError:
newLeader := tErr.Leader
// 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 = &roachpb.ReplicaDescriptor{}
}
ds.updateLeaderCache(roachpb.RangeID(desc.RangeID), *newLeader)
if log.V(1) {
log.Warning(tErr)
}
r.Reset()
continue
case retry.Retryable:
if tErr.CanRetry() {
if log.V(1) {
log.Warning(tErr)
}
continue
}
}
break
}
// Immediately return if querying a range failed non-retryably.
if pErr != nil {
return nil, pErr, false
}
ba.Txn.Update(curReply.Txn)
if br == nil {
// 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 {
return nil, roachpb.NewError(err), false
}
}
// 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 br == nil {
// 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([]roachpb.RequestUnion(nil), ba.Requests...)
}
for i, union := range ba.Requests {
args := union.GetInner()
if _, ok := args.(*roachpb.NoopRequest); ok {
// NoopRequests are skipped.
continue
}
boundedArg, ok := args.(roachpb.Bounded)
if !ok {
// Non-bounded request. We will have to query all ranges.
needAnother = true
continue
}
prevBound := boundedArg.GetBound()
cReply, ok := curReply.Responses[i].GetInner().(roachpb.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(&roachpb.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, false
}
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.
rs.EndKey = 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.
rs.Key = next(ba, desc.EndKey)
}
trace.Event("querying next range")
}
}
// 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). The parameters and return values
// correspond to client.Sender with the exception of the returned boolean,
// which is true when indicating that the caller should retry but needs to send
// EndTransaction in a separate request.
func (ds *DistSender) sendChunk(ctx context.Context, ba roachpb.BatchRequest) (*roachpb.BatchResponse, *roachpb.Error, bool) {
isReverse := ba.IsReverse()
ctx, cleanup := tracing.EnsureContext(ctx, ds.Tracer)
defer cleanup()
// 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).
rs, err := keys.Range(ba)
if err != nil {
return nil, roachpb.NewError(err), false
}
var br *roachpb.BatchResponse
// Send the request to one range per iteration.
for {
// Increase the sequence counter only once before sending RPCs to
// the ranges involved in this chunk of the batch (as opposed to for
// each RPC individually). On RPC errors, there's no guarantee that
// the request hasn't made its way to the target regardless of the
// error; we'd like the second execution to be caught by the sequence
// cache if that happens. There is a small chance that that we address
// a range twice in this chunk (stale/suboptimal descriptors due to
// splits/merges) which leads to a transaction retry.
// TODO(tschottdorf): it's possible that if we don't evict from the
// cache we could be in for a busy loop.
ba.SetNewRequest()
var curReply *roachpb.BatchResponse
var desc *roachpb.RangeDescriptor
var evictToken evictionToken
var needAnother bool
var pErr *roachpb.Error
var finished bool
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.
log.Trace(ctx, "meta descriptor lookup")
desc, needAnother, evictToken, pErr = ds.getDescriptors(rs, evictToken, isReverse)
// getDescriptors may fail retryably if the first range isn't
// available via Gossip.
if pErr != nil {
log.Trace(ctx, "range descriptor lookup failed: "+pErr.String())
if pErr.Retryable {
if log.V(1) {
log.Warning(pErr)
}
continue
}
break
} else {
log.Trace(ctx, "looked up range descriptor")
}
if needAnother && br == nil {
// TODO(tschottdorf): we should have a mechanism for discovering
// range merges (descriptor staleness will mostly go unnoticed),
// or we'll be turning single-range queries into multi-range
// queries for no good reason.
// 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 ba.Txn == nil && ba.IsPossibleTransaction() &&
ba.ReadConsistency != roachpb.INCONSISTENT {
return nil, roachpb.NewError(&roachpb.OpRequiresTxnError{}), false
}
// If the request is more than but ends with EndTransaction, we
// want the caller to come again with the EndTransaction in an
// extra call.
if l := len(ba.Requests) - 1; l > 0 && ba.Requests[l].GetInner().Method() == roachpb.EndTransaction {
return nil, roachpb.NewError(errors.New("cannot send 1PC txn to multiple ranges")), true /* shouldSplitET */
}
}
// 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.
includesFrontOfCurSpan := func(rd *roachpb.RangeDescriptor) bool {
if isReverse {
// This approach is needed because rs.EndKey is exclusive.
return desc.ContainsKeyRange(desc.StartKey, rs.EndKey)
}
return desc.ContainsKey(rs.Key)
}
if !includesFrontOfCurSpan(desc) {
if err := evictToken.Evict(); err != nil {
return nil, roachpb.NewError(err), false
}
// On addressing errors, don't backoff; retry immediately.
r.Reset()
continue
}
curReply, pErr = func() (*roachpb.BatchResponse, *roachpb.Error) {
// Truncate the request to our current key range.
intersected, iErr := rs.Intersect(desc)
if iErr != nil {
return nil, roachpb.NewError(iErr)
}
truncBA, numActive, trErr := truncate(ba, intersected)
if numActive == 0 && trErr == nil {
// This shouldn't happen in the wild, but some tests
// exercise it.
return nil, roachpb.NewErrorf("truncation resulted in empty batch on [%s,%s): %s",
rs.Key, rs.EndKey, ba)
}
if trErr != nil {
return nil, roachpb.NewError(trErr)
}
return ds.sendSingleRange(ctx, truncBA, desc)
}()
// If sending succeeded, break this loop.
if pErr == nil {
finished = true
break
}
if log.V(1) {
log.Warningf("failed to invoke %s: %s", ba, pErr)
}
log.Trace(ctx, fmt.Sprintf("reply error: %T", pErr.GetDetail()))
// 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 := pErr.GetDetail().(type) {
case *roachpb.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.
if err := evictToken.Evict(); err != nil {
return nil, roachpb.NewError(err), false
}
if tErr.CanRetry() {
continue
}
case *roachpb.RangeNotFoundError:
// Range descriptor might be out of date - evict it. This is
// likely the result of a rebalance.
if err := evictToken.Evict(); err != nil {
return nil, roachpb.NewError(err), false
}
// On addressing errors, don't backoff; retry immediately.
r.Reset()
if log.V(1) {
log.Warning(tErr)
}
continue
case *roachpb.RangeKeyMismatchError:
// Range descriptor might be out of date - evict it. This is
// likely the result of a range split. If we have new range
// descriptors, insert them instead as long as they are different
// from the last descriptor to avoid endless loops.
var replacements []roachpb.RangeDescriptor
different := func(rd *roachpb.RangeDescriptor) bool {
return !desc.RSpan().Equal(rd.RSpan())
}
if tErr.MismatchedRange != nil && different(tErr.MismatchedRange) {
replacements = append(replacements, *tErr.MismatchedRange)
}
if tErr.SuggestedRange != nil && different(tErr.SuggestedRange) {
if includesFrontOfCurSpan(tErr.SuggestedRange) {
replacements = append(replacements, *tErr.SuggestedRange)
}
}
// Same as Evict() if replacements is empty.
if err := evictToken.EvictAndReplace(replacements...); err != nil {
return nil, roachpb.NewError(err), false
}
// On addressing errors, don't backoff; retry immediately.
r.Reset()
if log.V(1) {
log.Warning(tErr)
}
continue
case *roachpb.NotLeaderError:
newLeader := tErr.Leader
if newLeader != nil {
// Verify that leader is a known replica according to the
// descriptor. If not, we've got a stale range descriptor;
// evict cache.
if i, _ := desc.FindReplica(newLeader.StoreID); i == -1 {
if log.V(1) {
log.Infof("error indicates unknown leader %s, expunging descriptor %s", newLeader, desc)
}
if err := evictToken.Evict(); err != nil {
return nil, roachpb.NewError(err), false
}
}
} else {
// If the new leader is unknown, we were talking to a
// replica that is partitioned away from the majority. Our
// range descriptor may be stale, so clear the cache.
//
// TODO(bdarnell): An unknown-leader error doesn't
// necessarily mean our descriptor is stale. Ideally we
// would treat these errors more like SendError: retry on
// another node (at a lower level), and then if it reaches
// this level then we know we've exhausted our options and
// must clear the cache.
if err := evictToken.Evict(); err != nil {
return nil, roachpb.NewError(err), false
}
newLeader = &roachpb.ReplicaDescriptor{}
}
// Next, cache the new leader.
ds.updateLeaderCache(roachpb.RangeID(desc.RangeID), *newLeader)
if log.V(1) {
log.Warning(tErr)
}
r.Reset()
continue
case retry.Retryable:
if tErr.CanRetry() {
if log.V(1) {
log.Warning(tErr)
}
continue
}
}
break
}
// Immediately return if querying a range failed non-retryably.
if pErr != nil {
return nil, pErr, false
} else if !finished {
select {
case <-ds.rpcRetryOptions.Closer:
return nil, roachpb.NewError(&roachpb.NodeUnavailableError{}), false
default:
log.Fatal("exited retry loop with nil error but finished=false")
}
}
ba.Txn.Update(curReply.Txn)
if br == nil {
// 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 {
return nil, roachpb.NewError(err), false
}
}
if ba.MaxScanResults > 0 {
// Count how many results we received.
var numResults int64
for _, resp := range curReply.Responses {
if cResp, ok := resp.GetInner().(roachpb.Countable); ok {
numResults += cResp.Count()
}
}
if numResults > ba.MaxScanResults {
panic(fmt.Sprintf("received %d results, limit was %d", numResults, ba.MaxScanResults))
}
ba.MaxScanResults -= numResults
if ba.MaxScanResults == 0 {
// We are done with this batch. Some requests might have NoopResponses; we must
// replace them with empty responses of the proper type.
for i, req := range ba.Requests {
if _, ok := br.Responses[i].GetInner().(*roachpb.NoopResponse); !ok {
continue
}
union := roachpb.ResponseUnion{}
var reply roachpb.Response
if _, ok := req.GetInner().(*roachpb.ScanRequest); ok {
reply = &roachpb.ScanResponse{}
} else {
_ = req.GetInner().(*roachpb.ReverseScanRequest)
reply = &roachpb.ReverseScanResponse{}
}
union.MustSetInner(reply)
br.Responses[i] = union
}
return br, nil, false
}
}
// 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 br == nil {
// 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([]roachpb.RequestUnion(nil), ba.Requests...)
}
for i, union := range ba.Requests {
args := union.GetInner()
if _, ok := args.(*roachpb.NoopRequest); ok {
// NoopRequests are skipped.
continue
}
boundedArg, ok := args.(roachpb.Bounded)
if !ok {
// Non-bounded request. We will have to query all ranges.
needAnother = true
continue
}
prevBound := boundedArg.GetBound()
cReply, ok := curReply.Responses[i].GetInner().(roachpb.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).
union := &ba.Requests[i] // avoid working on copy
union.MustSetInner(&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, false
}
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.
rs.EndKey, err = 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.
rs.Key, err = next(ba, desc.EndKey)
}
if err != nil {
return nil, roachpb.NewError(err), false
}
log.Trace(ctx, "querying next range")
}
}