Golang BatchRequest.ReadConsistency方法代碼示例

// RangeLookup dispatches an RangeLookup request for the given
// metadata key to the replicas of the given range. Note that we allow
// inconsistent reads when doing range lookups for efficiency. Getting
// stale data is not a correctness problem but instead may
// infrequently result in additional latency as additional range
// lookups may be required. Note also that rangeLookup bypasses the
// DistSender's Send() method, so there is no error inspection and
// retry logic here; this is not an issue since the lookup performs a
// single inconsistent read only.
func (ds *DistSender) RangeLookup(key roachpb.RKey, desc *roachpb.RangeDescriptor, considerIntents, useReverseScan bool) ([]roachpb.RangeDescriptor, *roachpb.Error) {
	ba := roachpb.BatchRequest{}
	ba.ReadConsistency = roachpb.INCONSISTENT
	ba.Add(&roachpb.RangeLookupRequest{
		Span: roachpb.Span{
			// We can interpret the RKey as a Key here since it's a metadata
			// lookup; those are never local.
			Key: key.AsRawKey(),
		},
		MaxRanges:       ds.rangeLookupMaxRanges,
		ConsiderIntents: considerIntents,
		Reverse:         useReverseScan,
	})
	replicas := newReplicaSlice(ds.gossip, desc)
	// TODO(tschottdorf) consider a Trace here, potentially that of the request
	// that had the cache miss and waits for the result.
	br, err := ds.sendRPC(nil /* Trace */, desc.RangeID, replicas, rpc.OrderRandom, ba)
	if err != nil {
		return nil, err
	}
	if br.Error != nil {
		return nil, br.Error
	}
	return br.Responses[0].GetInner().(*roachpb.RangeLookupResponse).Ranges, nil
}

// RangeLookup implements the RangeDescriptorDB interface.
// RangeLookup dispatches a RangeLookup request for the given metadata
// key to the replicas of the given range. Note that we allow
// inconsistent reads when doing range lookups for efficiency. Getting
// stale data is not a correctness problem but instead may
// infrequently result in additional latency as additional range
// lookups may be required. Note also that rangeLookup bypasses the
// DistSender's Send() method, so there is no error inspection and
// retry logic here; this is not an issue since the lookup performs a
// single inconsistent read only.
func (ds *DistSender) RangeLookup(
	key roachpb.RKey, desc *roachpb.RangeDescriptor, considerIntents, useReverseScan bool,
) ([]roachpb.RangeDescriptor, []roachpb.RangeDescriptor, *roachpb.Error) {
	ba := roachpb.BatchRequest{}
	ba.ReadConsistency = roachpb.INCONSISTENT
	ba.Add(&roachpb.RangeLookupRequest{
		Span: roachpb.Span{
			// We can interpret the RKey as a Key here since it's a metadata
			// lookup; those are never local.
			Key: key.AsRawKey(),
		},
		MaxRanges:       ds.rangeLookupMaxRanges,
		ConsiderIntents: considerIntents,
		Reverse:         useReverseScan,
	})
	replicas := newReplicaSlice(ds.gossip, desc)
	replicas.Shuffle()
	// TODO(tschottdorf): Ideally we would use the trace of the request which
	// caused this lookup.
	_ = context.TODO()
	br, err := ds.sendRPC(ds.Ctx, desc.RangeID, replicas, ba)
	if err != nil {
		return nil, nil, roachpb.NewError(err)
	}
	if br.Error != nil {
		return nil, nil, br.Error
	}
	resp := br.Responses[0].GetInner().(*roachpb.RangeLookupResponse)
	return resp.Ranges, resp.PrefetchedRanges, nil
}

// send runs the specified calls synchronously in a single batch and returns
// any errors. Returns a nil response for empty input (no requests).
func (db *DB) send(maxScanResults int64, readConsistency roachpb.ReadConsistencyType,
	reqs ...roachpb.Request) (*roachpb.BatchResponse, *roachpb.Error) {
	if len(reqs) == 0 {
		return nil, nil
	}

	if readConsistency == roachpb.INCONSISTENT {
		for _, req := range reqs {
			if req.Method() != roachpb.Get && req.Method() != roachpb.Scan &&
				req.Method() != roachpb.ReverseScan {
				return nil, roachpb.NewErrorf("method %s not allowed with INCONSISTENT batch", req.Method)
			}
		}
	}

	ba := roachpb.BatchRequest{}
	ba.Add(reqs...)

	ba.MaxScanResults = maxScanResults
	if db.userPriority != 1 {
		ba.UserPriority = db.userPriority
	}
	ba.ReadConsistency = readConsistency

	tracing.AnnotateTrace()

	br, pErr := db.sender.Send(context.TODO(), ba)
	if pErr != nil {
		if log.V(1) {
			log.Infof("failed batch: %s", pErr)
		}
		return nil, pErr
	}
	return br, nil
}

// rangeLookup dispatches an RangeLookup request for the given
// metadata key to the replicas of the given range. Note that we allow
// inconsistent reads when doing range lookups for efficiency. Getting
// stale data is not a correctness problem but instead may
// infrequently result in additional latency as additional range
// lookups may be required. Note also that rangeLookup bypasses the
// DistSender's Send() method, so there is no error inspection and
// retry logic here; this is not an issue since the lookup performs a
// single inconsistent read only.
func (ds *DistSender) rangeLookup(key roachpb.Key, options lookupOptions,
	desc *roachpb.RangeDescriptor) ([]roachpb.RangeDescriptor, error) {
	ba := roachpb.BatchRequest{}
	ba.ReadConsistency = roachpb.INCONSISTENT
	ba.Add(&roachpb.RangeLookupRequest{
		RequestHeader: roachpb.RequestHeader{
			Key:             key,
			ReadConsistency: roachpb.INCONSISTENT,
		},
		MaxRanges:       ds.rangeLookupMaxRanges,
		ConsiderIntents: options.considerIntents,
		Reverse:         options.useReverseScan,
	})
	replicas := newReplicaSlice(ds.gossip, desc)
	// TODO(tschottdorf) consider a Trace here, potentially that of the request
	// that had the cache miss and waits for the result.
	br, err := ds.sendRPC(nil /* Trace */, desc.RangeID, replicas, rpc.OrderRandom, ba)
	if err != nil {
		return nil, err
	}
	if err := br.GoError(); err != nil {
		return nil, err
	}
	return br.Responses[0].GetInner().(*roachpb.RangeLookupResponse).Ranges, nil
}

// RangeLookup dispatches an RangeLookup request for the given
// metadata key to the replicas of the given range. Note that we allow
// inconsistent reads when doing range lookups for efficiency. Getting
// stale data is not a correctness problem but instead may
// infrequently result in additional latency as additional range
// lookups may be required. Note also that rangeLookup bypasses the
// DistSender's Send() method, so there is no error inspection and
// retry logic here; this is not an issue since the lookup performs a
// single inconsistent read only.
func (ds *DistSender) RangeLookup(key roachpb.RKey, desc *roachpb.RangeDescriptor, considerIntents, useReverseScan bool) ([]roachpb.RangeDescriptor, *roachpb.Error) {
	ba := roachpb.BatchRequest{}
	ba.ReadConsistency = roachpb.INCONSISTENT
	ba.Add(&roachpb.RangeLookupRequest{
		Span: roachpb.Span{
			// We can interpret the RKey as a Key here since it's a metadata
			// lookup; those are never local.
			Key: key.AsRawKey(),
		},
		MaxRanges:       ds.rangeLookupMaxRanges,
		ConsiderIntents: considerIntents,
		Reverse:         useReverseScan,
	})
	replicas := newReplicaSlice(ds.gossip, desc)
	trace := ds.Tracer.StartSpan("range lookup")
	defer trace.Finish()
	// TODO(tschottdorf): Ideally we would use the trace of the request which
	// caused this lookup instead of a new one.
	br, err := ds.sendRPC(trace, desc.RangeID, replicas, orderRandom, ba)
	if err != nil {
		return nil, err
	}
	if br.Error != nil {
		return nil, br.Error
	}
	return br.Responses[0].GetInner().(*roachpb.RangeLookupResponse).Ranges, nil
}

// rangeLookup implements the rangeDescriptorDB interface. It looks up
// the descriptors for the given (meta) key.
func (ls *LocalSender) rangeLookup(key roachpb.Key, options lookupOptions, _ *roachpb.RangeDescriptor) ([]roachpb.RangeDescriptor, error) {
	ba := roachpb.BatchRequest{}
	ba.ReadConsistency = roachpb.INCONSISTENT
	ba.Add(&roachpb.RangeLookupRequest{
		RequestHeader: roachpb.RequestHeader{
			Key: key,
		},
		MaxRanges:       1,
		ConsiderIntents: options.considerIntents,
		Reverse:         options.useReverseScan,
	})
	br, pErr := ls.Send(context.Background(), ba)
	if pErr != nil {
		return nil, pErr.GoError()
	}
	return br.Responses[0].GetInner().(*roachpb.RangeLookupResponse).Ranges, nil
}

// RangeLookup implements the RangeDescriptorDB interface. It looks up
// the descriptors for the given (meta) key.
func (ls *Stores) RangeLookup(key roachpb.RKey, _ *roachpb.RangeDescriptor, considerIntents, useReverseScan bool) ([]roachpb.RangeDescriptor, *roachpb.Error) {
	ba := roachpb.BatchRequest{}
	ba.ReadConsistency = roachpb.INCONSISTENT
	ba.Add(&roachpb.RangeLookupRequest{
		Span: roachpb.Span{
			// key is a meta key, so it's guaranteed not local-prefixed.
			Key: key.AsRawKey(),
		},
		MaxRanges:       1,
		ConsiderIntents: considerIntents,
		Reverse:         useReverseScan,
	})
	br, pErr := ls.Send(context.Background(), ba)
	if pErr != nil {
		return nil, pErr
	}
	return br.Responses[0].GetInner().(*roachpb.RangeLookupResponse).Ranges, nil
}