//.........这里部分代码省略.........
		{
			// Range-local range contained in active range.
			keys:    [][2]string{{locPrefix("b"), loc("b")}},
			expKeys: [][2]string{{locPrefix("b"), loc("b")}},
			from:    "b", to: "c",
		},
		{
			// Mixed range-local vs global key range.
			keys: [][2]string{{loc("c"), "d\x00"}},
			from: "b", to: "e",
			err: "local key mixed with global key",
		},
		{
			// Key range touching and intersecting active range.
			keys:    [][2]string{{"a", "b"}, {"a", "c"}, {"p", "q"}, {"p", "r"}, {"a", "z"}},
			expKeys: [][2]string{{}, {"b", "c"}, {"p", "q"}, {"p", "q"}, {"b", "q"}},
			from:    "b", to: "q",
		},
		// Active key range is intersection of descriptor and [from,to).
		{
			keys:    [][2]string{{"c", "q"}},
			expKeys: [][2]string{{"d", "p"}},
			from:    "a", to: "z",
			desc: [2]string{"d", "p"},
		},
		{
			keys:    [][2]string{{"c", "q"}},
			expKeys: [][2]string{{"d", "p"}},
			from:    "d", to: "p",
			desc: [2]string{"a", "z"},
		},
	}

	for i, test := range testCases {
		goldenOriginal := roachpb.BatchRequest{}
		for _, ks := range test.keys {
			if len(ks[1]) > 0 {
				u := uuid.MakeV4()
				goldenOriginal.Add(&roachpb.ResolveIntentRangeRequest{
					Span:      roachpb.Span{Key: roachpb.Key(ks[0]), EndKey: roachpb.Key(ks[1])},
					IntentTxn: enginepb.TxnMeta{ID: &u},
				})
			} else {
				goldenOriginal.Add(&roachpb.GetRequest{
					Span: roachpb.Span{Key: roachpb.Key(ks[0])},
				})
			}
		}

		original := roachpb.BatchRequest{Requests: make([]roachpb.RequestUnion, len(goldenOriginal.Requests))}
		for i, request := range goldenOriginal.Requests {
			original.Requests[i].SetValue(request.GetInner().ShallowCopy())
		}

		desc := &roachpb.RangeDescriptor{
			StartKey: roachpb.RKey(test.desc[0]), EndKey: roachpb.RKey(test.desc[1]),
		}
		if len(desc.StartKey) == 0 {
			desc.StartKey = roachpb.RKey(test.from)
		}
		if len(desc.EndKey) == 0 {
			desc.EndKey = roachpb.RKey(test.to)
		}
		rs := roachpb.RSpan{Key: roachpb.RKey(test.from), EndKey: roachpb.RKey(test.to)}
		rs, err := rs.Intersect(desc)
		if err != nil {
			t.Errorf("%d: intersection failure: %v", i, err)
			continue
		}
		ba, num, err := truncate(original, rs)
		if err != nil || test.err != "" {
			if !testutils.IsError(err, test.err) {
				t.Errorf("%d: %v (expected: %q)", i, err, test.err)
			}
			continue
		}
		var reqs int
		for j, arg := range ba.Requests {
			req := arg.GetInner()
			if _, ok := req.(*roachpb.NoopRequest); ok {
				continue
			}
			if h := req.Header(); !bytes.Equal(h.Key, roachpb.Key(test.expKeys[j][0])) || !bytes.Equal(h.EndKey, roachpb.Key(test.expKeys[j][1])) {
				t.Errorf("%d.%d: range mismatch: actual [%q,%q), wanted [%q,%q)", i, j,
					h.Key, h.EndKey, test.expKeys[j][0], test.expKeys[j][1])
			} else if _, ok := req.(*roachpb.NoopRequest); ok != (len(h.Key) == 0) {
				t.Errorf("%d.%d: expected NoopRequest, got %T", i, j, req)
			} else if len(h.Key) != 0 {
				reqs++
			}
		}
		if reqs != num {
			t.Errorf("%d: counted %d requests, but truncation indicated %d", i, reqs, num)
		}
		if !reflect.DeepEqual(original, goldenOriginal) {
			t.Errorf("%d: truncation mutated original:\nexpected: %s\nactual: %s",
				i, goldenOriginal, original)
		}
	}
}

// truncate restricts all contained requests to the given key range
// and returns a new BatchRequest.
// All requests contained in that batch are "truncated" to the given
// span, inserting NoopRequest appropriately to replace requests which
// are left without a key range to operate on. The number of non-noop
// requests after truncation is returned.
func truncate(ba roachpb.BatchRequest, rs roachpb.RSpan) (roachpb.BatchRequest, int, error) {
	truncateOne := func(args roachpb.Request) (bool, roachpb.Span, error) {
		if _, ok := args.(*roachpb.NoopRequest); ok {
			return true, emptySpan, nil
		}
		header := args.Header()
		if !roachpb.IsRange(args) {
			// This is a point request.
			if len(header.EndKey) > 0 {
				return false, emptySpan, errors.Errorf("%T is not a range command, but EndKey is set", args)
			}
			keyAddr, err := keys.Addr(header.Key)
			if err != nil {
				return false, emptySpan, err
			}
			if !rs.ContainsKey(keyAddr) {
				return false, emptySpan, nil
			}
			return true, header, nil
		}
		// We're dealing with a range-spanning request.
		local := false
		keyAddr, err := keys.Addr(header.Key)
		if err != nil {
			return false, emptySpan, err
		}
		endKeyAddr, err := keys.Addr(header.EndKey)
		if err != nil {
			return false, emptySpan, err
		}
		if l, r := !keyAddr.Equal(header.Key), !endKeyAddr.Equal(header.EndKey); l || r {
			if !l || !r {
				return false, emptySpan, errors.Errorf("local key mixed with global key in range")
			}
			local = true
		}
		if keyAddr.Less(rs.Key) {
			// rs.Key can't be local because it contains range split points, which
			// are never local.
			if !local {
				header.Key = rs.Key.AsRawKey()
			} else {
				// The local start key should be truncated to the boundary of local keys which
				// address to rs.Key.
				header.Key = keys.MakeRangeKeyPrefix(rs.Key)
			}
		}
		if !endKeyAddr.Less(rs.EndKey) {
			// rs.EndKey can't be local because it contains range split points, which
			// are never local.
			if !local {
				header.EndKey = rs.EndKey.AsRawKey()
			} else {
				// The local end key should be truncated to the boundary of local keys which
				// address to rs.EndKey.
				header.EndKey = keys.MakeRangeKeyPrefix(rs.EndKey)
			}
		}
		// Check whether the truncation has left any keys in the range. If not,
		// we need to cut it out of the request.
		if header.Key.Compare(header.EndKey) >= 0 {
			return false, emptySpan, nil
		}
		return true, header, nil
	}

	var numNoop int
	truncBA := ba
	truncBA.Requests = make([]roachpb.RequestUnion, len(ba.Requests))
	for pos, arg := range ba.Requests {
		hasRequest, newHeader, err := truncateOne(arg.GetInner())
		if !hasRequest {
			// We omit this one, i.e. replace it with a Noop.
			numNoop++
			union := roachpb.RequestUnion{}
			union.MustSetInner(&noopRequest)
			truncBA.Requests[pos] = union
		} else {
			// Keep the old one. If we must adjust the header, must copy.
			if inner := ba.Requests[pos].GetInner(); newHeader.Equal(inner.Header()) {
				truncBA.Requests[pos] = ba.Requests[pos]
			} else {
				shallowCopy := inner.ShallowCopy()
				shallowCopy.SetHeader(newHeader)
				union := &truncBA.Requests[pos] // avoid operating on copy
				union.MustSetInner(shallowCopy)
			}
		}
		if err != nil {
			return roachpb.BatchRequest{}, 0, err
		}
	}
	return truncBA, len(ba.Requests) - numNoop, nil
}

// sendPartialBatch sends the supplied batch to the range specified by
// desc. The batch request is first truncated so that it contains only
// requests which intersect the range descriptor and keys for each
// request are limited to the range's key span. The send occurs in a
// retry loop to handle send failures. On failure to send to any
// replicas, we backoff and retry by refetching the range
// descriptor. If the underlying range seems to have split, we
// recursively invoke divideAndSendBatchToRanges to re-enumerate the
// ranges in the span and resend to each.
func (ds *DistSender) sendPartialBatch(
	ctx context.Context,
	ba roachpb.BatchRequest,
	rs roachpb.RSpan,
	desc *roachpb.RangeDescriptor,
	evictToken *EvictionToken,
	isFirst bool,
) response {
	var reply *roachpb.BatchResponse
	var pErr *roachpb.Error
	isReverse := ba.IsReverse()

	// Truncate the request to range descriptor.
	intersected, err := rs.Intersect(desc)
	if err != nil {
		return response{pErr: roachpb.NewError(err)}
	}
	truncBA, numActive, err := truncate(ba, intersected)
	if numActive == 0 && err == nil {
		// This shouldn't happen in the wild, but some tests exercise it.
		return response{
			pErr: roachpb.NewErrorf("truncation resulted in empty batch on %s: %s", intersected, ba),
		}
	}
	if err != nil {
		return response{pErr: roachpb.NewError(err)}
	}

	// Start a retry loop for sending the batch to the range.
	for r := retry.StartWithCtx(ctx, ds.rpcRetryOptions); r.Next(); {
		// If we've cleared the descriptor on a send failure, re-lookup.
		if desc == nil {
			var descKey roachpb.RKey
			if isReverse {
				descKey = intersected.EndKey
			} else {
				descKey = intersected.Key
			}
			desc, evictToken, err = ds.getDescriptor(ctx, descKey, nil, isReverse)
			if err != nil {
				log.ErrEventf(ctx, "range descriptor re-lookup failed: %s", err)
				continue
			}
		}

		reply, pErr = ds.sendSingleRange(ctx, truncBA, desc)

		// If sending succeeded, return immediately.
		if pErr == nil {
			return response{reply: reply}
		}

		log.ErrEventf(ctx, "reply error %s: %s", ba, pErr)

		// Error handling: If the error indicates that our range
		// descriptor is out of date, evict it from the cache and try
		// again. Errors that apply only to a single replica were
		// handled in send().
		//
		// TODO(bdarnell): Don't retry endlessly. If we fail twice in a
		// row and the range descriptor hasn't changed, return the error
		// to our caller.
		switch tErr := pErr.GetDetail().(type) {
		case *roachpb.SendError:
			// We've tried all the replicas without success. Either
			// they're all down, or we're using an out-of-date range
			// descriptor. Invalidate the cache and try again with the new
			// metadata.
			log.Event(ctx, "evicting range descriptor on send error and backoff for re-lookup")
			if err := evictToken.Evict(ctx); err != nil {
				return response{pErr: roachpb.NewError(err)}
			}
			// Clear the descriptor to reload on the next attempt.
			desc = nil
			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(isReverse, tErr.SuggestedRange, rs) {
					replacements = append(replacements, *tErr.SuggestedRange)
				}
//.........这里部分代码省略.........