Golang Key.ShallowNext方法代碼示例

// addKeyRange adds the specified key range to the range group,
// taking care not to add this range if existing entries already
// completely cover the range.
func addKeyRange(keys interval.RangeGroup, start, end roachpb.Key) {
	// This gives us a memory-efficient end key if end is empty.
	// The most common case for keys in the intents interval map
	// is for single keys. However, the range group requires
	// a non-empty interval, so we create two key slices which
	// share the same underlying byte array.
	if len(end) == 0 {
		end = start.ShallowNext()
		start = end[:len(start)]
	}
	keyR := interval.Range{
		Start: interval.Comparable(start),
		End:   interval.Comparable(end),
	}
	keys.Add(keyR)
}

func (tc *TimestampCache) getMax(start, end roachpb.Key, txnID *uuid.UUID, readTSCache bool) roachpb.Timestamp {
	if len(end) == 0 {
		end = start.ShallowNext()
	}
	max := tc.lowWater
	cache := tc.wCache
	if readTSCache {
		cache = tc.rCache
	}
	for _, o := range cache.GetOverlaps(start, end) {
		ce := o.Value.(*cacheValue)
		if ce.txnID == nil || txnID == nil || !roachpb.TxnIDEqual(txnID, ce.txnID) {
			if max.Less(ce.timestamp) {
				max = ce.timestamp
			}
		}
	}
	return max
}

// Add the specified timestamp to the cache as covering the range of
// keys from start to end. If end is nil, the range covers the start
// key only. txnID is nil for no transaction. readTSCache specifies
// whether the command adding this timestamp should update the read
// timestamp; false to update the write timestamp cache.
func (tc *TimestampCache) Add(start, end roachpb.Key, timestamp roachpb.Timestamp, txnID *uuid.UUID, readTSCache bool) {
	// This gives us a memory-efficient end key if end is empty.
	if len(end) == 0 {
		end = start.ShallowNext()
		start = end[:len(start)]
	}
	if tc.latest.Less(timestamp) {
		tc.latest = timestamp
	}
	// Only add to the cache if the timestamp is more recent than the
	// low water mark.
	if tc.lowWater.Less(timestamp) {
		cache := tc.wCache
		if readTSCache {
			cache = tc.rCache
		}

		addRange := func(r interval.Range) {
			value := cacheValue{timestamp: timestamp, txnID: txnID}
			key := cache.MakeKey(r.Start, r.End)
			entry := makeCacheEntry(key, value)
			cache.AddEntry(entry)
		}
		r := interval.Range{
			Start: interval.Comparable(start),
			End:   interval.Comparable(end),
		}

		// Check existing, overlapping entries and truncate/split/remove if
		// superseded and in the past. If existing entries are in the future,
		// subtract from the range/ranges that need to be added to cache.
		for _, o := range cache.GetOverlaps(r.Start, r.End) {
			cv := o.Value.(*cacheValue)
			sCmp := r.Start.Compare(o.Key.Start)
			eCmp := r.End.Compare(o.Key.End)
			if !timestamp.Less(cv.timestamp) {
				// The existing interval has a timestamp less than or equal to the new interval.
				// Compare interval ranges to determine how to modify existing interval.
				switch {
				case sCmp == 0 && eCmp == 0:
					// New and old are equal; replace old with new and avoid the need to insert new.
					//
					// New: ------------
					// Old: ------------
					//
					// New: ------------
					*cv = cacheValue{timestamp: timestamp, txnID: txnID}
					cache.MoveToEnd(o.Entry)
					return
				case sCmp <= 0 && eCmp >= 0:
					// New contains or is equal to old; delete old.
					//
					// New: ------------      ------------      ------------
					// Old:   --------    or    ----------  or  ----------
					//
					// Old:
					cache.DelEntry(o.Entry)
				case sCmp > 0 && eCmp < 0:
					// Old contains new; split up old into two.
					//
					// New:     ----
					// Old: ------------
					//
					// Old: ----    ----
					oldEnd := o.Key.End
					o.Key.End = r.Start

					key := cache.MakeKey(r.End, oldEnd)
					entry := makeCacheEntry(key, *cv)
					cache.AddEntryAfter(entry, o.Entry)
				case eCmp >= 0:
					// Left partial overlap; truncate old end.
					//
					// New:     --------          --------
					// Old: --------      or  ------------
					//
					// Old: ----              ----
					o.Key.End = r.Start
				case sCmp <= 0:
					// Right partial overlap; truncate old start.
					//
					// New: --------          --------
					// Old:     --------  or  ------------
					//
					// Old:         ----              ----
					o.Key.Start = r.End
				default:
					panic(fmt.Sprintf("no overlap between %v and %v", o.Key.Range, r))
				}
			} else {
				// The existing interval has a timestamp greater than the new interval.
				// Compare interval ranges to determine how to modify new interval before
				// adding it to the timestamp cache.
				switch {
				case sCmp >= 0 && eCmp <= 0:
//.........這裏部分代碼省略.........

// fetch retrieves spans from the kv
func (f *kvFetcher) fetch() *roachpb.Error {
	// Retrieve all the spans.
	batchSize := int64(kvBatchSize)
	if f.firstBatchLimit != 0 && len(f.kvs) == 0 && f.firstBatchLimit < batchSize {
		batchSize = f.firstBatchLimit
	}

	b := &client.Batch{MaxScanResults: batchSize}

	var resumeKey roachpb.Key
	if len(f.kvs) > 0 {
		resumeKey = f.kvs[len(f.kvs)-1].Key
		// To resume forward scans we will set the (inclusive) scan start to the Next of the last
		// received key. To resume reverse scans we will set the (exclusive) scan end to the last
		// received key.
		if !f.reverse {
			resumeKey = resumeKey.ShallowNext()
		}
	}

	atEnd := true
	if !f.reverse {
		for i := 0; i < len(f.spans); i++ {
			start := f.spans[i].start
			if resumeKey != nil {
				if resumeKey.Compare(f.spans[i].end) >= 0 {
					// We are resuming from a key after this span.
					continue
				}
				if resumeKey.Compare(start) > 0 {
					// We are resuming from a key inside this span.
					// In this case we should technically reduce the max count for the span; but
					// since this count is only an optimization it's not incorrect to retrieve more
					// keys for the span.
					start = resumeKey
				}
			}
			atEnd = false
			b.Scan(start, f.spans[i].end, f.spans[i].count)
		}
	} else {
		for i := len(f.spans) - 1; i >= 0; i-- {
			end := f.spans[i].end
			if resumeKey != nil {
				if resumeKey.Compare(f.spans[i].start) <= 0 {
					// We are resuming from a key before this span.
					continue
				}
				if resumeKey.Compare(end) < 0 {
					// We are resuming from a key inside this span.
					// In this case we should technically reduce the max count for the span; but
					// since this count is only an optimization it's not incorrect to retrieve more
					// keys for the span.
					end = resumeKey
				}
			}
			atEnd = false
			b.ReverseScan(f.spans[i].start, end, f.spans[i].count)
		}
	}

	if atEnd {
		// The last scan happened to finish just at the end of the last span.
		f.kvs = nil
		f.fetchEnd = true
		return nil
	}

	if pErr := f.txn.Run(b); pErr != nil {
		return pErr
	}

	if f.kvs == nil {
		numResults := 0
		for _, result := range b.Results {
			numResults += len(result.Rows)
		}
		f.kvs = make([]client.KeyValue, 0, numResults)
	} else {
		f.kvs = f.kvs[:0]
	}

	for _, result := range b.Results {
		f.kvs = append(f.kvs, result.Rows...)
	}

	f.totalFetched += int64(len(f.kvs))
	f.kvIndex = 0

	if int64(len(f.kvs)) < batchSize {
		f.fetchEnd = true
	}

	// TODO(radu): We should fetch the next chunk in the background instead of waiting for the next
	// call to fetch(). We can use a pool of workers to issue the KV ops which will also limit the
	// total number of fetches that happen in parallel (and thus the amount of resources we use).
	return nil
}