Golang RKey.Next方法代码示例

// getCachedRangeDescriptorLocked is a helper function to retrieve the
// descriptor of the range which contains the given key, if present in the
// cache. It is assumed that the caller holds a read lock on rdc.rangeCache.
func (rdc *rangeDescriptorCache) getCachedRangeDescriptorLocked(
	key roachpb.RKey, inclusive bool,
) (rangeCacheKey, *roachpb.RangeDescriptor, error) {
	// The cache is indexed using the end-key of the range, but the
	// end-key is non-inclusive by default.
	var metaKey roachpb.RKey
	var err error
	if !inclusive {
		metaKey, err = meta(key.Next())
	} else {
		metaKey, err = meta(key)
	}
	if err != nil {
		return nil, nil, err
	}

	k, v, ok := rdc.rangeCache.cache.Ceil(rangeCacheKey(metaKey))
	if !ok {
		return nil, nil, nil
	}
	metaEndKey := k.(rangeCacheKey)
	rd := v.(*roachpb.RangeDescriptor)

	containsFn := (*roachpb.RangeDescriptor).ContainsKey
	if inclusive {
		containsFn = (*roachpb.RangeDescriptor).ContainsExclusiveEndKey
	}

	// Return nil if the key does not belong to the range.
	if !containsFn(rd, key) {
		return nil, nil, nil
	}
	return metaEndKey, rd, nil
}

// MetaScanBounds returns the range [start,end) within which the desired meta
// record can be found by means of an engine scan. The given key must be a
// valid RangeMetaKey as defined by validateRangeMetaKey.
// TODO(tschottdorf): a lot of casting going on inside.
func MetaScanBounds(key roachpb.RKey) (roachpb.Key, roachpb.Key, error) {
	if err := validateRangeMetaKey(key); err != nil {
		return nil, nil, err
	}

	if key.Equal(Meta2KeyMax) {
		return nil, nil, NewInvalidRangeMetaKeyError("Meta2KeyMax can't be used as the key of scan", key)
	}

	if key.Equal(roachpb.RKeyMin) {
		// Special case KeyMin: find the first entry in meta1.
		return Meta1Prefix, Meta1Prefix.PrefixEnd(), nil
	}
	if key.Equal(Meta1KeyMax) {
		// Special case Meta1KeyMax: this is the last key in Meta1, we don't want
		// to start at Next().
		return Meta1KeyMax, Meta1Prefix.PrefixEnd(), nil
	}
	// Otherwise find the first entry greater than the given key in the same meta prefix.
	return key.Next().AsRawKey(), key[:len(Meta1Prefix)].PrefixEnd().AsRawKey(), nil
}

// MetaReverseScanBounds returns the range [start,end) within which the desired
// meta record can be found by means of a reverse engine scan. The given key
// must be a valid RangeMetaKey as defined by validateRangeMetaKey.
func MetaReverseScanBounds(key roachpb.RKey) (roachpb.Key, roachpb.Key, error) {
	if err := validateRangeMetaKey(key); err != nil {
		return nil, nil, err
	}

	if key.Equal(roachpb.RKeyMin) || key.Equal(Meta1Prefix) {
		return nil, nil, NewInvalidRangeMetaKeyError("KeyMin and Meta1Prefix can't be used as the key of reverse scan", key)
	}
	if key.Equal(Meta2Prefix) {
		// Special case Meta2Prefix: this is the first key in Meta2, and the scan
		// interval covers all of Meta1.
		return Meta1Prefix, key.Next().AsRawKey(), nil
	}
	// Otherwise find the first entry greater than the given key and find the last entry
	// in the same prefix. For MVCCReverseScan the endKey is exclusive, if we want to find
	// the range descriptor the given key specified,we need to set the key.Next() as the
	// MVCCReverseScan`s endKey. For example:
	// If we have ranges [a,f) and [f,z), then we'll have corresponding meta records
	// at f and z. If you're looking for the meta record for key f, then you want the
	// second record (exclusive in MVCCReverseScan), hence key.Next() below.
	return key[:len(Meta1Prefix)].AsRawKey(), key.Next().AsRawKey(), nil
}