influxdb/tsdb/index/tsi1/index.go

package tsi1

import (
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"runtime"
	"strconv"
	"sync"
	"sync/atomic"

	"github.com/cespare/xxhash"
	"github.com/influxdata/influxdb/models"
	"github.com/influxdata/influxdb/pkg/estimator"
	"github.com/influxdata/influxdb/pkg/estimator/hll"
	"github.com/influxdata/influxdb/pkg/slices"
	"github.com/influxdata/influxdb/query"
	"github.com/influxdata/influxdb/tsdb"
	"github.com/influxdata/influxql"
	"go.uber.org/zap"
)

// IndexName is the name of the index.
const IndexName = "tsi1"

func init() {
	// FIXME(edd): Remove this.
	if os.Getenv("TSI_PARTITIONS") != "" {
		i, err := strconv.Atoi(os.Getenv("TSI_PARTITIONS"))
		if err != nil {
			panic(err)
		}
		DefaultPartitionN = uint64(i)
	}

	tsdb.RegisterIndex(IndexName, func(_ uint64, _, path string, sfile *tsdb.SeriesFile, _ tsdb.EngineOptions) tsdb.Index {
		idx := NewIndex(sfile, WithPath(path))
		return idx
	})
}

// DefaultPartitionN determines how many shards the index will be partitioned into.
//
// NOTE: Currently, this must not be change once a database is created. Further,
// it must also be a power of 2.
//
var DefaultPartitionN uint64 = 16

// An IndexOption is a functional option for changing the configuration of
// an Index.
type IndexOption func(i *Index)

// WithPath sets the root path of the Index
var WithPath = func(path string) IndexOption {
	return func(i *Index) {
		i.path = path
	}
}

// DisableCompactions disables compactions on the Index.
var DisableCompactions = func() IndexOption {
	return func(i *Index) {
		i.disableCompactions = true
	}
}

// WithLogger sets the logger for the Index.
var WithLogger = func(l zap.Logger) IndexOption {
	return func(i *Index) {
		i.logger = l.With(zap.String("index", "tsi"))
	}
}

// Index represents a collection of layered index files and WAL.
type Index struct {
	mu         sync.RWMutex
	partitions []*Partition
	opened     bool

	// The following can be set when initialising an Index.
	path               string      // Root directory of the index partitions.
	disableCompactions bool        // Initially disables compactions on the index.
	logger             *zap.Logger // Index's logger.

	sfile *tsdb.SeriesFile // series lookup file

	// Index's version.
	version int

	// Name of database.
	database string

	// Number of partitions used by the index.
	PartitionN uint64
}

// NewIndex returns a new instance of Index.
func NewIndex(sfile *tsdb.SeriesFile, options ...IndexOption) *Index {
	idx := &Index{
		logger:     zap.NewNop(),
		version:    Version,
		sfile:      sfile,
		PartitionN: DefaultPartitionN,
	}

	for _, option := range options {
		option(idx)
	}

	return idx
}

// Database returns the name of the database the index was initialized with.
func (i *Index) Database() string {
	return i.database
}

// WithLogger sets the logger on the index after it's been created.
//
// It's not safe to call WithLogger after the index has been opened, or before
// it has been closed.
func (i *Index) WithLogger(l *zap.Logger) {
	i.mu.Lock()
	defer i.mu.Unlock()

	for i, p := range i.partitions {
		p.logger = l.With(zap.String("index", "tsi"), zap.String("partition", fmt.Sprint(i+1)))
	}
	i.logger = l.With(zap.String("index", "tsi"))
}

// Type returns the type of Index this is.
func (i *Index) Type() string { return IndexName }

// SeriesFile returns the series file attached to the index.
func (i *Index) SeriesFile() *tsdb.SeriesFile { return i.sfile }

// Open opens the index.
func (i *Index) Open() error {
	i.mu.Lock()
	defer i.mu.Unlock()

	if i.opened {
		return errors.New("index already open")
	}

	// Ensure root exists.
	if err := os.MkdirAll(i.path, 0777); err != nil {
		return err
	}

	// Inititalise index partitions.
	i.partitions = make([]*Partition, i.PartitionN)
	for j := 0; j < len(i.partitions); j++ {
		p := NewPartition(i.sfile, filepath.Join(i.path, fmt.Sprint(j)))
		p.Database = i.database
		p.compactionsDisabled = i.disableCompactions
		p.logger = i.logger.With(zap.String("partition", fmt.Sprint(j+1)))
		i.partitions[j] = p
	}

	// Open all the Partitions in parallel.
	partitionN := len(i.partitions)
	n := i.availableThreads()

	// Store results.
	errC := make(chan error, partitionN)

	// Run fn on each partition using a fixed number of goroutines.
	var pidx uint32 // Index of maximum Partition being worked on.
	for k := 0; k < n; k++ {
		go func(k int) {
			for {
				idx := int(atomic.AddUint32(&pidx, 1) - 1) // Get next partition to work on.
				if idx >= partitionN {
					return // No more work.
				}
				errC <- i.partitions[idx].Open()
			}
		}(k)
	}

	// Check for error
	for i := 0; i < partitionN; i++ {
		if err := <-errC; err != nil {
			return err
		}
	}

	// Mark opened.
	i.opened = true
	i.logger.Info(fmt.Sprintf("index opened with %d partitions", partitionN))
	return nil
}

// Wait blocks until all outstanding compactions have completed.
func (i *Index) Wait() {
	for _, p := range i.partitions {
		p.Wait()
	}
}

// Close closes the index.
func (i *Index) Close() error {
	// Lock index and close partitions.
	i.mu.Lock()
	defer i.mu.Unlock()

	for _, p := range i.partitions {
		if err := p.Close(); err != nil {
			return err
		}
	}

	return nil
}

// Path returns the path the index was opened with.
func (i *Index) Path() string { return i.path }

// PartitionAt returns the partition by index.
func (i *Index) PartitionAt(index int) *Partition {
	return i.partitions[index]
}

// partition returns the appropriate Partition for a provided series key.
func (i *Index) partition(key []byte) *Partition {
	return i.partitions[int(xxhash.Sum64(key)&(i.PartitionN-1))]
}

// partitionIdx returns the index of the partition that key belongs in.
func (i *Index) partitionIdx(key []byte) int {
	return int(xxhash.Sum64(key) & (i.PartitionN - 1))
}

// availableThreads returns the minimum of GOMAXPROCS and the number of
// partitions in the Index.
func (i *Index) availableThreads() int {
	n := runtime.GOMAXPROCS(0)
	if len(i.partitions) < n {
		return len(i.partitions)
	}
	return n
}

// SetFieldSet sets a shared field set from the engine.
func (i *Index) SetFieldSet(fs *tsdb.MeasurementFieldSet) {
	for _, p := range i.partitions {
		p.SetFieldSet(fs)
	}
}

// FieldSet returns the assigned fieldset.
func (i *Index) FieldSet() *tsdb.MeasurementFieldSet {
	if len(i.partitions) == 0 {
		return nil
	}
	return i.partitions[0].FieldSet()
}

// ForEachMeasurementName iterates over all measurement names in the index,
// applying fn. Note, the provided function may be called concurrently, and it
// must be safe to do so.
//
// It returns the first error encountered, if any.
func (i *Index) ForEachMeasurementName(fn func(name []byte) error) error {
	n := i.availableThreads()

	// Store results.
	errC := make(chan error, i.PartitionN)

	// Run fn on each partition using a fixed number of goroutines.
	var pidx uint32 // Index of maximum Partition being worked on.
	for k := 0; k < n; k++ {
		go func() {
			for {
				idx := int(atomic.AddUint32(&pidx, 1) - 1) // Get next partition to work on.
				if idx >= len(i.partitions) {
					return // No more work.
				}
				errC <- i.partitions[idx].ForEachMeasurementName(fn)
			}
		}()
	}

	// Check for error
	for i := 0; i < cap(errC); i++ {
		if err := <-errC; err != nil {
			return err
		}
	}
	return nil
}

// MeasurementExists returns true if a measurement exists.
func (i *Index) MeasurementExists(name []byte) (bool, error) {
	n := i.availableThreads()

	// Store errors
	var found uint32 // Use this to signal we found the measurement.
	errC := make(chan error, i.PartitionN)

	// Check each partition for the measurement concurrently.
	var pidx uint32 // Index of maximum Partition being worked on.
	for k := 0; k < n; k++ {
		go func() {
			for {
				idx := int(atomic.AddUint32(&pidx, 1) - 1) // Get next partition to check
				if idx >= len(i.partitions) {
					return // No more work.
				}

				// Check if the measurement has been found. If it has don't
				// need to check this partition and can just move on.
				if atomic.LoadUint32(&found) == 1 {
					errC <- nil
					continue
				}

				b, err := i.partitions[idx].MeasurementExists(name)
				errC <- err
				if b {
					atomic.StoreUint32(&found, 1)
				}
			}
		}()
	}

	// Check for error
	for i := 0; i < cap(errC); i++ {
		if err := <-errC; err != nil {
			return false, err
		}
	}

	// Check if we found the measurement.
	return atomic.LoadUint32(&found) == 1, nil
}

// fetchByteValues is a helper for gathering values from each partition in the index,
// based on some criteria.
//
// fn is a function that works on partition idx and calls into some method on
// the partition that returns some ordered values.
func (i *Index) fetchByteValues(fn func(idx int) ([][]byte, error)) ([][]byte, error) {
	n := i.availableThreads()

	// Store results.
	names := make([][][]byte, i.PartitionN)
	errC := make(chan error, i.PartitionN)

	var pidx uint32 // Index of maximum Partition being worked on.
	for k := 0; k < n; k++ {
		go func() {
			for {
				idx := int(atomic.AddUint32(&pidx, 1) - 1) // Get next partition to work on.
				if idx >= len(i.partitions) {
					return // No more work.
				}

				pnames, err := fn(idx)

				// This is safe since there are no readers on names until all
				// the writers are done.
				names[idx] = pnames
				errC <- err
			}
		}()
	}

	// Check for error
	for i := 0; i < cap(errC); i++ {
		if err := <-errC; err != nil {
			return nil, err
		}
	}

	// It's now safe to read from names.
	return slices.MergeSortedBytes(names[:]...), nil
}

// MeasurementIterator returns an iterator over all measurements.
func (i *Index) MeasurementIterator() (tsdb.MeasurementIterator, error) {
	itrs := make([]tsdb.MeasurementIterator, 0, len(i.partitions))
	for _, p := range i.partitions {
		itr, err := p.MeasurementIterator()
		if err != nil {
			tsdb.MeasurementIterators(itrs).Close()
			return nil, err
		}
		itrs = append(itrs, itr)
	}
	return tsdb.MergeMeasurementIterators(itrs...), nil
}

// MeasurementSeriesIDIterator returns an iterator over all series in a measurement.
func (i *Index) MeasurementSeriesIDIterator(name []byte) (tsdb.SeriesIDIterator, error) {
	itrs := make([]tsdb.SeriesIDIterator, 0, len(i.partitions))
	for _, p := range i.partitions {
		itr, err := p.MeasurementSeriesIDIterator(name)
		if err != nil {
			tsdb.SeriesIDIterators(itrs).Close()
			return nil, err
		}
		itrs = append(itrs, itr)
	}
	return tsdb.MergeSeriesIDIterators(itrs...), nil
}

// MeasurementNamesByExpr returns measurement names for the provided expression.
func (i *Index) MeasurementNamesByExpr(expr influxql.Expr) ([][]byte, error) {
	return i.fetchByteValues(func(idx int) ([][]byte, error) {
		return i.partitions[idx].MeasurementNamesByExpr(expr)
	})
}

// MeasurementNamesByRegex returns measurement names for the provided regex.
func (i *Index) MeasurementNamesByRegex(re *regexp.Regexp) ([][]byte, error) {
	return i.fetchByteValues(func(idx int) ([][]byte, error) {
		return i.partitions[idx].MeasurementNamesByRegex(re)
	})
}

/*
// MeasurementSeriesKeysByExpr returns a list of series keys matching expr.
func (i *Index) MeasurementSeriesKeysByExpr(name []byte, expr influxql.Expr) ([][]byte, error) {
	return i.fetchByteValues(func(idx int) ([][]byte, error) {
		return i.partitions[idx].MeasurementSeriesKeysByExpr(name, expr)
	})
}
*/

// DropMeasurement deletes a measurement from the index. It returns the first
// error encountered, if any.
func (i *Index) DropMeasurement(name []byte) error {
	n := i.availableThreads()

	// Store results.
	errC := make(chan error, i.PartitionN)

	var pidx uint32 // Index of maximum Partition being worked on.
	for k := 0; k < n; k++ {
		go func() {
			for {
				idx := int(atomic.AddUint32(&pidx, 1) - 1) // Get next partition to work on.
				if idx >= len(i.partitions) {
					return // No more work.
				}
				errC <- i.partitions[idx].DropMeasurement(name)
			}
		}()
	}

	// Check for error
	for i := 0; i < cap(errC); i++ {
		if err := <-errC; err != nil {
			return err
		}
	}
	return nil
}

// CreateSeriesListIfNotExists creates a list of series if they doesn't exist in bulk.
func (i *Index) CreateSeriesListIfNotExists(_ [][]byte, names [][]byte, tagsSlice []models.Tags) error {
	// All slices must be of equal length.
	if len(names) != len(tagsSlice) {
		return errors.New("names/tags length mismatch in index")
	}

	// We need to move different series into collections for each partition
	// to process.
	pNames := make([][][]byte, i.PartitionN)
	pTags := make([][]models.Tags, i.PartitionN)

	// Determine partition for series using each series key.
	buf := make([]byte, 2048)
	for k, _ := range names {
		buf = tsdb.AppendSeriesKey(buf[:0], names[k], tagsSlice[k])

		pidx := i.partitionIdx(buf)
		pNames[pidx] = append(pNames[pidx], names[k])
		pTags[pidx] = append(pTags[pidx], tagsSlice[k])
	}

	// Process each subset of series on each partition.
	n := i.availableThreads()

	// Store errors.
	errC := make(chan error, i.PartitionN)

	var pidx uint32 // Index of maximum Partition being worked on.
	for k := 0; k < n; k++ {
		go func() {
			for {
				idx := int(atomic.AddUint32(&pidx, 1) - 1) // Get next partition to work on.
				if idx >= len(i.partitions) {
					return // No more work.
				}
				errC <- i.partitions[idx].createSeriesListIfNotExists(pNames[idx], pTags[idx])
			}
		}()
	}

	// Check for error
	for i := 0; i < cap(errC); i++ {
		if err := <-errC; err != nil {
			return err
		}
	}
	return nil
}

// CreateSeriesIfNotExists creates a series if it doesn't exist or is deleted.
func (i *Index) CreateSeriesIfNotExists(key, name []byte, tags models.Tags) error {
	return i.partition(key).createSeriesListIfNotExists([][]byte{name}, []models.Tags{tags})
}

// InitializeSeries is a no-op. This only applies to the in-memory index.
func (i *Index) InitializeSeries(key, name []byte, tags models.Tags) error {
	return nil
}

// DropSeries drops the provided series from the index.
func (i *Index) DropSeries(key []byte, ts int64) error {
	return i.partition(key).DropSeries(key, ts)
}

// MeasurementsSketches returns the two sketches for the index by merging all
// instances of the type sketch types in all the index files.
func (i *Index) MeasurementsSketches() (estimator.Sketch, estimator.Sketch, error) {
	s, ts := hll.NewDefaultPlus(), hll.NewDefaultPlus()
	for _, p := range i.partitions {
		// Get partition's measurement sketches and merge.
		ps, pts, err := p.MeasurementsSketches()
		if err != nil {
			return nil, nil, err
		}

		if err := s.Merge(ps); err != nil {
			return nil, nil, err
		} else if err := ts.Merge(pts); err != nil {
			return nil, nil, err
		}
	}

	return s, ts, nil
}

// SeriesN returns the number of unique non-tombstoned series in the index.
// Since indexes are not shared across shards, the count returned by SeriesN
// cannot be combined with other shard's results. If you need to count series
// across indexes then use SeriesSketches and merge the results from other
// indexes.
func (i *Index) SeriesN() int64 {
	return int64(i.sfile.SeriesCount())
}

// HasTagKey returns true if tag key exists. It returns the first error
// encountered if any.
func (i *Index) HasTagKey(name, key []byte) (bool, error) {
	n := i.availableThreads()

	// Store errors
	var found uint32 // Use this to signal we found the tag key.
	errC := make(chan error, i.PartitionN)

	// Check each partition for the tag key concurrently.
	var pidx uint32 // Index of maximum Partition being worked on.
	for k := 0; k < n; k++ {
		go func() {
			for {
				idx := int(atomic.AddUint32(&pidx, 1) - 1) // Get next partition to check
				if idx >= len(i.partitions) {
					return // No more work.
				}

				// Check if the tag key has already been found. If it has, we
				// don't need to check this partition and can just move on.
				if atomic.LoadUint32(&found) == 1 {
					errC <- nil
					continue
				}

				b, err := i.partitions[idx].HasTagKey(name, key)
				errC <- err
				if b {
					atomic.StoreUint32(&found, 1)
				}
			}
		}()
	}

	// Check for error
	for i := 0; i < cap(errC); i++ {
		if err := <-errC; err != nil {
			return false, err
		}
	}

	// Check if we found the tag key.
	return atomic.LoadUint32(&found) == 1, nil
}

// TagValueIterator returns an iterator for all values across a single key.
func (i *Index) TagValueIterator(auth query.Authorizer, name, key []byte) (tsdb.TagValueIterator, error) {
	a := make([]tsdb.TagValueIterator, 0, len(i.partitions))
	for _, p := range i.partitions {
		itr := p.TagValueIterator(name, key)
		if itr != nil {
			a = append(a, itr)
		}
	}
	return tsdb.MergeTagValueIterators(a...), nil
}

// TagKeySeriesIDIterator returns a series iterator for all values across a single key.
func (i *Index) TagKeySeriesIDIterator(name, key []byte) (tsdb.SeriesIDIterator, error) {
	a := make([]tsdb.SeriesIDIterator, 0, len(i.partitions))
	for _, p := range i.partitions {
		itr := p.TagKeySeriesIDIterator(name, key)
		if itr != nil {
			a = append(a, itr)
		}
	}
	return tsdb.MergeSeriesIDIterators(a...), nil
}

// TagValueSeriesIDIterator returns a series iterator for a single tag value.
func (i *Index) TagValueSeriesIDIterator(name, key, value []byte) (tsdb.SeriesIDIterator, error) {
	a := make([]tsdb.SeriesIDIterator, 0, len(i.partitions))
	for _, p := range i.partitions {
		itr := p.TagValueSeriesIDIterator(name, key, value)
		if itr != nil {
			a = append(a, itr)
		}
	}
	return tsdb.MergeSeriesIDIterators(a...), nil
}

// MeasurementTagKeysByExpr extracts the tag keys wanted by the expression.
func (i *Index) MeasurementTagKeysByExpr(name []byte, expr influxql.Expr) (map[string]struct{}, error) {
	n := i.availableThreads()

	// Store results.
	keys := make([]map[string]struct{}, i.PartitionN)
	errC := make(chan error, i.PartitionN)

	var pidx uint32 // Index of maximum Partition being worked on.
	var err error
	for k := 0; k < n; k++ {
		go func() {
			for {
				idx := int(atomic.AddUint32(&pidx, 1) - 1) // Get next partition to work on.
				if idx >= len(i.partitions) {
					return // No more work.
				}

				// This is safe since there are no readers on keys until all
				// the writers are done.
				keys[idx], err = i.partitions[idx].MeasurementTagKeysByExpr(name, expr)
				errC <- err
			}
		}()
	}

	// Check for error
	for i := 0; i < cap(errC); i++ {
		if err := <-errC; err != nil {
			return nil, err
		}
	}

	// Merge into single map.
	result := keys[0]
	for k := 1; k < len(i.partitions); k++ {
		for k := range keys[k] {
			result[k] = struct{}{}
		}
	}
	return result, nil
}

/*
// MeasurementTagKeyValuesByExpr returns a set of tag values filtered by an expression.
//
// See tsm1.Engine.MeasurementTagKeyValuesByExpr for a fuller description of this
// method.
func (i *Index) MeasurementTagKeyValuesByExpr(auth query.Authorizer, name []byte, keys []string, expr influxql.Expr, keysSorted bool) ([][]string, error) {
	if len(keys) == 0 {
		return nil, nil
	}

	// If we haven't been provided sorted keys, then we need to sort them.
	if !keysSorted {
		sort.Sort(sort.StringSlice(keys))
	}

	resultSet := make([]map[string]struct{}, len(keys))
	for i := 0; i < len(resultSet); i++ {
		resultSet[i] = make(map[string]struct{})
	}

	// No expression means that the values shouldn't be filtered, so we can
	// fetch them all.
	for _, p := range i.partitions {
		if err := func() error {
			fs := p.RetainFileSet()
			defer fs.Release()

			if expr == nil {
				for ki, key := range keys {
					itr := fs.TagValueIterator(name, []byte(key))
					if itr == nil {
						continue
					}
					if auth != nil {
						for val := itr.Next(); val != nil; val = itr.Next() {
							si := fs.TagValueSeriesIDIterator(name, []byte(key), val.Value())
							for {
								se, err := si.Next()
								if err != nil {
									return err
								} else if se.SeriesID == 0 {
									break
								}

								name, tags := tsdb.ParseSeriesKey(i.sfile.SeriesKey(se.SeriesID))
								if auth.AuthorizeSeriesRead(i.database, name, tags) {
									resultSet[ki][string(val.Value())] = struct{}{}
									break
								}
							}
						}
					} else {
						for val := itr.Next(); val != nil; val = itr.Next() {
							resultSet[ki][string(val.Value())] = struct{}{}
						}
					}
				}
				return nil
			}

			// This is the case where we have filtered series by some WHERE condition.
			// We only care about the tag values for the keys given the
			// filtered set of series ids.
			if err := fs.tagValuesByKeyAndExpr(auth, name, keys, expr, p.FieldSet(), resultSet); err != nil {
				return err
			}
			return nil
		}(); err != nil {
			return nil, err
		}
	}

	// Convert result sets into []string
	results := make([][]string, len(keys))
	for i, s := range resultSet {
		values := make([]string, 0, len(s))
		for v := range s {
			values = append(values, v)
		}
		sort.Sort(sort.StringSlice(values))
		results[i] = values
	}
	return results, nil
}
*/

// ForEachMeasurementTagKey iterates over all tag keys in a measurement and applies
// the provided function.
func (i *Index) ForEachMeasurementTagKey(name []byte, fn func(key []byte) error) error {
	for j := 0; j < len(i.partitions); j++ {
		if err := i.partitions[j].ForEachMeasurementTagKey(name, fn); err != nil {
			return err
		}
	}
	return nil
}

// TagKeyCardinality always returns zero.
// It is not possible to determine cardinality of tags across index files, and
// thus it cannot be done across partitions.
func (i *Index) TagKeyCardinality(name, key []byte) int {
	return 0
}

// SnapshotTo creates hard links to the file set into path.
func (i *Index) SnapshotTo(path string) error {
	newRoot := filepath.Join(path, "index")
	if err := os.Mkdir(newRoot, 0777); err != nil {
		return err
	}

	// Store results.
	errC := make(chan error, len(i.partitions))
	for _, p := range i.partitions {
		go func(p *Partition) {
			errC <- p.SnapshotTo(path)
		}(p)
	}

	// Check for error
	for i := 0; i < cap(errC); i++ {
		if err := <-errC; err != nil {
			return err
		}
	}
	return nil
}

// RetainFileSet returns the set of all files across all partitions.
// This is only needed when all files need to be retained for an operation.
func (i *Index) RetainFileSet() *FileSet {
	i.mu.RLock()
	defer i.mu.RUnlock()

	fs, _ := NewFileSet(i.database, nil, i.sfile, nil)
	for _, p := range i.partitions {
		pfs := p.RetainFileSet()
		fs.files = append(fs.files, pfs.files...)
	}
	return fs
}

func (i *Index) SetFieldName(measurement []byte, name string) {}
func (i *Index) RemoveShard(shardID uint64)                   {}
func (i *Index) AssignShard(k string, shardID uint64)         {}

func (i *Index) UnassignShard(k string, shardID uint64, ts int64) error {
	// This can be called directly once inmem is gone.
	return i.DropSeries([]byte(k), ts)
}

/*
// SeriesIDIterator returns a series iterator over all matching series.
func (i *Index) SeriesIDIterator(opt query.IteratorOptions) (tsdb.SeriesIDIterator, error) {
	itrs := make([]tsdb.SeriesIDIterator, 0, len(i.partitions))
	for k, p := range i.partitions {
		itrs = append(itrs, p.seriesIDIterator(opt))
	}
	return tsdb.MergeSeriesIDIterators(itrs...), nil
}
*/

func (i *Index) Rebuild() {}