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merging_iter_test.go
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merging_iter_test.go
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// Copyright 2018 The LevelDB-Go and Pebble Authors. All rights reserved. Use
// of this source code is governed by a BSD-style license that can be found in
// the LICENSE file.
package pebble
import (
"bytes"
"context"
"fmt"
"strconv"
"strings"
"testing"
"time"
"github.com/cockroachdb/datadriven"
"github.com/cockroachdb/pebble/bloom"
"github.com/cockroachdb/pebble/internal/base"
"github.com/cockroachdb/pebble/internal/itertest"
"github.com/cockroachdb/pebble/internal/keyspan"
"github.com/cockroachdb/pebble/internal/manifest"
"github.com/cockroachdb/pebble/internal/rangedel"
"github.com/cockroachdb/pebble/internal/testkeys"
"github.com/cockroachdb/pebble/objstorage/objstorageprovider"
"github.com/cockroachdb/pebble/sstable"
"github.com/cockroachdb/pebble/vfs"
"github.com/stretchr/testify/require"
"golang.org/x/exp/rand"
)
func TestMergingIter(t *testing.T) {
var stats base.InternalIteratorStats
newFunc := func(iters ...internalIterator) internalIterator {
return newMergingIter(nil /* logger */, &stats, DefaultComparer.Compare,
func(a []byte) int { return len(a) }, iters...)
}
testIterator(t, newFunc, func(r *rand.Rand) [][]string {
// Shuffle testKeyValuePairs into one or more splits. Each individual
// split is in increasing order, but different splits may overlap in
// range. Some of the splits may be empty.
splits := make([][]string, 1+r.Intn(2+len(testKeyValuePairs)))
for _, kv := range testKeyValuePairs {
j := r.Intn(len(splits))
splits[j] = append(splits[j], kv)
}
return splits
})
}
func TestMergingIterSeek(t *testing.T) {
var def string
datadriven.RunTest(t, "testdata/merging_iter_seek", func(t *testing.T, d *datadriven.TestData) string {
switch d.Cmd {
case "define":
def = d.Input
return ""
case "iter":
var iters []internalIterator
for _, line := range strings.Split(def, "\n") {
f := &fakeIter{}
for _, key := range strings.Fields(line) {
j := strings.Index(key, ":")
f.kvs = append(f.kvs, base.MakeInternalKV(base.ParseInternalKey(key[:j]), []byte(key[j+1:])))
}
iters = append(iters, f)
}
var stats base.InternalIteratorStats
iter := newMergingIter(nil /* logger */, &stats, DefaultComparer.Compare,
func(a []byte) int { return len(a) }, iters...)
defer iter.Close()
return itertest.RunInternalIterCmd(t, d, iter)
default:
return fmt.Sprintf("unknown command: %s", d.Cmd)
}
})
}
func TestMergingIterNextPrev(t *testing.T) {
// The data is the same in each of these cases, but divided up amongst the
// iterators differently. This data must match the definition in
// testdata/internal_iter_next.
iterCases := [][]string{
{
"a.SET.2:2 a.SET.1:1 b.SET.2:2 b.SET.1:1 c.SET.2:2 c.SET.1:1",
},
{
"a.SET.2:2 b.SET.2:2 c.SET.2:2",
"a.SET.1:1 b.SET.1:1 c.SET.1:1",
},
{
"a.SET.2:2 b.SET.2:2",
"a.SET.1:1 b.SET.1:1",
"c.SET.2:2 c.SET.1:1",
},
{
"a.SET.2:2",
"a.SET.1:1",
"b.SET.2:2",
"b.SET.1:1",
"c.SET.2:2",
"c.SET.1:1",
},
}
for _, c := range iterCases {
t.Run("", func(t *testing.T) {
datadriven.RunTest(t, "testdata/internal_iter_next", func(t *testing.T, d *datadriven.TestData) string {
switch d.Cmd {
case "define":
// Ignore. We've defined the iterator data above.
return ""
case "iter":
iters := make([]internalIterator, len(c))
for i := range c {
f := &fakeIter{}
iters[i] = f
for _, key := range strings.Fields(c[i]) {
j := strings.Index(key, ":")
f.kvs = append(f.kvs, base.MakeInternalKV(base.ParseInternalKey(key[:j]), []byte(key[j+1:])))
}
}
var stats base.InternalIteratorStats
iter := newMergingIter(nil /* logger */, &stats, DefaultComparer.Compare,
func(a []byte) int { return len(a) }, iters...)
defer iter.Close()
return itertest.RunInternalIterCmd(t, d, iter)
default:
return fmt.Sprintf("unknown command: %s", d.Cmd)
}
})
})
}
}
func TestMergingIterCornerCases(t *testing.T) {
memFS := vfs.NewMem()
cmp := DefaultComparer.Compare
fmtKey := DefaultComparer.FormatKey
opts := (*Options)(nil).EnsureDefaults()
var v *version
var buf bytes.Buffer
// Indexed by FileNum.
var readers []*sstable.Reader
defer func() {
for _, r := range readers {
r.Close()
}
}()
parser := itertest.NewParser()
var (
pointProbes map[base.FileNum][]itertest.Probe
rangeDelProbes map[base.FileNum][]keyspanProbe
fileNum base.FileNum
)
newIters :=
func(_ context.Context, file *manifest.FileMetadata, opts *IterOptions, iio internalIterOpts, kinds iterKinds,
) (iterSet, error) {
r := readers[file.FileNum]
rangeDelIter, err := r.NewRawRangeDelIter(sstable.NoTransforms)
if err != nil {
return iterSet{}, err
}
iter, err := r.NewIterWithBlockPropertyFilters(
sstable.NoTransforms,
opts.GetLowerBound(), opts.GetUpperBound(), nil, true /* useFilterBlock */, iio.stats,
sstable.CategoryAndQoS{}, nil, sstable.TrivialReaderProvider{Reader: r})
if err != nil {
return iterSet{}, err
}
return iterSet{
point: itertest.Attach(iter, itertest.ProbeState{Log: &buf}, pointProbes[file.FileNum]...),
rangeDeletion: attachKeyspanProbes(rangeDelIter, keyspanProbeContext{log: &buf}, rangeDelProbes[file.FileNum]...),
}, nil
}
datadriven.RunTest(t, "testdata/merging_iter", func(t *testing.T, d *datadriven.TestData) string {
switch d.Cmd {
case "define":
lines := strings.Split(d.Input, "\n")
var files [numLevels][]*fileMetadata
var level int
for i := 0; i < len(lines); i++ {
line := lines[i]
line = strings.TrimSpace(line)
if line == "L" || line == "L0" {
// start next level
level++
continue
}
keys := strings.Fields(line)
smallestKey := base.ParseInternalKey(keys[0])
largestKey := base.ParseInternalKey(keys[1])
m := (&fileMetadata{
FileNum: fileNum,
}).ExtendPointKeyBounds(cmp, smallestKey, largestKey)
m.InitPhysicalBacking()
files[level] = append(files[level], m)
i++
line = lines[i]
line = strings.TrimSpace(line)
name := fmt.Sprint(fileNum)
fileNum++
f, err := memFS.Create(name, vfs.WriteCategoryUnspecified)
if err != nil {
return err.Error()
}
w := sstable.NewWriter(objstorageprovider.NewFileWritable(f), sstable.WriterOptions{})
var tombstones []keyspan.Span
frag := keyspan.Fragmenter{
Cmp: cmp,
Format: fmtKey,
Emit: func(fragmented keyspan.Span) {
tombstones = append(tombstones, fragmented)
},
}
keyvalues := strings.Fields(line)
for _, kv := range keyvalues {
j := strings.Index(kv, ":")
ikey := base.ParseInternalKey(kv[:j])
value := []byte(kv[j+1:])
switch ikey.Kind() {
case InternalKeyKindRangeDelete:
frag.Add(keyspan.Span{Start: ikey.UserKey, End: value, Keys: []keyspan.Key{{Trailer: ikey.Trailer}}})
default:
if err := w.Add(ikey, value); err != nil {
return err.Error()
}
}
}
frag.Finish()
for _, v := range tombstones {
if err := rangedel.Encode(&v, w.Add); err != nil {
return err.Error()
}
}
if err := w.Close(); err != nil {
return err.Error()
}
f, err = memFS.Open(name)
if err != nil {
return err.Error()
}
readable, err := sstable.NewSimpleReadable(f)
if err != nil {
return err.Error()
}
r, err := sstable.NewReader(readable, sstable.ReaderOptions{})
if err != nil {
return err.Error()
}
readers = append(readers, r)
}
v = newVersion(opts, files)
return v.String()
case "iter":
buf.Reset()
pointProbes = make(map[base.FileNum][]itertest.Probe, len(v.Levels))
rangeDelProbes = make(map[base.FileNum][]keyspanProbe, len(v.Levels))
for _, cmdArg := range d.CmdArgs {
switch key := cmdArg.Key; key {
case "probe-points":
i, err := strconv.Atoi(cmdArg.Vals[0][1:])
if err != nil {
require.NoError(t, err)
}
pointProbes[base.FileNum(i)] = itertest.MustParseProbes(parser, cmdArg.Vals[1:]...)
case "probe-rangedels":
i, err := strconv.Atoi(cmdArg.Vals[0][1:])
if err != nil {
require.NoError(t, err)
}
rangeDelProbes[base.FileNum(i)] = parseKeyspanProbes(cmdArg.Vals[1:]...)
default:
// Might be a command understood by the RunInternalIterCmd
// command, so don't error.
}
}
levelIters := make([]mergingIterLevel, 0, len(v.Levels))
var stats base.InternalIteratorStats
for i, l := range v.Levels {
slice := l.Slice()
if slice.Empty() {
continue
}
li := &levelIter{}
li.init(context.Background(), IterOptions{}, testkeys.Comparer,
newIters, slice.Iter(), manifest.Level(i), internalIterOpts{stats: &stats})
i := len(levelIters)
levelIters = append(levelIters, mergingIterLevel{iter: li})
li.initRangeDel(&levelIters[i].rangeDelIter)
li.initBoundaryContext(&levelIters[i].levelIterBoundaryContext)
}
miter := &mergingIter{}
miter.init(nil /* opts */, &stats, cmp, func(a []byte) int { return len(a) }, levelIters...)
defer miter.Close()
miter.forceEnableSeekOpt = true
// Exercise SetContext for fun
// (https://github.com/cockroachdb/pebble/pull/3037 caused a SIGSEGV due
// to a nil pointer dereference).
miter.SetContext(context.Background())
itertest.RunInternalIterCmdWriter(t, &buf, d, miter,
itertest.Verbose, itertest.WithStats(&stats))
return buf.String()
default:
return fmt.Sprintf("unknown command: %s", d.Cmd)
}
})
}
func buildMergingIterTables(
b *testing.B, blockSize, restartInterval, count int,
) ([]*sstable.Reader, [][]byte, func()) {
mem := vfs.NewMem()
files := make([]vfs.File, count)
for i := range files {
f, err := mem.Create(fmt.Sprintf("bench%d", i), vfs.WriteCategoryUnspecified)
if err != nil {
b.Fatal(err)
}
files[i] = f
}
writers := make([]*sstable.Writer, len(files))
for i := range files {
writers[i] = sstable.NewWriter(objstorageprovider.NewFileWritable(files[i]), sstable.WriterOptions{
BlockRestartInterval: restartInterval,
BlockSize: blockSize,
Compression: NoCompression,
})
}
estimatedSize := func() uint64 {
var sum uint64
for _, w := range writers {
sum += w.EstimatedSize()
}
return sum
}
var keys [][]byte
var ikey InternalKey
targetSize := uint64(count * (2 << 20))
for i := 0; estimatedSize() < targetSize; i++ {
key := []byte(fmt.Sprintf("%08d", i))
keys = append(keys, key)
ikey.UserKey = key
j := rand.Intn(len(writers))
w := writers[j]
w.Add(ikey, nil)
}
for _, w := range writers {
if err := w.Close(); err != nil {
b.Fatal(err)
}
}
opts := sstable.ReaderOptions{Cache: NewCache(128 << 20)}
defer opts.Cache.Unref()
readers := make([]*sstable.Reader, len(files))
for i := range files {
f, err := mem.Open(fmt.Sprintf("bench%d", i))
if err != nil {
b.Fatal(err)
}
readable, err := sstable.NewSimpleReadable(f)
if err != nil {
b.Fatal(err)
}
readers[i], err = sstable.NewReader(readable, opts)
if err != nil {
b.Fatal(err)
}
}
return readers, keys, func() {
for _, r := range readers {
require.NoError(b, r.Close())
}
}
}
func BenchmarkMergingIterSeekGE(b *testing.B) {
const blockSize = 32 << 10
for _, restartInterval := range []int{16} {
b.Run(fmt.Sprintf("restart=%d", restartInterval),
func(b *testing.B) {
for _, count := range []int{1, 2, 3, 4, 5} {
b.Run(fmt.Sprintf("count=%d", count),
func(b *testing.B) {
readers, keys, cleanup := buildMergingIterTables(b, blockSize, restartInterval, count)
defer cleanup()
iters := make([]internalIterator, len(readers))
for i := range readers {
var err error
iters[i], err = readers[i].NewIter(sstable.NoTransforms, nil /* lower */, nil /* upper */)
require.NoError(b, err)
}
var stats base.InternalIteratorStats
m := newMergingIter(nil /* logger */, &stats, DefaultComparer.Compare,
func(a []byte) int { return len(a) }, iters...)
rng := rand.New(rand.NewSource(uint64(time.Now().UnixNano())))
b.ResetTimer()
for i := 0; i < b.N; i++ {
m.SeekGE(keys[rng.Intn(len(keys))], base.SeekGEFlagsNone)
}
m.Close()
})
}
})
}
}
func BenchmarkMergingIterNext(b *testing.B) {
const blockSize = 32 << 10
for _, restartInterval := range []int{16} {
b.Run(fmt.Sprintf("restart=%d", restartInterval),
func(b *testing.B) {
for _, count := range []int{1, 2, 3, 4, 5} {
b.Run(fmt.Sprintf("count=%d", count),
func(b *testing.B) {
readers, _, cleanup := buildMergingIterTables(b, blockSize, restartInterval, count)
defer cleanup()
iters := make([]internalIterator, len(readers))
for i := range readers {
var err error
iters[i], err = readers[i].NewIter(sstable.NoTransforms, nil /* lower */, nil /* upper */)
require.NoError(b, err)
}
var stats base.InternalIteratorStats
m := newMergingIter(nil /* logger */, &stats, DefaultComparer.Compare,
func(a []byte) int { return len(a) }, iters...)
b.ResetTimer()
for i := 0; i < b.N; i++ {
kv := m.Next()
if kv == nil {
kv = m.First()
}
_ = kv
}
m.Close()
})
}
})
}
}
func BenchmarkMergingIterPrev(b *testing.B) {
const blockSize = 32 << 10
for _, restartInterval := range []int{16} {
b.Run(fmt.Sprintf("restart=%d", restartInterval),
func(b *testing.B) {
for _, count := range []int{1, 2, 3, 4, 5} {
b.Run(fmt.Sprintf("count=%d", count),
func(b *testing.B) {
readers, _, cleanup := buildMergingIterTables(b, blockSize, restartInterval, count)
defer cleanup()
iters := make([]internalIterator, len(readers))
for i := range readers {
var err error
iters[i], err = readers[i].NewIter(sstable.NoTransforms, nil /* lower */, nil /* upper */)
require.NoError(b, err)
}
var stats base.InternalIteratorStats
m := newMergingIter(nil /* logger */, &stats, DefaultComparer.Compare,
func(a []byte) int { return len(a) }, iters...)
b.ResetTimer()
for i := 0; i < b.N; i++ {
kv := m.Prev()
if kv == nil {
kv = m.Last()
}
_ = kv
}
m.Close()
})
}
})
}
}
// Builds levels for BenchmarkMergingIterSeqSeekGEWithBounds. The lowest level,
// index 0 here, contains most of the data. Each level has 2 files, to allow for
// stepping into the second file if needed. The lowest level has all the keys in
// the file 0, and a single "lastIKey" in file 1. File 0 in all other levels have
// only the first and last key of file 0 of the aforementioned level -- this
// simulates sparseness of data, but not necessarily of file width, in higher
// levels. File 1 in other levels is similar to File 1 in the aforementioned level
// since it is only for stepping into. If writeRangeTombstoneToLowestLevel is
// true, a range tombstone is written to the first lowest level file that
// deletes all the keys in it, and no other levels should be written.
func buildLevelsForMergingIterSeqSeek(
b *testing.B,
blockSize, restartInterval, levelCount int,
keyOffset int,
writeRangeTombstoneToLowestLevel bool,
writeBloomFilters bool,
forceTwoLevelIndex bool,
) (readers [][]*sstable.Reader, levelSlices []manifest.LevelSlice, keys [][]byte) {
mem := vfs.NewMem()
if writeRangeTombstoneToLowestLevel && levelCount != 1 {
panic("expect to write only 1 level")
}
files := make([][]vfs.File, levelCount)
for i := range files {
for j := 0; j < 2; j++ {
f, err := mem.Create(fmt.Sprintf("bench%d_%d", i, j), vfs.WriteCategoryUnspecified)
if err != nil {
b.Fatal(err)
}
files[i] = append(files[i], f)
}
}
const targetL6FirstFileSize = 2 << 20
writers := make([][]*sstable.Writer, levelCount)
// A policy unlikely to have false positives.
filterPolicy := bloom.FilterPolicy(100)
for i := range files {
for j := range files[i] {
writerOptions := sstable.WriterOptions{
BlockRestartInterval: restartInterval,
BlockSize: blockSize,
Compression: NoCompression,
}
if writeBloomFilters {
writerOptions.FilterPolicy = filterPolicy
writerOptions.FilterType = base.TableFilter
}
if forceTwoLevelIndex {
if i == 0 && j == 0 {
// Ignoring compression, approximate number of blocks
numDataBlocks := targetL6FirstFileSize / blockSize
if numDataBlocks < 4 {
b.Fatalf("cannot produce two level index")
}
// Produce ~2 lower-level index blocks.
writerOptions.IndexBlockSize = (numDataBlocks / 2) * 8
} else if j == 0 {
// Only 2 keys in these files, so to produce two level indexes we
// set the block sizes to 1.
writerOptions.BlockSize = 1
writerOptions.IndexBlockSize = 1
}
}
writers[i] = append(writers[i], sstable.NewWriter(objstorageprovider.NewFileWritable(files[i][j]), writerOptions))
}
}
i := keyOffset
w := writers[0][0]
for ; w.EstimatedSize() < targetL6FirstFileSize; i++ {
key := []byte(fmt.Sprintf("%08d", i))
keys = append(keys, key)
ikey := base.MakeInternalKey(key, 0, InternalKeyKindSet)
w.Add(ikey, nil)
}
if writeRangeTombstoneToLowestLevel {
tombstoneKey := base.MakeInternalKey(keys[0], 1, InternalKeyKindRangeDelete)
w.Add(tombstoneKey, []byte(fmt.Sprintf("%08d", i)))
}
for j := 1; j < len(files); j++ {
for _, k := range []int{0, len(keys) - 1} {
ikey := base.MakeInternalKey(keys[k], uint64(j), InternalKeyKindSet)
writers[j][0].Add(ikey, nil)
}
}
lastKey := []byte(fmt.Sprintf("%08d", i))
keys = append(keys, lastKey)
for j := 0; j < len(files); j++ {
lastIKey := base.MakeInternalKey(lastKey, uint64(j), InternalKeyKindSet)
writers[j][1].Add(lastIKey, nil)
}
for _, levelWriters := range writers {
for j, w := range levelWriters {
if err := w.Close(); err != nil {
b.Fatal(err)
}
meta, err := w.Metadata()
require.NoError(b, err)
if forceTwoLevelIndex && j == 0 && meta.Properties.IndexType != 2 {
b.Fatalf("did not produce two level index")
}
}
}
opts := sstable.ReaderOptions{Cache: NewCache(128 << 20), Comparer: DefaultComparer}
if writeBloomFilters {
opts.Filters = make(map[string]FilterPolicy)
opts.Filters[filterPolicy.Name()] = filterPolicy
}
defer opts.Cache.Unref()
readers = make([][]*sstable.Reader, levelCount)
for i := range files {
for j := range files[i] {
f, err := mem.Open(fmt.Sprintf("bench%d_%d", i, j))
if err != nil {
b.Fatal(err)
}
readable, err := sstable.NewSimpleReadable(f)
if err != nil {
b.Fatal(err)
}
r, err := sstable.NewReader(readable, opts)
if err != nil {
b.Fatal(err)
}
readers[i] = append(readers[i], r)
}
}
levelSlices = make([]manifest.LevelSlice, levelCount)
for i := range readers {
meta := make([]*fileMetadata, len(readers[i]))
for j := range readers[i] {
iter, err := readers[i][j].NewIter(sstable.NoTransforms, nil /* lower */, nil /* upper */)
require.NoError(b, err)
smallest := iter.First()
meta[j] = &fileMetadata{}
// The same FileNum is being reused across different levels, which
// is harmless for the benchmark since each level has its own iterator
// creation func.
meta[j].FileNum = FileNum(j)
largest := iter.Last()
meta[j].ExtendPointKeyBounds(opts.Comparer.Compare, smallest.K.Clone(), largest.K.Clone())
meta[j].InitPhysicalBacking()
}
levelSlices[i] = manifest.NewLevelSliceSpecificOrder(meta)
}
return readers, levelSlices, keys
}
func buildMergingIter(readers [][]*sstable.Reader, levelSlices []manifest.LevelSlice) *mergingIter {
mils := make([]mergingIterLevel, len(levelSlices))
for i := len(readers) - 1; i >= 0; i-- {
levelIndex := i
level := len(readers) - 1 - i
newIters := func(
_ context.Context, file *manifest.FileMetadata, opts *IterOptions, _ internalIterOpts, _ iterKinds,
) (iterSet, error) {
iter, err := readers[levelIndex][file.FileNum].NewIter(
sstable.NoTransforms, opts.LowerBound, opts.UpperBound)
if err != nil {
return iterSet{}, err
}
rdIter, err := readers[levelIndex][file.FileNum].NewRawRangeDelIter(sstable.NoTransforms)
if err != nil {
iter.Close()
return iterSet{}, err
}
return iterSet{point: iter, rangeDeletion: rdIter}, err
}
l := newLevelIter(
context.Background(), IterOptions{}, testkeys.Comparer, newIters, levelSlices[i].Iter(),
manifest.Level(level), internalIterOpts{})
l.initRangeDel(&mils[level].rangeDelIter)
l.initBoundaryContext(&mils[level].levelIterBoundaryContext)
mils[level].iter = l
}
var stats base.InternalIteratorStats
m := &mergingIter{}
m.init(nil /* logger */, &stats, testkeys.Comparer.Compare,
func(a []byte) int { return len(a) }, mils...)
return m
}
// A benchmark that simulates the behavior of a mergingIter where
// monotonically increasing narrow bounds are repeatedly set and used to Seek
// and then iterate over the keys within the bounds. This resembles MVCC
// scanning by CockroachDB when doing a lookup/index join with a large number
// of left rows, that are batched and reuse the same iterator, and which can
// have good locality of access. This results in the successive bounds being
// in the same file.
func BenchmarkMergingIterSeqSeekGEWithBounds(b *testing.B) {
const blockSize = 32 << 10
restartInterval := 16
for _, levelCount := range []int{5} {
b.Run(fmt.Sprintf("levelCount=%d", levelCount),
func(b *testing.B) {
readers, levelSlices, keys := buildLevelsForMergingIterSeqSeek(
b, blockSize, restartInterval, levelCount, 0 /* keyOffset */, false, false, false)
m := buildMergingIter(readers, levelSlices)
keyCount := len(keys)
b.ResetTimer()
for i := 0; i < b.N; i++ {
pos := i % (keyCount - 1)
m.SetBounds(keys[pos], keys[pos+1])
// SeekGE will return keys[pos].
k := m.SeekGE(keys[pos], base.SeekGEFlagsNone)
for k != nil {
k = m.Next()
}
}
m.Close()
for i := range readers {
for j := range readers[i] {
readers[i][j].Close()
}
}
})
}
}
func BenchmarkMergingIterSeqSeekPrefixGE(b *testing.B) {
const blockSize = 32 << 10
const restartInterval = 16
const levelCount = 5
readers, levelSlices, keys := buildLevelsForMergingIterSeqSeek(
b, blockSize, restartInterval, levelCount, 0 /* keyOffset */, false, false, false)
for _, skip := range []int{1, 2, 4, 8, 16} {
for _, useNext := range []bool{false, true} {
b.Run(fmt.Sprintf("skip=%d/use-next=%t", skip, useNext),
func(b *testing.B) {
m := buildMergingIter(readers, levelSlices)
keyCount := len(keys)
pos := 0
m.SeekPrefixGE(keys[pos], keys[pos], base.SeekGEFlagsNone)
b.ResetTimer()
for i := 0; i < b.N; i++ {
pos += skip
var flags base.SeekGEFlags
if useNext {
flags = flags.EnableTrySeekUsingNext()
}
if pos >= keyCount {
pos = 0
flags = flags.DisableTrySeekUsingNext()
}
// SeekPrefixGE will return keys[pos].
m.SeekPrefixGE(keys[pos], keys[pos], flags)
}
b.StopTimer()
m.Close()
})
}
}
for i := range readers {
for j := range readers[i] {
readers[i][j].Close()
}
}
}