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LevelDB-course-Lab/table/table_test.cc

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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#include "leveldb/table.h"
#include <map>
#include <string>
#include "gtest/gtest.h"
#include "db/dbformat.h"
#include "db/memtable.h"
#include "db/write_batch_internal.h"
#include "leveldb/db.h"
#include "leveldb/env.h"
#include "leveldb/iterator.h"
#include "leveldb/options.h"
#include "leveldb/table_builder.h"
#include "table/block.h"
#include "table/block_builder.h"
#include "table/format.h"
#include "util/random.h"
#include "util/testutil.h"
namespace leveldb {
// Return reverse of "key".
// Used to test non-lexicographic comparators.
static std::string Reverse(const Slice& key) {
std::string str(key.ToString());
std::string rev("");
for (std::string::reverse_iterator rit = str.rbegin(); rit != str.rend();
++rit) {
rev.push_back(*rit);
}
return rev;
}
namespace {
class ReverseKeyComparator : public Comparator {
public:
const char* Name() const override {
return "leveldb.ReverseBytewiseComparator";
}
int Compare(const Slice& a, const Slice& b) const override {
return BytewiseComparator()->Compare(Reverse(a), Reverse(b));
}
void FindShortestSeparator(std::string* start,
const Slice& limit) const override {
std::string s = Reverse(*start);
std::string l = Reverse(limit);
BytewiseComparator()->FindShortestSeparator(&s, l);
*start = Reverse(s);
}
void FindShortSuccessor(std::string* key) const override {
std::string s = Reverse(*key);
BytewiseComparator()->FindShortSuccessor(&s);
*key = Reverse(s);
}
};
} // namespace
static ReverseKeyComparator reverse_key_comparator;
static void Increment(const Comparator* cmp, std::string* key) {
if (cmp == BytewiseComparator()) {
key->push_back('\0');
} else {
assert(cmp == &reverse_key_comparator);
std::string rev = Reverse(*key);
rev.push_back('\0');
*key = Reverse(rev);
}
}
// An STL comparator that uses a Comparator
namespace {
struct STLLessThan {
const Comparator* cmp;
STLLessThan() : cmp(BytewiseComparator()) {}
STLLessThan(const Comparator* c) : cmp(c) {}
bool operator()(const std::string& a, const std::string& b) const {
return cmp->Compare(Slice(a), Slice(b)) < 0;
}
};
} // namespace
class StringSink : public WritableFile {
public:
~StringSink() override = default;
const std::string& contents() const { return contents_; }
Status Close() override { return Status::OK(); }
Status Flush() override { return Status::OK(); }
Status Sync() override { return Status::OK(); }
Status Append(const Slice& data) override {
contents_.append(data.data(), data.size());
return Status::OK();
}
private:
std::string contents_;
};
class StringSource : public RandomAccessFile {
public:
StringSource(const Slice& contents)
: contents_(contents.data(), contents.size()) {}
~StringSource() override = default;
uint64_t Size() const { return contents_.size(); }
Status Read(uint64_t offset, size_t n, Slice* result,
char* scratch) const override {
if (offset >= contents_.size()) {
return Status::InvalidArgument("invalid Read offset");
}
if (offset + n > contents_.size()) {
n = contents_.size() - offset;
}
std::memcpy(scratch, &contents_[offset], n);
*result = Slice(scratch, n);
return Status::OK();
}
private:
std::string contents_;
};
typedef std::map<std::string, std::string, STLLessThan> KVMap;
// Helper class for tests to unify the interface between
// BlockBuilder/TableBuilder and Block/Table.
class Constructor {
public:
explicit Constructor(const Comparator* cmp) : data_(STLLessThan(cmp)) {}
virtual ~Constructor() = default;
void Add(const std::string& key, const Slice& value) {
data_[key] = value.ToString();
}
// Finish constructing the data structure with all the keys that have
// been added so far. Returns the keys in sorted order in "*keys"
// and stores the key/value pairs in "*kvmap"
void Finish(const Options& options, std::vector<std::string>* keys,
KVMap* kvmap) {
*kvmap = data_;
keys->clear();
for (const auto& kvp : data_) {
keys->push_back(kvp.first);
}
data_.clear();
Status s = FinishImpl(options, *kvmap);
ASSERT_TRUE(s.ok()) << s.ToString();
}
// Construct the data structure from the data in "data"
virtual Status FinishImpl(const Options& options, const KVMap& data) = 0;
virtual Iterator* NewIterator() const = 0;
const KVMap& data() const { return data_; }
virtual DB* db() const { return nullptr; } // Overridden in DBConstructor
private:
KVMap data_;
};
class BlockConstructor : public Constructor {
public:
explicit BlockConstructor(const Comparator* cmp)
: Constructor(cmp), comparator_(cmp), block_(nullptr) {}
~BlockConstructor() override { delete block_; }
Status FinishImpl(const Options& options, const KVMap& data) override {
delete block_;
block_ = nullptr;
BlockBuilder builder(&options);
for (const auto& kvp : data) {
builder.Add(kvp.first, kvp.second);
}
// Open the block
data_ = builder.Finish().ToString();
BlockContents contents;
contents.data = data_;
contents.cachable = false;
contents.heap_allocated = false;
block_ = new Block(contents);
return Status::OK();
}
Iterator* NewIterator() const override {
return block_->NewIterator(comparator_);
}
private:
const Comparator* const comparator_;
std::string data_;
Block* block_;
BlockConstructor();
};
class TableConstructor : public Constructor {
public:
TableConstructor(const Comparator* cmp)
: Constructor(cmp), source_(nullptr), table_(nullptr) {}
~TableConstructor() override { Reset(); }
Status FinishImpl(const Options& options, const KVMap& data) override {
Reset();
StringSink sink;
TableBuilder builder(options, &sink);
for (const auto& kvp : data) {
builder.Add(kvp.first, kvp.second);
EXPECT_LEVELDB_OK(builder.status());
}
Status s = builder.Finish();
EXPECT_LEVELDB_OK(s);
EXPECT_EQ(sink.contents().size(), builder.FileSize());
// Open the table
source_ = new StringSource(sink.contents());
Options table_options;
table_options.comparator = options.comparator;
return Table::Open(table_options, source_, sink.contents().size(), &table_);
}
Iterator* NewIterator() const override {
return table_->NewIterator(ReadOptions());
}
uint64_t ApproximateOffsetOf(const Slice& key) const {
return table_->ApproximateOffsetOf(key);
}
private:
void Reset() {
delete table_;
delete source_;
table_ = nullptr;
source_ = nullptr;
}
StringSource* source_;
Table* table_;
TableConstructor();
};
// A helper class that converts internal format keys into user keys
class KeyConvertingIterator : public Iterator {
public:
explicit KeyConvertingIterator(Iterator* iter) : iter_(iter) {}
KeyConvertingIterator(const KeyConvertingIterator&) = delete;
KeyConvertingIterator& operator=(const KeyConvertingIterator&) = delete;
~KeyConvertingIterator() override { delete iter_; }
bool Valid() const override { return iter_->Valid(); }
void Seek(const Slice& target) override {
ParsedInternalKey ikey(target, kMaxSequenceNumber, kTypeValue);
std::string encoded;
AppendInternalKey(&encoded, ikey);
iter_->Seek(encoded);
}
void SeekToFirst() override { iter_->SeekToFirst(); }
void SeekToLast() override { iter_->SeekToLast(); }
void Next() override { iter_->Next(); }
void Prev() override { iter_->Prev(); }
Slice key() const override {
assert(Valid());
ParsedInternalKey key;
if (!ParseInternalKey(iter_->key(), &key)) {
status_ = Status::Corruption("malformed internal key");
return Slice("corrupted key");
}
return key.user_key;
}
Slice value() const override { return iter_->value(); }
Status status() const override {
return status_.ok() ? iter_->status() : status_;
}
private:
mutable Status status_;
Iterator* iter_;
};
class MemTableConstructor : public Constructor {
public:
explicit MemTableConstructor(const Comparator* cmp)
: Constructor(cmp), internal_comparator_(cmp) {
memtable_ = new MemTable(internal_comparator_);
memtable_->Ref();
}
~MemTableConstructor() override { memtable_->Unref(); }
Status FinishImpl(const Options& options, const KVMap& data) override {
memtable_->Unref();
memtable_ = new MemTable(internal_comparator_);
memtable_->Ref();
int seq = 1;
for (const auto& kvp : data) {
memtable_->Add(seq, kTypeValue, kvp.first, kvp.second);
seq++;
}
return Status::OK();
}
Iterator* NewIterator() const override {
return new KeyConvertingIterator(memtable_->NewIterator());
}
private:
const InternalKeyComparator internal_comparator_;
MemTable* memtable_;
};
class DBConstructor : public Constructor {
public:
explicit DBConstructor(const Comparator* cmp)
: Constructor(cmp), comparator_(cmp) {
db_ = nullptr;
NewDB();
}
~DBConstructor() override { delete db_; }
Status FinishImpl(const Options& options, const KVMap& data) override {
delete db_;
db_ = nullptr;
NewDB();
for (const auto& kvp : data) {
WriteBatch batch;
batch.Put(kvp.first, kvp.second);
EXPECT_TRUE(db_->Write(WriteOptions(), &batch).ok());
}
return Status::OK();
}
Iterator* NewIterator() const override {
return db_->NewIterator(ReadOptions());
}
DB* db() const override { return db_; }
private:
void NewDB() {
std::string name = testing::TempDir() + "table_testdb";
Options options;
options.comparator = comparator_;
Status status = DestroyDB(name, options);
ASSERT_TRUE(status.ok()) << status.ToString();
options.create_if_missing = true;
options.error_if_exists = true;
options.write_buffer_size = 10000; // Something small to force merging
status = DB::Open(options, name, &db_);
ASSERT_TRUE(status.ok()) << status.ToString();
}
const Comparator* const comparator_;
DB* db_;
};
enum TestType { TABLE_TEST, BLOCK_TEST, MEMTABLE_TEST, DB_TEST };
struct TestArgs {
TestType type;
bool reverse_compare;
int restart_interval;
};
static const TestArgs kTestArgList[] = {
{TABLE_TEST, false, 16},
{TABLE_TEST, false, 1},
{TABLE_TEST, false, 1024},
{TABLE_TEST, true, 16},
{TABLE_TEST, true, 1},
{TABLE_TEST, true, 1024},
{BLOCK_TEST, false, 16},
{BLOCK_TEST, false, 1},
{BLOCK_TEST, false, 1024},
{BLOCK_TEST, true, 16},
{BLOCK_TEST, true, 1},
{BLOCK_TEST, true, 1024},
// Restart interval does not matter for memtables
{MEMTABLE_TEST, false, 16},
{MEMTABLE_TEST, true, 16},
// Do not bother with restart interval variations for DB
{DB_TEST, false, 16},
{DB_TEST, true, 16},
};
static const int kNumTestArgs = sizeof(kTestArgList) / sizeof(kTestArgList[0]);
class Harness : public testing::Test {
public:
Harness() : constructor_(nullptr) {}
void Init(const TestArgs& args) {
delete constructor_;
constructor_ = nullptr;
options_ = Options();
options_.block_restart_interval = args.restart_interval;
// Use shorter block size for tests to exercise block boundary
// conditions more.
options_.block_size = 256;
if (args.reverse_compare) {
options_.comparator = &reverse_key_comparator;
}
switch (args.type) {
case TABLE_TEST:
constructor_ = new TableConstructor(options_.comparator);
break;
case BLOCK_TEST:
constructor_ = new BlockConstructor(options_.comparator);
break;
case MEMTABLE_TEST:
constructor_ = new MemTableConstructor(options_.comparator);
break;
case DB_TEST:
constructor_ = new DBConstructor(options_.comparator);
break;
}
}
~Harness() { delete constructor_; }
void Add(const std::string& key, const std::string& value) {
constructor_->Add(key, value);
}
void Test(Random* rnd) {
std::vector<std::string> keys;
KVMap data;
constructor_->Finish(options_, &keys, &data);
TestForwardScan(keys, data);
TestBackwardScan(keys, data);
TestRandomAccess(rnd, keys, data);
}
void TestForwardScan(const std::vector<std::string>& keys,
const KVMap& data) {
Iterator* iter = constructor_->NewIterator();
ASSERT_TRUE(!iter->Valid());
iter->SeekToFirst();
for (KVMap::const_iterator model_iter = data.begin();
model_iter != data.end(); ++model_iter) {
ASSERT_EQ(ToString(data, model_iter), ToString(iter));
iter->Next();
}
ASSERT_TRUE(!iter->Valid());
delete iter;
}
void TestBackwardScan(const std::vector<std::string>& keys,
const KVMap& data) {
Iterator* iter = constructor_->NewIterator();
ASSERT_TRUE(!iter->Valid());
iter->SeekToLast();
for (KVMap::const_reverse_iterator model_iter = data.rbegin();
model_iter != data.rend(); ++model_iter) {
ASSERT_EQ(ToString(data, model_iter), ToString(iter));
iter->Prev();
}
ASSERT_TRUE(!iter->Valid());
delete iter;
}
void TestRandomAccess(Random* rnd, const std::vector<std::string>& keys,
const KVMap& data) {
static const bool kVerbose = false;
Iterator* iter = constructor_->NewIterator();
ASSERT_TRUE(!iter->Valid());
KVMap::const_iterator model_iter = data.begin();
if (kVerbose) std::fprintf(stderr, "---\n");
for (int i = 0; i < 200; i++) {
const int toss = rnd->Uniform(5);
switch (toss) {
case 0: {
if (iter->Valid()) {
if (kVerbose) std::fprintf(stderr, "Next\n");
iter->Next();
++model_iter;
ASSERT_EQ(ToString(data, model_iter), ToString(iter));
}
break;
}
case 1: {
if (kVerbose) std::fprintf(stderr, "SeekToFirst\n");
iter->SeekToFirst();
model_iter = data.begin();
ASSERT_EQ(ToString(data, model_iter), ToString(iter));
break;
}
case 2: {
std::string key = PickRandomKey(rnd, keys);
model_iter = data.lower_bound(key);
if (kVerbose)
std::fprintf(stderr, "Seek '%s'\n", EscapeString(key).c_str());
iter->Seek(Slice(key));
ASSERT_EQ(ToString(data, model_iter), ToString(iter));
break;
}
case 3: {
if (iter->Valid()) {
if (kVerbose) std::fprintf(stderr, "Prev\n");
iter->Prev();
if (model_iter == data.begin()) {
model_iter = data.end(); // Wrap around to invalid value
} else {
--model_iter;
}
ASSERT_EQ(ToString(data, model_iter), ToString(iter));
}
break;
}
case 4: {
if (kVerbose) std::fprintf(stderr, "SeekToLast\n");
iter->SeekToLast();
if (keys.empty()) {
model_iter = data.end();
} else {
std::string last = data.rbegin()->first;
model_iter = data.lower_bound(last);
}
ASSERT_EQ(ToString(data, model_iter), ToString(iter));
break;
}
}
}
delete iter;
}
std::string ToString(const KVMap& data, const KVMap::const_iterator& it) {
if (it == data.end()) {
return "END";
} else {
return "'" + it->first + "->" + it->second + "'";
}
}
std::string ToString(const KVMap& data,
const KVMap::const_reverse_iterator& it) {
if (it == data.rend()) {
return "END";
} else {
return "'" + it->first + "->" + it->second + "'";
}
}
std::string ToString(const Iterator* it) {
if (!it->Valid()) {
return "END";
} else {
return "'" + it->key().ToString() + "->" + it->value().ToString() + "'";
}
}
std::string PickRandomKey(Random* rnd, const std::vector<std::string>& keys) {
if (keys.empty()) {
return "foo";
} else {
const int index = rnd->Uniform(keys.size());
std::string result = keys[index];
switch (rnd->Uniform(3)) {
case 0:
// Return an existing key
break;
case 1: {
// Attempt to return something smaller than an existing key
if (!result.empty() && result[result.size() - 1] > '\0') {
result[result.size() - 1]--;
}
break;
}
case 2: {
// Return something larger than an existing key
Increment(options_.comparator, &result);
break;
}
}
return result;
}
}
// Returns nullptr if not running against a DB
DB* db() const { return constructor_->db(); }
private:
Options options_;
Constructor* constructor_;
};
// Test empty table/block.
TEST_F(Harness, Empty) {
for (int i = 0; i < kNumTestArgs; i++) {
Init(kTestArgList[i]);
Random rnd(test::RandomSeed() + 1);
Test(&rnd);
}
}
// Special test for a block with no restart entries. The C++ leveldb
// code never generates such blocks, but the Java version of leveldb
// seems to.
TEST_F(Harness, ZeroRestartPointsInBlock) {
char data[sizeof(uint32_t)];
memset(data, 0, sizeof(data));
BlockContents contents;
contents.data = Slice(data, sizeof(data));
contents.cachable = false;
contents.heap_allocated = false;
Block block(contents);
Iterator* iter = block.NewIterator(BytewiseComparator());
iter->SeekToFirst();
ASSERT_TRUE(!iter->Valid());
iter->SeekToLast();
ASSERT_TRUE(!iter->Valid());
iter->Seek("foo");
ASSERT_TRUE(!iter->Valid());
delete iter;
}
// Test the empty key
TEST_F(Harness, SimpleEmptyKey) {
for (int i = 0; i < kNumTestArgs; i++) {
Init(kTestArgList[i]);
Random rnd(test::RandomSeed() + 1);
Add("", "v");
Test(&rnd);
}
}
TEST_F(Harness, SimpleSingle) {
for (int i = 0; i < kNumTestArgs; i++) {
Init(kTestArgList[i]);
Random rnd(test::RandomSeed() + 2);
Add("abc", "v");
Test(&rnd);
}
}
TEST_F(Harness, SimpleMulti) {
for (int i = 0; i < kNumTestArgs; i++) {
Init(kTestArgList[i]);
Random rnd(test::RandomSeed() + 3);
Add("abc", "v");
Add("abcd", "v");
Add("ac", "v2");
Test(&rnd);
}
}
TEST_F(Harness, SimpleSpecialKey) {
for (int i = 0; i < kNumTestArgs; i++) {
Init(kTestArgList[i]);
Random rnd(test::RandomSeed() + 4);
Add("\xff\xff", "v3");
Test(&rnd);
}
}
TEST_F(Harness, Randomized) {
for (int i = 0; i < kNumTestArgs; i++) {
Init(kTestArgList[i]);
Random rnd(test::RandomSeed() + 5);
for (int num_entries = 0; num_entries < 2000;
num_entries += (num_entries < 50 ? 1 : 200)) {
if ((num_entries % 10) == 0) {
std::fprintf(stderr, "case %d of %d: num_entries = %d\n", (i + 1),
int(kNumTestArgs), num_entries);
}
for (int e = 0; e < num_entries; e++) {
std::string v;
Add(test::RandomKey(&rnd, rnd.Skewed(4)),
test::RandomString(&rnd, rnd.Skewed(5), &v).ToString());
}
Test(&rnd);
}
}
}
TEST_F(Harness, RandomizedLongDB) {
Random rnd(test::RandomSeed());
TestArgs args = {DB_TEST, false, 16};
Init(args);
int num_entries = 100000;
for (int e = 0; e < num_entries; e++) {
std::string v;
Add(test::RandomKey(&rnd, rnd.Skewed(4)),
test::RandomString(&rnd, rnd.Skewed(5), &v).ToString());
}
Test(&rnd);
// We must have created enough data to force merging
int files = 0;
for (int level = 0; level < config::kNumLevels; level++) {
std::string value;
char name[100];
std::snprintf(name, sizeof(name), "leveldb.num-files-at-level%d", level);
ASSERT_TRUE(db()->GetProperty(name, &value));
files += atoi(value.c_str());
}
ASSERT_GT(files, 0);
}
TEST(MemTableTest, Simple) {
InternalKeyComparator cmp(BytewiseComparator());
MemTable* memtable = new MemTable(cmp);
memtable->Ref();
WriteBatch batch;
WriteBatchInternal::SetSequence(&batch, 100);
batch.Put(std::string("k1"), std::string("v1"));
batch.Put(std::string("k2"), std::string("v2"));
batch.Put(std::string("k3"), std::string("v3"));
batch.Put(std::string("largekey"), std::string("vlarge"));
ASSERT_TRUE(WriteBatchInternal::InsertInto(&batch, memtable).ok());
Iterator* iter = memtable->NewIterator();
iter->SeekToFirst();
while (iter->Valid()) {
std::fprintf(stderr, "key: '%s' -> '%s'\n", iter->key().ToString().c_str(),
iter->value().ToString().c_str());
iter->Next();
}
delete iter;
memtable->Unref();
}
static bool Between(uint64_t val, uint64_t low, uint64_t high) {
bool result = (val >= low) && (val <= high);
if (!result) {
std::fprintf(stderr, "Value %llu is not in range [%llu, %llu]\n",
(unsigned long long)(val), (unsigned long long)(low),
(unsigned long long)(high));
}
return result;
}
TEST(TableTest, ApproximateOffsetOfPlain) {
TableConstructor c(BytewiseComparator());
c.Add("k01", "hello");
c.Add("k02", "hello2");
c.Add("k03", std::string(10000, 'x'));
c.Add("k04", std::string(200000, 'x'));
c.Add("k05", std::string(300000, 'x'));
c.Add("k06", "hello3");
c.Add("k07", std::string(100000, 'x'));
std::vector<std::string> keys;
KVMap kvmap;
Options options;
options.block_size = 1024;
options.compression = kNoCompression;
c.Finish(options, &keys, &kvmap);
ASSERT_TRUE(Between(c.ApproximateOffsetOf("abc"), 0, 0));
ASSERT_TRUE(Between(c.ApproximateOffsetOf("k01"), 0, 0));
ASSERT_TRUE(Between(c.ApproximateOffsetOf("k01a"), 0, 0));
ASSERT_TRUE(Between(c.ApproximateOffsetOf("k02"), 0, 0));
ASSERT_TRUE(Between(c.ApproximateOffsetOf("k03"), 0, 0));
ASSERT_TRUE(Between(c.ApproximateOffsetOf("k04"), 10000, 11000));
ASSERT_TRUE(Between(c.ApproximateOffsetOf("k04a"), 210000, 211000));
ASSERT_TRUE(Between(c.ApproximateOffsetOf("k05"), 210000, 211000));
ASSERT_TRUE(Between(c.ApproximateOffsetOf("k06"), 510000, 511000));
ASSERT_TRUE(Between(c.ApproximateOffsetOf("k07"), 510000, 511000));
ASSERT_TRUE(Between(c.ApproximateOffsetOf("xyz"), 610000, 612000));
}
static bool CompressionSupported(CompressionType type) {
std::string out;
Slice in = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
if (type == kSnappyCompression) {
return port::Snappy_Compress(in.data(), in.size(), &out);
} else if (type == kZstdCompression) {
return port::Zstd_Compress(/*level=*/1, in.data(), in.size(), &out);
}
return false;
}
class CompressionTableTest
: public ::testing::TestWithParam<std::tuple<CompressionType>> {};
INSTANTIATE_TEST_SUITE_P(CompressionTests, CompressionTableTest,
::testing::Values(kSnappyCompression,
kZstdCompression));
TEST_P(CompressionTableTest, ApproximateOffsetOfCompressed) {
CompressionType type = ::testing::get<0>(GetParam());
if (!CompressionSupported(type)) {
GTEST_SKIP() << "skipping compression test: " << type;
}
Random rnd(301);
TableConstructor c(BytewiseComparator());
std::string tmp;
c.Add("k01", "hello");
c.Add("k02", test::CompressibleString(&rnd, 0.25, 10000, &tmp));
c.Add("k03", "hello3");
c.Add("k04", test::CompressibleString(&rnd, 0.25, 10000, &tmp));
std::vector<std::string> keys;
KVMap kvmap;
Options options;
options.block_size = 1024;
options.compression = type;
c.Finish(options, &keys, &kvmap);
// Expected upper and lower bounds of space used by compressible strings.
static const int kSlop = 1000; // Compressor effectiveness varies.
const int expected = 2500; // 10000 * compression ratio (0.25)
const int min_z = expected - kSlop;
const int max_z = expected + kSlop;
ASSERT_TRUE(Between(c.ApproximateOffsetOf("abc"), 0, kSlop));
ASSERT_TRUE(Between(c.ApproximateOffsetOf("k01"), 0, kSlop));
ASSERT_TRUE(Between(c.ApproximateOffsetOf("k02"), 0, kSlop));
// Have now emitted a large compressible string, so adjust expected offset.
ASSERT_TRUE(Between(c.ApproximateOffsetOf("k03"), min_z, max_z));
ASSERT_TRUE(Between(c.ApproximateOffsetOf("k04"), min_z, max_z));
// Have now emitted two large compressible strings, so adjust expected offset.
ASSERT_TRUE(Between(c.ApproximateOffsetOf("xyz"), 2 * min_z, 2 * max_z));
}
} // namespace leveldb