rocksdb/db/db_iter.cc
jorlow@chromium.org e2da744e12 Upstream changes.
git-svn-id: https://leveldb.googlecode.com/svn/trunk@16 62dab493-f737-651d-591e-8d6aee1b9529
2011-03-28 20:43:44 +00:00

398 lines
11 KiB
C++

// 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 "db/db_iter.h"
#include "db/filename.h"
#include "db/dbformat.h"
#include "include/env.h"
#include "include/iterator.h"
#include "port/port.h"
#include "util/logging.h"
#include "util/mutexlock.h"
namespace leveldb {
#if 0
static void DumpInternalIter(Iterator* iter) {
for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
ParsedInternalKey k;
if (!ParseInternalKey(iter->key(), &k)) {
fprintf(stderr, "Corrupt '%s'\n", EscapeString(iter->key()).c_str());
} else {
fprintf(stderr, "@ '%s'\n", k.DebugString().c_str());
}
}
}
#endif
namespace {
// Memtables and sstables that make the DB representation contain
// (userkey,seq,type) => uservalue entries. DBIter
// combines multiple entries for the same userkey found in the DB
// representation into a single entry while accounting for sequence
// numbers, deletion markers, overwrites, etc.
class DBIter: public Iterator {
public:
// Which direction is the iterator currently moving?
// (1) When moving forward, the internal iterator is positioned at
// the exact entry that yields this->key(), this->value()
// (2) When moving backwards, the internal iterator is positioned
// just before all entries whose user key == this->key().
enum Direction {
kForward,
kReverse
};
DBIter(const std::string* dbname, Env* env,
const Comparator* cmp, Iterator* iter, SequenceNumber s)
: dbname_(dbname),
env_(env),
user_comparator_(cmp),
iter_(iter),
sequence_(s),
large_(NULL),
direction_(kForward),
valid_(false) {
}
virtual ~DBIter() {
delete iter_;
delete large_;
}
virtual bool Valid() const { return valid_; }
virtual Slice key() const {
assert(valid_);
return (direction_ == kForward) ? ExtractUserKey(iter_->key()) : saved_key_;
}
virtual Slice value() const {
assert(valid_);
Slice raw_value = (direction_ == kForward) ? iter_->value() : saved_value_;
if (large_ == NULL) {
return raw_value;
} else {
MutexLock l(&large_->mutex);
if (!large_->produced) {
ReadIndirectValue(raw_value);
}
return large_->value;
}
}
virtual Status status() const {
if (status_.ok()) {
if (large_ != NULL && !large_->status.ok()) return large_->status;
return iter_->status();
} else {
return status_;
}
}
virtual void Next();
virtual void Prev();
virtual void Seek(const Slice& target);
virtual void SeekToFirst();
virtual void SeekToLast();
private:
struct Large {
port::Mutex mutex;
std::string value;
bool produced;
Status status;
};
void FindNextUserEntry(bool skipping, std::string* skip);
void FindPrevUserEntry();
bool ParseKey(ParsedInternalKey* key);
void ReadIndirectValue(Slice ref) const;
inline void SaveKey(const Slice& k, std::string* dst) {
dst->assign(k.data(), k.size());
}
inline void ForgetLargeValue() {
if (large_ != NULL) {
delete large_;
large_ = NULL;
}
}
inline void ClearSavedValue() {
if (saved_value_.capacity() > 1048576) {
std::string empty;
swap(empty, saved_value_);
} else {
saved_value_.clear();
}
}
const std::string* const dbname_;
Env* const env_;
const Comparator* const user_comparator_;
Iterator* const iter_;
SequenceNumber const sequence_;
Status status_;
std::string saved_key_; // == current key when direction_==kReverse
std::string saved_value_; // == current raw value when direction_==kReverse
Large* large_; // Non-NULL if value is an indirect reference
Direction direction_;
bool valid_;
// No copying allowed
DBIter(const DBIter&);
void operator=(const DBIter&);
};
inline bool DBIter::ParseKey(ParsedInternalKey* ikey) {
if (!ParseInternalKey(iter_->key(), ikey)) {
status_ = Status::Corruption("corrupted internal key in DBIter");
return false;
} else {
return true;
}
}
void DBIter::Next() {
assert(valid_);
ForgetLargeValue();
if (direction_ == kReverse) { // Switch directions?
direction_ = kForward;
// iter_ is pointing just before the entries for this->key(),
// so advance into the range of entries for this->key() and then
// use the normal skipping code below.
if (!iter_->Valid()) {
iter_->SeekToFirst();
} else {
iter_->Next();
}
if (!iter_->Valid()) {
valid_ = false;
saved_key_.clear();
return;
}
}
// Temporarily use saved_key_ as storage for key to skip.
std::string* skip = &saved_key_;
SaveKey(ExtractUserKey(iter_->key()), skip);
FindNextUserEntry(true, skip);
}
void DBIter::FindNextUserEntry(bool skipping, std::string* skip) {
// Loop until we hit an acceptable entry to yield
assert(iter_->Valid());
assert(direction_ == kForward);
assert(large_ == NULL);
do {
ParsedInternalKey ikey;
if (ParseKey(&ikey) && ikey.sequence <= sequence_) {
switch (ikey.type) {
case kTypeDeletion:
// Arrange to skip all upcoming entries for this key since
// they are hidden by this deletion.
SaveKey(ikey.user_key, skip);
skipping = true;
break;
case kTypeValue:
case kTypeLargeValueRef:
if (skipping &&
user_comparator_->Compare(ikey.user_key, *skip) <= 0) {
// Entry hidden
} else {
valid_ = true;
saved_key_.clear();
if (ikey.type == kTypeLargeValueRef) {
large_ = new Large;
large_->produced = false;
}
return;
}
break;
}
}
iter_->Next();
} while (iter_->Valid());
saved_key_.clear();
valid_ = false;
}
void DBIter::Prev() {
assert(valid_);
ForgetLargeValue();
if (direction_ == kForward) { // Switch directions?
// iter_ is pointing at the current entry. Scan backwards until
// the key changes so we can use the normal reverse scanning code.
assert(iter_->Valid()); // Otherwise valid_ would have been false
SaveKey(ExtractUserKey(iter_->key()), &saved_key_);
while (true) {
iter_->Prev();
if (!iter_->Valid()) {
valid_ = false;
saved_key_.clear();
ClearSavedValue();
return;
}
if (user_comparator_->Compare(ExtractUserKey(iter_->key()),
saved_key_) < 0) {
break;
}
}
direction_ = kReverse;
}
FindPrevUserEntry();
}
void DBIter::FindPrevUserEntry() {
assert(direction_ == kReverse);
assert(large_ == NULL);
ValueType value_type = kTypeDeletion;
if (iter_->Valid()) {
SaveKey(ExtractUserKey(iter_->key()), &saved_key_);
do {
ParsedInternalKey ikey;
if (ParseKey(&ikey) && ikey.sequence <= sequence_) {
if ((value_type != kTypeDeletion) &&
user_comparator_->Compare(ikey.user_key, saved_key_) < 0) {
// We encountered a non-deleted value in entries for previous keys,
break;
}
value_type = ikey.type;
if (value_type == kTypeDeletion) {
ClearSavedValue();
} else {
Slice raw_value = iter_->value();
if (saved_value_.capacity() > raw_value.size() + 1048576) {
std::string empty;
swap(empty, saved_value_);
}
saved_value_.assign(raw_value.data(), raw_value.size());
}
}
iter_->Prev();
} while (iter_->Valid());
}
if (value_type == kTypeDeletion) {
// End
valid_ = false;
saved_key_.clear();
ClearSavedValue();
direction_ = kForward;
} else {
valid_ = true;
if (value_type == kTypeLargeValueRef) {
large_ = new Large;
large_->produced = false;
}
}
}
void DBIter::Seek(const Slice& target) {
direction_ = kForward;
ForgetLargeValue();
ClearSavedValue();
saved_key_.clear();
AppendInternalKey(
&saved_key_, ParsedInternalKey(target, sequence_, kValueTypeForSeek));
iter_->Seek(saved_key_);
if (iter_->Valid()) {
FindNextUserEntry(false, &saved_key_ /* temporary storage */);
} else {
valid_ = false;
}
}
void DBIter::SeekToFirst() {
direction_ = kForward;
ForgetLargeValue();
ClearSavedValue();
iter_->SeekToFirst();
if (iter_->Valid()) {
FindNextUserEntry(false, &saved_key_ /* temporary storage */);
} else {
valid_ = false;
}
}
void DBIter::SeekToLast() {
direction_ = kReverse;
ForgetLargeValue();
ClearSavedValue();
iter_->SeekToLast();
FindPrevUserEntry();
}
void DBIter::ReadIndirectValue(Slice ref) const {
assert(!large_->produced);
large_->produced = true;
LargeValueRef large_ref;
if (ref.size() != LargeValueRef::ByteSize()) {
large_->status = Status::Corruption("malformed large value reference");
return;
}
memcpy(large_ref.data, ref.data(), LargeValueRef::ByteSize());
std::string fname = LargeValueFileName(*dbname_, large_ref);
RandomAccessFile* file;
Status s = env_->NewRandomAccessFile(fname, &file);
uint64_t file_size = 0;
if (s.ok()) {
s = env_->GetFileSize(fname, &file_size);
}
if (s.ok()) {
uint64_t value_size = large_ref.ValueSize();
large_->value.resize(value_size);
Slice result;
s = file->Read(0, file_size, &result,
const_cast<char*>(large_->value.data()));
if (s.ok()) {
if (result.size() == file_size) {
switch (large_ref.compression_type()) {
case kNoCompression: {
if (result.data() != large_->value.data()) {
large_->value.assign(result.data(), result.size());
}
break;
}
case kSnappyCompression: {
std::string uncompressed;
if (port::Snappy_Uncompress(result.data(), result.size(),
&uncompressed) &&
uncompressed.size() == large_ref.ValueSize()) {
swap(uncompressed, large_->value);
} else {
s = Status::Corruption(
"Unable to read entire compressed large value file");
}
}
}
} else {
s = Status::Corruption("Unable to read entire large value file");
}
}
delete file; // Ignore errors on closing
}
if (!s.ok()) {
large_->value.clear();
large_->status = s;
}
}
} // anonymous namespace
Iterator* NewDBIterator(
const std::string* dbname,
Env* env,
const Comparator* user_key_comparator,
Iterator* internal_iter,
const SequenceNumber& sequence) {
return new DBIter(dbname, env, user_key_comparator, internal_iter, sequence);
}
}