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Diffstat (limited to 'src/leveldb/db/db_iter.cc')
| -rw-r--r-- | src/leveldb/db/db_iter.cc | 299 |
1 files changed, 299 insertions, 0 deletions
diff --git a/src/leveldb/db/db_iter.cc b/src/leveldb/db/db_iter.cc new file mode 100644 index 0000000000..87dca2ded4 --- /dev/null +++ b/src/leveldb/db/db_iter.cc @@ -0,0 +1,299 @@ +// 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 "leveldb/env.h" +#include "leveldb/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), + direction_(kForward), + valid_(false) { + } + virtual ~DBIter() { + delete iter_; + } + 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_); + return (direction_ == kForward) ? iter_->value() : saved_value_; + } + virtual Status status() const { + if (status_.ok()) { + 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: + void FindNextUserEntry(bool skipping, std::string* skip); + void FindPrevUserEntry(); + bool ParseKey(ParsedInternalKey* key); + + inline void SaveKey(const Slice& k, std::string* dst) { + dst->assign(k.data(), k.size()); + } + + 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 + 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_); + + 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); + 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: + if (skipping && + user_comparator_->Compare(ikey.user_key, *skip) <= 0) { + // Entry hidden + } else { + valid_ = true; + saved_key_.clear(); + return; + } + break; + } + } + iter_->Next(); + } while (iter_->Valid()); + saved_key_.clear(); + valid_ = false; +} + +void DBIter::Prev() { + assert(valid_); + + 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); + + ValueType value_type = kTypeDeletion; + if (iter_->Valid()) { + 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) { + saved_key_.clear(); + ClearSavedValue(); + } else { + Slice raw_value = iter_->value(); + if (saved_value_.capacity() > raw_value.size() + 1048576) { + std::string empty; + swap(empty, saved_value_); + } + SaveKey(ExtractUserKey(iter_->key()), &saved_key_); + 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; + } +} + +void DBIter::Seek(const Slice& target) { + direction_ = kForward; + 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; + ClearSavedValue(); + iter_->SeekToFirst(); + if (iter_->Valid()) { + FindNextUserEntry(false, &saved_key_ /* temporary storage */); + } else { + valid_ = false; + } +} + +void DBIter::SeekToLast() { + direction_ = kReverse; + ClearSavedValue(); + iter_->SeekToLast(); + FindPrevUserEntry(); +} + +} // 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); +} + +} // namespace leveldb |