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author | jorlow@chromium.org <jorlow@chromium.org@62dab493-f737-651d-591e-8d6aee1b9529> | 2011-03-18 22:37:00 +0000 |
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committer | jorlow@chromium.org <jorlow@chromium.org@62dab493-f737-651d-591e-8d6aee1b9529> | 2011-03-18 22:37:00 +0000 |
commit | f67e15e50f392625b4097caf22e8be1b0fe96013 (patch) | |
tree | 1cb1764c7627f9bac27ed0e0abf27010156e5007 /table/merger.cc | |
parent | 54f1fd7eef101db1dfb2bb66a59083c45a38aa4a (diff) | |
download | leveldb-f67e15e50f392625b4097caf22e8be1b0fe96013.tar.gz |
Initial checkin.
git-svn-id: https://leveldb.googlecode.com/svn/trunk@2 62dab493-f737-651d-591e-8d6aee1b9529
Diffstat (limited to 'table/merger.cc')
-rw-r--r-- | table/merger.cc | 143 |
1 files changed, 143 insertions, 0 deletions
diff --git a/table/merger.cc b/table/merger.cc new file mode 100644 index 0000000..74c1aaa --- /dev/null +++ b/table/merger.cc @@ -0,0 +1,143 @@ +// 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 "table/merger.h" + +#include "include/comparator.h" +#include "include/iterator.h" +#include "table/iterator_wrapper.h" + +namespace leveldb { + +namespace { +class MergingIterator : public Iterator { + public: + MergingIterator(const Comparator* comparator, Iterator** children, int n) + : comparator_(comparator), + children_(new IteratorWrapper[n]), + n_(n), + current_(NULL) { + for (int i = 0; i < n; i++) { + children_[i].Set(children[i]); + } + } + + virtual ~MergingIterator() { + delete[] children_; + } + + virtual bool Valid() const { + return (current_ != NULL); + } + + virtual void SeekToFirst() { + for (int i = 0; i < n_; i++) { + children_[i].SeekToFirst(); + } + FindSmallest(); + } + + virtual void SeekToLast() { + for (int i = 0; i < n_; i++) { + children_[i].SeekToLast(); + } + FindLargest(); + } + + virtual void Seek(const Slice& target) { + for (int i = 0; i < n_; i++) { + children_[i].Seek(target); + } + FindSmallest(); + } + + virtual void Next() { + assert(Valid()); + current_->Next(); + FindSmallest(); + } + + virtual void Prev() { + assert(Valid()); + current_->Prev(); + FindLargest(); + } + + virtual Slice key() const { + assert(Valid()); + return current_->key(); + } + + virtual Slice value() const { + assert(Valid()); + return current_->value(); + } + + virtual Status status() const { + Status status; + for (int i = 0; i < n_; i++) { + status = children_[i].status(); + if (!status.ok()) { + break; + } + } + return status; + } + + private: + void FindSmallest(); + void FindLargest(); + + // We might want to use a heap in case there are lots of children. + // For now we use a simple array since we expect a very small number + // of children in leveldb. + const Comparator* comparator_; + IteratorWrapper* children_; + int n_; + IteratorWrapper* current_; +}; + +void MergingIterator::FindSmallest() { + IteratorWrapper* smallest = NULL; + for (int i = 0; i < n_; i++) { + IteratorWrapper* child = &children_[i]; + if (child->Valid()) { + if (smallest == NULL) { + smallest = child; + } else if (comparator_->Compare(child->key(), smallest->key()) < 0) { + smallest = child; + } + } + } + current_ = smallest; +} + +void MergingIterator::FindLargest() { + IteratorWrapper* largest = NULL; + for (int i = n_-1; i >= 0; i--) { + IteratorWrapper* child = &children_[i]; + if (child->Valid()) { + if (largest == NULL) { + largest = child; + } else if (comparator_->Compare(child->key(), largest->key()) > 0) { + largest = child; + } + } + } + current_ = largest; +} +} + +Iterator* NewMergingIterator(const Comparator* cmp, Iterator** list, int n) { + assert(n >= 0); + if (n == 0) { + return NewEmptyIterator(); + } else if (n == 1) { + return list[0]; + } else { + return new MergingIterator(cmp, list, n); + } +} + +} |