btree.h

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/***************************************************************************
 *  include/stxxl/bits/containers/btree/btree.h
 *
 *  Part of the STXXL. See http://stxxl.sourceforge.net
 *
 *  Copyright (C) 2006, 2008 Roman Dementiev <[email protected]>
 *
 *  Distributed under the Boost Software License, Version 1.0.
 *  (See accompanying file LICENSE_1_0.txt or copy at
 *  http://www.boost.org/LICENSE_1_0.txt)
 **************************************************************************/

#ifndef STXXL_CONTAINERS_BTREE_BTREE_HEADER
#define STXXL_CONTAINERS_BTREE_BTREE_HEADER

#include <limits>
#include <stxxl/bits/namespace.h>
#include <stxxl/bits/containers/btree/iterator.h>
#include <stxxl/bits/containers/btree/iterator_map.h>
#include <stxxl/bits/containers/btree/leaf.h>
#include <stxxl/bits/containers/btree/node_cache.h>
#include <stxxl/bits/containers/btree/root_node.h>
#include <stxxl/bits/containers/btree/node.h>
#include <stxxl/vector>


STXXL_BEGIN_NAMESPACE

namespace btree {

template <class KeyType,
          class DataType,
          class CompareType,
          unsigned RawNodeSize,
          unsigned RawLeafSize,
          class PDAllocStrategy
          >
class btree : private noncopyable
{
public:
    typedef KeyType key_type;
    typedef DataType data_type;
    typedef CompareType key_compare;

    typedef btree<KeyType, DataType, CompareType, RawNodeSize, RawLeafSize, PDAllocStrategy> SelfType;

    typedef PDAllocStrategy alloc_strategy_type;

    typedef stxxl::uint64 size_type;
    typedef stxxl::int64 difference_type;
    typedef std::pair<const key_type, data_type> value_type;
    typedef value_type& reference;
    typedef const value_type& const_reference;
    typedef value_type* pointer;
    typedef value_type const* const_pointer;


    // leaf type declarations
    typedef normal_leaf<key_type, data_type, key_compare, RawLeafSize, SelfType> leaf_type;
    friend class normal_leaf<key_type, data_type, key_compare, RawLeafSize, SelfType>;
    typedef typename leaf_type::block_type leaf_block_type;
    typedef typename leaf_type::bid_type leaf_bid_type;
    typedef node_cache<leaf_type, SelfType> leaf_cache_type;
    friend class node_cache<leaf_type, SelfType>;
    // iterator types
    typedef btree_iterator<SelfType> iterator;
    typedef btree_const_iterator<SelfType> const_iterator;
    friend class btree_iterator_base<SelfType>;
    // iterator map type
    typedef iterator_map<SelfType> iterator_map_type;
    // node type declarations
    typedef normal_node<key_type, key_compare, RawNodeSize, SelfType> node_type;
    typedef typename node_type::block_type node_block_type;
    friend class normal_node<key_type, key_compare, RawNodeSize, SelfType>;
    typedef typename node_type::bid_type node_bid_type;
    typedef node_cache<node_type, SelfType> node_cache_type;
    friend class node_cache<node_type, SelfType>;

    typedef typename leaf_type::value_compare value_compare;

    enum {
        min_node_size = node_type::min_size,
        max_node_size = node_type::max_size,
        min_leaf_size = leaf_type::min_size,
        max_leaf_size = leaf_type::max_size
    };

private:
    key_compare key_compare_;
    mutable node_cache_type node_cache_;
    mutable leaf_cache_type leaf_cache_;
    iterator_map_type iterator_map_;
    size_type size_;
    unsigned int height_;
    bool prefetching_enabled_;
    block_manager* bm_;
    alloc_strategy_type alloc_strategy_;

    typedef std::map<key_type, node_bid_type, key_compare> root_node_type;
    typedef typename root_node_type::iterator root_node_iterator_type;
    typedef typename root_node_type::const_iterator root_node_const_iterator_type;
    typedef std::pair<key_type, node_bid_type> root_node_pair_type;


    root_node_type root_node_;
    iterator end_iterator;


    void insert_into_root(const std::pair<key_type, node_bid_type>& splitter)
    {
        std::pair<root_node_iterator_type, bool> result =
            root_node_.insert(splitter);
        STXXL_ASSERT(result.second == true);
        if (root_node_.size() > max_node_size)          // root overflow
        {
            STXXL_VERBOSE1("btree::insert_into_root, overflow happened, splitting");

            node_bid_type LeftBid;
            node_type* LeftNode = node_cache_.get_new_node(LeftBid);
            assert(LeftNode);
            node_bid_type RightBid;
            node_type* RightNode = node_cache_.get_new_node(RightBid);
            assert(RightNode);

            const unsigned_type old_size = root_node_.size();
            const unsigned_type half = root_node_.size() / 2;
            unsigned_type i = 0;
            root_node_iterator_type it = root_node_.begin();
            typename node_block_type::iterator block_it = LeftNode->block().begin();
            while (i < half)                    // copy smaller part
            {
                *block_it = *it;
                ++i;
                ++block_it;
                ++it;
            }
            LeftNode->block().info.cur_size = (unsigned int)half;
            key_type LeftKey = (LeftNode->block()[half - 1]).first;

            block_it = RightNode->block().begin();
            while (i < old_size)                // copy larger part
            {
                *block_it = *it;
                ++i;
                ++block_it;
                ++it;
            }
            unsigned_type right_size = RightNode->block().info.cur_size = (unsigned int)(old_size - half);
            key_type RightKey = (RightNode->block()[right_size - 1]).first;

            assert(old_size == RightNode->size() + LeftNode->size());

            // create new root node
            root_node_.clear();
            root_node_.insert(root_node_pair_type(LeftKey, LeftBid));
            root_node_.insert(root_node_pair_type(RightKey, RightBid));


            ++height_;
            STXXL_VERBOSE1("btree Increasing height to " << height_);
            if (node_cache_.size() < (height_ - 1))
            {
                STXXL_THROW2(std::runtime_error, "btree::bulk_construction", "The height of the tree (" << height_ << ") has exceeded the required capacity (" << (node_cache_.size() + 1) << ") of the node cache. Increase the node cache size.");
            }
        }
    }

    template <class CacheType>
    void fuse_or_balance(root_node_iterator_type UIt, CacheType& cache_)
    {
        typedef typename CacheType::node_type local_node_type;
        typedef typename local_node_type::bid_type local_bid_type;

        root_node_iterator_type leftIt, rightIt;
        if (UIt->first == key_compare::max_value())             // UIt is the last entry in the root
        {
            assert(UIt != root_node_.begin());
            rightIt = UIt;
            leftIt = --UIt;
        }
        else
        {
            leftIt = UIt;
            rightIt = ++UIt;
            assert(rightIt != root_node_.end());
        }

        // now fuse or balance nodes pointed by leftIt and rightIt
        local_bid_type LeftBid = (local_bid_type)leftIt->second;
        local_bid_type RightBid = (local_bid_type)rightIt->second;
        local_node_type* LeftNode = cache_.get_node(LeftBid, true);
        local_node_type* RightNode = cache_.get_node(RightBid, true);

        const unsigned_type TotalSize = LeftNode->size() + RightNode->size();
        if (TotalSize <= RightNode->max_nelements())
        {
            // fuse
            RightNode->fuse(*LeftNode);                 // add the content of LeftNode to RightNode

            cache_.unfix_node(RightBid);
            cache_.delete_node(LeftBid);                // 'delete_node' unfixes LeftBid also

            root_node_.erase(leftIt);                   // delete left BID from the root
        }
        else
        {
            // balance

            key_type NewSplitter = RightNode->balance(*LeftNode);

            root_node_.erase(leftIt);                   // delete left BID from the root
            // reinsert with the new key
            root_node_.insert(root_node_pair_type(NewSplitter, (node_bid_type)LeftBid));

            cache_.unfix_node(LeftBid);
            cache_.unfix_node(RightBid);
        }
    }

    void create_empty_leaf()
    {
        leaf_bid_type NewBid;
        leaf_type* NewLeaf = leaf_cache_.get_new_node(NewBid);
        assert(NewLeaf);
        end_iterator = NewLeaf->end();                  // initialize end() iterator
        root_node_.insert(root_node_pair_type(key_compare::max_value(), (node_bid_type)NewBid));
    }

    void deallocate_children()
    {
        if (height_ == 2)
        {
            // we have children leaves here
            root_node_const_iterator_type it = root_node_.begin();
            for ( ; it != root_node_.end(); ++it)
            {
                // delete from leaf cache and deallocate bid
                leaf_cache_.delete_node((leaf_bid_type)it->second);
            }
        }
        else
        {
            root_node_const_iterator_type it = root_node_.begin();
            for ( ; it != root_node_.end(); ++it)
            {
                node_type* Node = node_cache_.get_node((node_bid_type)it->second);
                assert(Node);
                Node->deallocate_children(height_ - 1);
                // delete from node cache and deallocate bid
                node_cache_.delete_node((node_bid_type)it->second);
            }
        }
    }

    template <class InputIterator>
    void bulk_construction(InputIterator b, InputIterator e, double node_fill_factor, double leaf_fill_factor)
    {
        assert(node_fill_factor >= 0.5);
        assert(leaf_fill_factor >= 0.5);
        key_type lastKey = key_compare::max_value();

        typedef std::pair<key_type, node_bid_type> key_bid_pair;
        typedef typename stxxl::VECTOR_GENERATOR<key_bid_pair, 1, 1,
                                                 node_block_type::raw_size>::result key_bid_vector_type;

        key_bid_vector_type Bids;

        leaf_bid_type NewBid;
        leaf_type* Leaf = leaf_cache_.get_new_node(NewBid);
        const unsigned_type max_leaf_elements = unsigned_type(double(Leaf->max_nelements()) * leaf_fill_factor);

        while (b != e)
        {
            // write data in leaves

            // if *b not equal to the last element
            if (key_compare_(b->first, lastKey) || key_compare_(lastKey, b->first))
            {
                ++size_;
                if (Leaf->size() == max_leaf_elements)
                {
                    // overflow, need a new block
                    Bids.push_back(key_bid_pair(Leaf->back().first, (node_bid_type)NewBid));

                    leaf_type* NewLeaf = leaf_cache_.get_new_node(NewBid);
                    assert(NewLeaf);
                    // Setting links
                    Leaf->succ() = NewLeaf->my_bid();
                    NewLeaf->pred() = Leaf->my_bid();

                    Leaf = NewLeaf;
                }
                Leaf->push_back(*b);
                lastKey = b->first;
            }
            ++b;
        }

        // rebalance the last leaf
        if (Leaf->underflows() && !Bids.empty())
        {
            leaf_type* LeftLeaf = leaf_cache_.get_node((leaf_bid_type)(Bids.back().second));
            assert(LeftLeaf);
            if (LeftLeaf->size() + Leaf->size() <= Leaf->max_nelements())     // can fuse
            {
                Leaf->fuse(*LeftLeaf);
                leaf_cache_.delete_node((leaf_bid_type)(Bids.back().second));
                Bids.pop_back();
                assert(!Leaf->overflows() && !Leaf->underflows());
            }
            else
            {
                // need to rebalance
                const key_type NewSplitter = Leaf->balance(*LeftLeaf);
                Bids.back().first = NewSplitter;
                assert(!LeftLeaf->overflows() && !LeftLeaf->underflows());
            }
        }

        assert(!Leaf->overflows() && (!Leaf->underflows() || size_ <= max_leaf_size));

        end_iterator = Leaf->end();                 // initialize end() iterator

        Bids.push_back(key_bid_pair(key_compare::max_value(), (node_bid_type)NewBid));

        const unsigned_type max_node_elements = unsigned_type(double(max_node_size) * node_fill_factor);

        while (Bids.size() > max_node_elements)
        {
            key_bid_vector_type ParentBids;

            stxxl::uint64 nparents = div_ceil(Bids.size(), max_node_elements);
            assert(nparents >= 2);
            STXXL_VERBOSE1("btree bulk constructBids.size() " << Bids.size() << " nparents: " << nparents << " max_ns: "
                                                              << max_node_elements);
            STXXL_UNUSED(nparents);
            typename key_bid_vector_type::const_iterator it = Bids.begin();

            do
            {
                node_bid_type NewBid;
                node_type* Node = node_cache_.get_new_node(NewBid);
                assert(Node);
                unsigned_type cnt = 0;
                for ( ; cnt < max_node_elements && it != Bids.end(); ++cnt, ++it)
                {
                    Node->push_back(*it);
                }
                STXXL_VERBOSE1("btree bulk construct Node size : " << Node->size() << " limits: " <<
                               Node->min_nelements() << " " << Node->max_nelements() << " max_node_elements: " << max_node_elements);

                if (Node->underflows())
                {
                    assert(it == Bids.end());                           // this can happen only at the end
                    assert(!ParentBids.empty());

                    node_type* LeftNode = node_cache_.get_node(ParentBids.back().second);
                    assert(LeftNode);
                    if (LeftNode->size() + Node->size() <= Node->max_nelements())     // can fuse
                    {
                        Node->fuse(*LeftNode);
                        node_cache_.delete_node(ParentBids.back().second);
                        ParentBids.pop_back();
                    }
                    else
                    {       // need to rebalance
                        const key_type NewSplitter = Node->balance(*LeftNode);
                        ParentBids.back().first = NewSplitter;
                        assert(!LeftNode->overflows() && !LeftNode->underflows());
                    }
                }
                assert(!Node->overflows() && !Node->underflows());

                ParentBids.push_back(key_bid_pair(Node->back().first, NewBid));
            } while (it != Bids.end());

            std::swap(ParentBids, Bids);

            assert(nparents == Bids.size() || (nparents - 1) == Bids.size());

            ++height_;
            STXXL_VERBOSE1("Increasing height to " << height_);
            if (node_cache_.size() < (height_ - 1))
            {
                STXXL_THROW2(std::runtime_error, "btree::bulk_construction", "The height of the tree (" << height_ << ") has exceeded the required capacity (" << (node_cache_.size() + 1) << ") of the node cache. Increase the node cache size.");
            }
        }

        root_node_.insert(Bids.begin(), Bids.end());
    }

public:
    btree(unsigned_type node_cache_size_in_bytes,
          unsigned_type leaf_cache_size_in_bytes
          ) :
        node_cache_(node_cache_size_in_bytes, this, key_compare_),
        leaf_cache_(leaf_cache_size_in_bytes, this, key_compare_),
        iterator_map_(this),
        size_(0),
        height_(2),
        prefetching_enabled_(true),
        bm_(block_manager::get_instance())
    {
        STXXL_VERBOSE1("Creating a btree, addr=" << this);
        STXXL_VERBOSE1(" bytes in a node: " << node_bid_type::size);
        STXXL_VERBOSE1(" bytes in a leaf: " << leaf_bid_type::size);
        STXXL_VERBOSE1(" elements in a node: " << node_block_type::size);
        STXXL_VERBOSE1(" elements in a leaf: " << leaf_block_type::size);
        STXXL_VERBOSE1(" size of a node element: " << sizeof(typename node_block_type::value_type));
        STXXL_VERBOSE1(" size of a leaf element: " << sizeof(typename leaf_block_type::value_type));


        create_empty_leaf();
    }

    btree(const key_compare& c_,
          unsigned_type node_cache_size_in_bytes,
          unsigned_type leaf_cache_size_in_bytes
          ) :
        key_compare_(c_),
        node_cache_(node_cache_size_in_bytes, this, key_compare_),
        leaf_cache_(leaf_cache_size_in_bytes, this, key_compare_),
        iterator_map_(this),
        size_(0),
        height_(2),
        prefetching_enabled_(true),
        bm_(block_manager::get_instance())
    {
        STXXL_VERBOSE1("Creating a btree, addr=" << this);
        STXXL_VERBOSE1(" bytes in a node: " << node_bid_type::size);
        STXXL_VERBOSE1(" bytes in a leaf: " << leaf_bid_type::size);

        create_empty_leaf();
    }

    virtual ~btree()
    {
        try
        {
            deallocate_children();
        } catch (...)
        {
            // no exceptions in destructor
        }
    }

    size_type size() const
    {
        return size_;
    }

    size_type max_size() const
    {
        return std::numeric_limits<size_type>::max();
    }

    bool empty() const
    {
        return !size_;
    }

    std::pair<iterator, bool> insert(const value_type& x)
    {
        root_node_iterator_type it = root_node_.lower_bound(x.first);
        assert(!root_node_.empty());
        assert(it != root_node_.end());
        if (height_ == 2)                // 'it' points to a leaf
        {
            STXXL_VERBOSE1("Inserting new value into a leaf");
            leaf_type* Leaf = leaf_cache_.get_node((leaf_bid_type)it->second, true);
            assert(Leaf);
            std::pair<key_type, leaf_bid_type> Splitter;
            std::pair<iterator, bool> result = Leaf->insert(x, Splitter);
            if (result.second)
                ++size_;

            leaf_cache_.unfix_node((leaf_bid_type)it->second);
            //if(key_compare::max_value() == Splitter.first)
            if (!(key_compare_(key_compare::max_value(), Splitter.first) ||
                  key_compare_(Splitter.first, key_compare::max_value())))
                return result;
            // no overflow/splitting happened

            STXXL_VERBOSE1("Inserting new value into root node");

            insert_into_root(std::make_pair(Splitter.first, node_bid_type(Splitter.second)));

            assert(leaf_cache_.nfixed() == 0);
            assert(node_cache_.nfixed() == 0);
            return result;
        }

        // 'it' points to a node
        STXXL_VERBOSE1("Inserting new value into a node");
        node_type* Node = node_cache_.get_node((node_bid_type)it->second, true);
        assert(Node);
        std::pair<key_type, node_bid_type> Splitter;
        std::pair<iterator, bool> result = Node->insert(x, height_ - 1, Splitter);
        if (result.second)
            ++size_;

        node_cache_.unfix_node((node_bid_type)it->second);
        //if(key_compare::max_value() == Splitter.first)
        if (!(key_compare_(key_compare::max_value(), Splitter.first) ||
              key_compare_(Splitter.first, key_compare::max_value())))
            return result;
        // no overflow/splitting happened

        STXXL_VERBOSE1("Inserting new value into root node");

        insert_into_root(Splitter);

        assert(leaf_cache_.nfixed() == 0);
        assert(node_cache_.nfixed() == 0);

        return result;
    }

    iterator begin()
    {
        root_node_iterator_type it = root_node_.begin();
        assert(it != root_node_.end());

        if (height_ == 2)                // 'it' points to a leaf
        {
            STXXL_VERBOSE1("btree: retrieving begin() from the first leaf");
            leaf_type* Leaf = leaf_cache_.get_node((leaf_bid_type)it->second);
            assert(Leaf);

            assert(leaf_cache_.nfixed() == 0);
            assert(node_cache_.nfixed() == 0);
            return Leaf->begin();
        }

        // 'it' points to a node
        STXXL_VERBOSE1("btree: retrieving begin() from the first node");
        node_type* Node = node_cache_.get_node((node_bid_type)it->second, true);
        assert(Node);
        iterator result = Node->begin(height_ - 1);
        node_cache_.unfix_node((node_bid_type)it->second);

        assert(leaf_cache_.nfixed() == 0);
        assert(node_cache_.nfixed() == 0);

        return result;
    }

    const_iterator begin() const
    {
        root_node_const_iterator_type it = root_node_.begin();
        assert(it != root_node_.end());

        if (height_ == 2)                // 'it' points to a leaf
        {
            STXXL_VERBOSE1("btree: retrieving begin() from the first leaf");
            leaf_type const* Leaf = leaf_cache_.get_const_node((leaf_bid_type)it->second);
            assert(Leaf);
            assert(leaf_cache_.nfixed() == 0);
            assert(node_cache_.nfixed() == 0);
            return Leaf->begin();
        }

        // 'it' points to a node
        STXXL_VERBOSE1("btree: retrieving begin() from the first node");
        node_type const* Node = node_cache_.get_const_node((node_bid_type)it->second, true);
        assert(Node);
        const_iterator result = Node->begin(height_ - 1);
        node_cache_.unfix_node((node_bid_type)it->second);
        assert(leaf_cache_.nfixed() == 0);
        assert(node_cache_.nfixed() == 0);
        return result;
    }

    iterator end()
    {
        return end_iterator;
    }

    const_iterator end() const
    {
        return end_iterator;
    }

    data_type& operator [] (const key_type& k)
    {
        return (*((insert(value_type(k, data_type()))).first)).second;
    }

    iterator find(const key_type& k)
    {
        root_node_iterator_type it = root_node_.lower_bound(k);
        assert(it != root_node_.end());

        if (height_ == 2)                // 'it' points to a leaf
        {
            STXXL_VERBOSE1("Searching in a leaf");
            leaf_type* Leaf = leaf_cache_.get_node((leaf_bid_type)it->second, true);
            assert(Leaf);
            iterator result = Leaf->find(k);
            leaf_cache_.unfix_node((leaf_bid_type)it->second);
            assert(result == end() || result->first == k);
            assert(leaf_cache_.nfixed() == 0);
            assert(node_cache_.nfixed() == 0);
            return result;
        }

        // 'it' points to a node
        STXXL_VERBOSE1("Searching in a node");
        node_type* Node = node_cache_.get_node((node_bid_type)it->second, true);
        assert(Node);
        iterator result = Node->find(k, height_ - 1);
        node_cache_.unfix_node((node_bid_type)it->second);

        assert(result == end() || result->first == k);
        assert(leaf_cache_.nfixed() == 0);
        assert(node_cache_.nfixed() == 0);
        return result;
    }

    const_iterator find(const key_type& k) const
    {
        root_node_const_iterator_type it = root_node_.lower_bound(k);
        assert(it != root_node_.end());

        if (height_ == 2)                // 'it' points to a leaf
        {
            STXXL_VERBOSE1("Searching in a leaf");
            leaf_type const* Leaf = leaf_cache_.get_const_node((leaf_bid_type)it->second, true);
            assert(Leaf);
            const_iterator result = Leaf->find(k);
            leaf_cache_.unfix_node((leaf_bid_type)it->second);
            assert(result == end() || result->first == k);
            assert(leaf_cache_.nfixed() == 0);
            assert(node_cache_.nfixed() == 0);
            return result;
        }

        // 'it' points to a node
        STXXL_VERBOSE1("Searching in a node");
        node_type const* Node = node_cache_.get_const_node((node_bid_type)it->second, true);
        assert(Node);
        const_iterator result = Node->find(k, height_ - 1);
        node_cache_.unfix_node((node_bid_type)it->second);

        assert(result == end() || result->first == k);
        assert(leaf_cache_.nfixed() == 0);
        assert(node_cache_.nfixed() == 0);
        return result;
    }

    iterator lower_bound(const key_type& k)
    {
        root_node_iterator_type it = root_node_.lower_bound(k);
        assert(it != root_node_.end());

        if (height_ == 2)                // 'it' points to a leaf
        {
            STXXL_VERBOSE1("Searching lower bound in a leaf");
            leaf_type* Leaf = leaf_cache_.get_node((leaf_bid_type)it->second, true);
            assert(Leaf);
            iterator result = Leaf->lower_bound(k);
            leaf_cache_.unfix_node((leaf_bid_type)it->second);
            assert(leaf_cache_.nfixed() == 0);
            assert(node_cache_.nfixed() == 0);
            return result;
        }

        // 'it' points to a node
        STXXL_VERBOSE1("Searching lower bound in a node");
        node_type* Node = node_cache_.get_node((node_bid_type)it->second, true);
        assert(Node);
        iterator result = Node->lower_bound(k, height_ - 1);
        node_cache_.unfix_node((node_bid_type)it->second);

        assert(leaf_cache_.nfixed() == 0);
        assert(node_cache_.nfixed() == 0);
        return result;
    }

    const_iterator lower_bound(const key_type& k) const
    {
        root_node_const_iterator_type it = root_node_.lower_bound(k);
        assert(it != root_node_.end());

        if (height_ == 2)                // 'it' points to a leaf
        {
            STXXL_VERBOSE1("Searching lower bound in a leaf");
            leaf_type const* Leaf = leaf_cache_.get_const_node((leaf_bid_type)it->second, true);
            assert(Leaf);
            const_iterator result = Leaf->lower_bound(k);
            leaf_cache_.unfix_node((leaf_bid_type)it->second);

            assert(leaf_cache_.nfixed() == 0);
            assert(node_cache_.nfixed() == 0);
            return result;
        }

        // 'it' points to a node
        STXXL_VERBOSE1("Searching lower bound in a node");
        node_type const* Node = node_cache_.get_const_node((node_bid_type)it->second, true);
        assert(Node);
        const_iterator result = Node->lower_bound(k, height_ - 1);
        node_cache_.unfix_node((node_bid_type)it->second);

        assert(leaf_cache_.nfixed() == 0);
        assert(node_cache_.nfixed() == 0);
        return result;
    }

    iterator upper_bound(const key_type& k)
    {
        root_node_iterator_type it = root_node_.upper_bound(k);
        assert(it != root_node_.end());

        if (height_ == 2)                // 'it' points to a leaf
        {
            STXXL_VERBOSE1("Searching upper bound in a leaf");
            leaf_type* Leaf = leaf_cache_.get_node((leaf_bid_type)it->second, true);
            assert(Leaf);
            iterator result = Leaf->upper_bound(k);
            leaf_cache_.unfix_node((leaf_bid_type)it->second);

            assert(leaf_cache_.nfixed() == 0);
            assert(node_cache_.nfixed() == 0);
            return result;
        }

        // 'it' points to a node
        STXXL_VERBOSE1("Searching upper bound in a node");
        node_type* Node = node_cache_.get_node((node_bid_type)it->second, true);
        assert(Node);
        iterator result = Node->upper_bound(k, height_ - 1);
        node_cache_.unfix_node((node_bid_type)it->second);

        assert(leaf_cache_.nfixed() == 0);
        assert(node_cache_.nfixed() == 0);
        return result;
    }

    const_iterator upper_bound(const key_type& k) const
    {
        root_node_const_iterator_type it = root_node_.upper_bound(k);
        assert(it != root_node_.end());

        if (height_ == 2)                // 'it' points to a leaf
        {
            STXXL_VERBOSE1("Searching upper bound in a leaf");
            leaf_type const* Leaf = leaf_cache_.get_const_node((leaf_bid_type)it->second, true);
            assert(Leaf);
            const_iterator result = Leaf->upper_bound(k);
            leaf_cache_.unfix_node((leaf_bid_type)it->second);

            assert(leaf_cache_.nfixed() == 0);
            assert(node_cache_.nfixed() == 0);
            return result;
        }

        // 'it' points to a node
        STXXL_VERBOSE1("Searching upper bound in a node");
        node_type const* Node = node_cache_.get_const_node((node_bid_type)it->second, true);
        assert(Node);
        const_iterator result = Node->upper_bound(k, height_ - 1);
        node_cache_.unfix_node((node_bid_type)it->second);

        assert(leaf_cache_.nfixed() == 0);
        assert(node_cache_.nfixed() == 0);
        return result;
    }

    std::pair<iterator, iterator> equal_range(const key_type& k)
    {
        iterator l = lower_bound(k);                                    // l->first >= k

        if (l == end() || key_compare_(k, l->first))                    // if (k < l->first)
            return std::pair<iterator, iterator>(l, l);
        // then upper_bound == lower_bound

        iterator u = l;
        ++u;                                                            // only one element ==k can exist

        assert(leaf_cache_.nfixed() == 0);
        assert(node_cache_.nfixed() == 0);

        return std::pair<iterator, iterator>(l, u);                     // then upper_bound == (lower_bound+1)
    }

    std::pair<const_iterator, const_iterator> equal_range(const key_type& k) const
    {
        const_iterator l = lower_bound(k);                              // l->first >= k

        if (l == end() || key_compare_(k, l->first))                    // if (k < l->first)
            return std::pair<const_iterator, const_iterator>(l, l);
        // then upper_bound == lower_bound

        const_iterator u = l;
        ++u;                                                            // only one element ==k can exist

        assert(leaf_cache_.nfixed() == 0);
        assert(node_cache_.nfixed() == 0);
        return std::pair<const_iterator, const_iterator>(l, u);         // then upper_bound == (lower_bound+1)
    }

    size_type erase(const key_type& k)
    {
        root_node_iterator_type it = root_node_.lower_bound(k);
        assert(it != root_node_.end());
        if (height_ == 2)                // 'it' points to a leaf
        {
            STXXL_VERBOSE1("Deleting key from a leaf");
            leaf_type* Leaf = leaf_cache_.get_node((leaf_bid_type)it->second, true);
            assert(Leaf);
            size_type result = Leaf->erase(k);
            size_ -= result;
            leaf_cache_.unfix_node((leaf_bid_type)it->second);
            assert(leaf_cache_.nfixed() == 0);
            assert(node_cache_.nfixed() == 0);

            if ((!Leaf->underflows()) || root_node_.size() == 1)
                return result;
            // no underflow or root has a special degree 1 (too few elements)

            STXXL_VERBOSE1("btree: Fusing or rebalancing a leaf");
            fuse_or_balance(it, leaf_cache_);

            assert(leaf_cache_.nfixed() == 0);
            assert(node_cache_.nfixed() == 0);

            return result;
        }

        // 'it' points to a node
        STXXL_VERBOSE1("Deleting key from a node");
        assert(root_node_.size() >= 2);
        node_type* Node = node_cache_.get_node((node_bid_type)it->second, true);
        assert(Node);
        size_type result = Node->erase(k, height_ - 1);
        size_ -= result;
        node_cache_.unfix_node((node_bid_type)it->second);
        assert(leaf_cache_.nfixed() == 0);
        assert(node_cache_.nfixed() == 0);
        if (!Node->underflows())
            return result;
        // no underflow happened

        STXXL_VERBOSE1("Fusing or rebalancing a node");
        fuse_or_balance(it, node_cache_);

        if (root_node_.size() == 1)
        {
            STXXL_VERBOSE1("btree Root has size 1 and height > 2");
            STXXL_VERBOSE1("btree Deallocate root and decrease height");
            it = root_node_.begin();
            node_bid_type RootBid = it->second;
            assert(it->first == key_compare::max_value());
            node_type* RootNode = node_cache_.get_node(RootBid);
            assert(RootNode);
            assert(RootNode->back().first == key_compare::max_value());
            root_node_.clear();
            root_node_.insert(RootNode->block().begin(),
                              RootNode->block().begin() + RootNode->size());

            node_cache_.delete_node(RootBid);
            --height_;
            STXXL_VERBOSE1("btree Decreasing height to " << height_);
        }

        assert(leaf_cache_.nfixed() == 0);
        assert(node_cache_.nfixed() == 0);

        return result;
    }

    size_type count(const key_type& k)
    {
        if (find(k) == end())
            return 0;

        return 1;
    }

    void erase(iterator pos)
    {
        assert(pos != end());
#ifndef NDEBUG
        size_type old_size = size();
#endif

        erase(pos->first);

        assert(size() == old_size - 1);
    }

    iterator insert(iterator /*pos*/, const value_type& x)
    {
        return insert(x).first;                 // pos ignored in the current version
    }

    void clear()
    {
        deallocate_children();

        root_node_.clear();

        size_ = 0;
        height_ = 2,

        create_empty_leaf();
        assert(leaf_cache_.nfixed() == 0);
        assert(node_cache_.nfixed() == 0);
    }

    template <class InputIterator>
    void insert(InputIterator b, InputIterator e)
    {
        while (b != e)
        {
            insert(*(b++));
        }
    }

    template <class InputIterator>
    btree(InputIterator b,
          InputIterator e,
          const key_compare& c_,
          unsigned_type node_cache_size_in_bytes,
          unsigned_type leaf_cache_size_in_bytes,
          bool range_sorted = false,
          double node_fill_factor = 0.75,
          double leaf_fill_factor = 0.6
          ) :
        key_compare_(c_),
        node_cache_(node_cache_size_in_bytes, this, key_compare_),
        leaf_cache_(leaf_cache_size_in_bytes, this, key_compare_),
        iterator_map_(this),
        size_(0),
        height_(2),
        prefetching_enabled_(true),
        bm_(block_manager::get_instance())
    {
        STXXL_VERBOSE1("Creating a btree, addr=" << this);
        STXXL_VERBOSE1(" bytes in a node: " << node_bid_type::size);
        STXXL_VERBOSE1(" bytes in a leaf: " << leaf_bid_type::size);

        if (range_sorted == false)
        {
            create_empty_leaf();
            insert(b, e);
            assert(leaf_cache_.nfixed() == 0);
            assert(node_cache_.nfixed() == 0);
            return;
        }

        bulk_construction(b, e, node_fill_factor, leaf_fill_factor);
        assert(leaf_cache_.nfixed() == 0);
        assert(node_cache_.nfixed() == 0);
    }


    template <class InputIterator>
    btree(InputIterator b,
          InputIterator e,
          unsigned_type node_cache_size_in_bytes,
          unsigned_type leaf_cache_size_in_bytes,
          bool range_sorted = false,
          double node_fill_factor = 0.75,
          double leaf_fill_factor = 0.6
          ) :
        node_cache_(node_cache_size_in_bytes, this, key_compare_),
        leaf_cache_(leaf_cache_size_in_bytes, this, key_compare_),
        iterator_map_(this),
        size_(0),
        height_(2),
        prefetching_enabled_(true),
        bm_(block_manager::get_instance())
    {
        STXXL_VERBOSE1("Creating a btree, addr=" << this);
        STXXL_VERBOSE1(" bytes in a node: " << node_bid_type::size);
        STXXL_VERBOSE1(" bytes in a leaf: " << leaf_bid_type::size);

        if (range_sorted == false)
        {
            create_empty_leaf();
            insert(b, e);
            assert(leaf_cache_.nfixed() == 0);
            assert(node_cache_.nfixed() == 0);
            return;
        }

        bulk_construction(b, e, node_fill_factor, leaf_fill_factor);
        assert(leaf_cache_.nfixed() == 0);
        assert(node_cache_.nfixed() == 0);
    }

    void erase(iterator first, iterator last)
    {
        if (first == begin() && last == end())
            clear();

        else
            while (first != last)
                erase(first++);
    }

    key_compare key_comp() const
    {
        return key_compare_;
    }
    value_compare value_comp() const
    {
        return value_compare(key_compare_);
    }

    void swap(btree& obj)
    {
        std::swap(key_compare_, obj.key_compare_);              // OK

        std::swap(node_cache_, obj.node_cache_);                // OK
        std::swap(leaf_cache_, obj.leaf_cache_);                // OK


        std::swap(iterator_map_, obj.iterator_map_);            // must update all iterators

        std::swap(end_iterator, obj.end_iterator);
        std::swap(size_, obj.size_);
        std::swap(height_, obj.height_);
        std::swap(alloc_strategy_, obj.alloc_strategy_);
        std::swap(root_node_, obj.root_node_);
    }

    void enable_prefetching()
    {
        prefetching_enabled_ = true;
    }
    void disable_prefetching()
    {
        prefetching_enabled_ = false;
    }
    bool prefetching_enabled()
    {
        return prefetching_enabled_;
    }

    void print_statistics(std::ostream& o) const
    {
        o << "Node cache statistics:" << std::endl;
        node_cache_.print_statistics(o);
        o << "Leaf cache statistics:" << std::endl;
        leaf_cache_.print_statistics(o);
    }
    void reset_statistics()
    {
        node_cache_.reset_statistics();
        leaf_cache_.reset_statistics();
    }
};

template <class KeyType,
          class DataType,
          class CompareType,
          unsigned LogNodeSize,
          unsigned LogLeafSize,
          class PDAllocStrategy
          >
inline bool operator == (const btree<KeyType, DataType, CompareType, LogNodeSize, LogLeafSize, PDAllocStrategy>& a,
                         const btree<KeyType, DataType, CompareType, LogNodeSize, LogLeafSize, PDAllocStrategy>& b)
{
    return a.size() == b.size() && std::equal(a.begin(), a.end(), b.begin());
}

template <class KeyType,
          class DataType,
          class CompareType,
          unsigned LogNodeSize,
          unsigned LogLeafSize,
          class PDAllocStrategy
          >
inline bool operator != (const btree<KeyType, DataType, CompareType, LogNodeSize, LogLeafSize, PDAllocStrategy>& a,
                         const btree<KeyType, DataType, CompareType, LogNodeSize, LogLeafSize, PDAllocStrategy>& b)
{
    return !(a == b);
}


template <class KeyType,
          class DataType,
          class CompareType,
          unsigned LogNodeSize,
          unsigned LogLeafSize,
          class PDAllocStrategy
          >
inline bool operator < (const btree<KeyType, DataType, CompareType, LogNodeSize, LogLeafSize, PDAllocStrategy>& a,
                        const btree<KeyType, DataType, CompareType, LogNodeSize, LogLeafSize, PDAllocStrategy>& b)
{
    return std::lexicographical_compare(a.begin(), a.end(), b.begin(), b.end());
}


template <class KeyType,
          class DataType,
          class CompareType,
          unsigned LogNodeSize,
          unsigned LogLeafSize,
          class PDAllocStrategy
          >
inline bool operator > (const btree<KeyType, DataType, CompareType, LogNodeSize, LogLeafSize, PDAllocStrategy>& a,
                        const btree<KeyType, DataType, CompareType, LogNodeSize, LogLeafSize, PDAllocStrategy>& b)
{
    return b < a;
}


template <class KeyType,
          class DataType,
          class CompareType,
          unsigned LogNodeSize,
          unsigned LogLeafSize,
          class PDAllocStrategy
          >
inline bool operator <= (const btree<KeyType, DataType, CompareType, LogNodeSize, LogLeafSize, PDAllocStrategy>& a,
                         const btree<KeyType, DataType, CompareType, LogNodeSize, LogLeafSize, PDAllocStrategy>& b)
{
    return !(b < a);
}

template <class KeyType,
          class DataType,
          class CompareType,
          unsigned LogNodeSize,
          unsigned LogLeafSize,
          class PDAllocStrategy
          >
inline bool operator >= (const btree<KeyType, DataType, CompareType, LogNodeSize, LogLeafSize, PDAllocStrategy>& a,
                         const btree<KeyType, DataType, CompareType, LogNodeSize, LogLeafSize, PDAllocStrategy>& b)
{
    return !(a < b);
}

} // namespace btree

STXXL_END_NAMESPACE


namespace std {

template <class KeyType,
          class DataType,
          class CompareType,
          unsigned LogNodeSize,
          unsigned LogLeafSize,
          class PDAllocStrategy
          >
void swap(stxxl::btree::btree<KeyType, DataType, CompareType, LogNodeSize, LogLeafSize, PDAllocStrategy>& a,
          stxxl::btree::btree<KeyType, DataType, CompareType, LogNodeSize, LogLeafSize, PDAllocStrategy>& b)
{
    if (&a != &b)
        a.swap(b);
}

} // namespace std

#endif // !STXXL_CONTAINERS_BTREE_BTREE_HEADER