xref: /dports/databases/percona56-client/percona-server-5.6.51-91.0/storage/tokudb/PerconaFT/util/dmt.h

/* -*- mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*- */
// vim: ft=cpp:expandtab:ts=8:sw=4:softtabstop=4:
#ident "$Id$"
/*======
This file is part of PerconaFT.


Copyright (c) 2006, 2015, Percona and/or its affiliates. All rights reserved.

    PerconaFT is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License, version 2,
    as published by the Free Software Foundation.

    PerconaFT is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with PerconaFT.  If not, see <http://www.gnu.org/licenses/>.

----------------------------------------

    PerconaFT is free software: you can redistribute it and/or modify
    it under the terms of the GNU Affero General Public License, version 3,
    as published by the Free Software Foundation.

    PerconaFT is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Affero General Public License for more details.

    You should have received a copy of the GNU Affero General Public License
    along with PerconaFT.  If not, see <http://www.gnu.org/licenses/>.
======= */

#ident "Copyright (c) 2006, 2015, Percona and/or its affiliates. All rights reserved."

#pragma once

#include <vector>

#include "portability/memory.h"
#include "portability/toku_portability.h"
#include "portability/toku_race_tools.h"
#include "portability/toku_stdint.h"

#include "ft/serialize/wbuf.h"
#include "util/growable_array.h"
#include "util/mempool.h"

namespace toku {
typedef uint32_t node_offset;


/**
 * Dynamic Order Maintenance Tree (DMT)
 *
 * Maintains a collection of totally ordered values, where each value has weight 1.
 * A DMT supports variable sized values.
 * The DMT is a mutable datatype.
 *
 * The Abstraction:
 *
 * An DMT is a vector of values, $V$, where $|V|$ is the length of the vector.
 * The vector is numbered from $0$ to $|V|-1$.
 *
 * We can create a new DMT, which is the empty vector.
 *
 * We can insert a new element $x$ into slot $i$, changing $V$ into $V'$ where
 *  $|V'|=1+|V|$       and
 *
 *   V'_j = V_j       if $j<i$
 *          x         if $j=i$
 *          V_{j-1}   if $j>i$.
 *
 * We can specify $i$ using a kind of function instead of as an integer.
 * Let $b$ be a function mapping from values to nonzero integers, such that
 * the signum of $b$ is monotically increasing.
 * We can specify $i$ as the minimum integer such that $b(V_i)>0$.
 *
 * We look up a value using its index, or using a Heaviside function.
 * For lookups, we allow $b$ to be zero for some values, and again the signum of $b$ must be monotonically increasing.
 * When lookup up values, we can look up
 *  $V_i$ where $i$ is the minimum integer such that $b(V_i)=0$.   (With a special return code if no such value exists.)
 *      (Rationale:  Ordinarily we want $i$ to be unique.  But for various reasons we want to allow multiple zeros, and we want the smallest $i$ in that case.)
 *  $V_i$ where $i$ is the minimum integer such that $b(V_i)>0$.   (Or an indication that no such value exists.)
 *  $V_i$ where $i$ is the maximum integer such that $b(V_i)<0$.   (Or an indication that no such value exists.)
 *
 * When looking up a value using a Heaviside function, we get the value and its index.
 *
 * Performance:
 *  Insertion and deletion should run with $O(\log |V|)$ time and $O(\log |V|)$ calls to the Heaviside function.
 *  The memory required is O(|V|).
 *
 * Usage:
 *  The dmt is templated by three parameters:
 *   - dmtdata_t is what will be stored within the dmt.  These could be pointers or real data types (ints, structs).
 *   - dmtdataout_t is what will be returned by find and related functions.  By default, it is the same as dmtdata_t, but you can set it to (dmtdata_t *).
 *   - dmtwriter_t is a class that effectively handles (de)serialization between the value stored in the dmt and outside the dmt.
 *  To create an dmt which will store "TXNID"s, for example, it is a good idea to typedef the template:
 *   typedef dmt<TXNID, TXNID, txnid_writer_t> txnid_dmt_t;
 *  If you are storing structs (or you want to edit what is stored), you may want to be able to get a pointer to the data actually stored in the dmt (see find_zero).  To do this, use the second template parameter:
 *   typedef dmt<struct foo, struct foo *, foo_writer_t> foo_dmt_t;
 */

namespace dmt_internal {

class subtree {
private:
    uint32_t m_index;
public:
    // The maximum mempool size for a dmt is 2**32-2
    static const uint32_t NODE_NULL = UINT32_MAX;
    inline void set_to_null(void) {
        m_index = NODE_NULL;
    }

    inline bool is_null(void) const {
        return NODE_NULL == this->get_offset();
    }

    inline node_offset get_offset(void) const {
        return m_index;
    }

    inline void set_offset(node_offset index) {
        paranoid_invariant(index != NODE_NULL);
        m_index = index;
    }
} __attribute__((__packed__,__aligned__(4)));

template<typename dmtdata_t>
class dmt_node_templated {
public:
    uint32_t weight;
    subtree left;
    subtree right;
    uint32_t value_length;
    dmtdata_t value;
} __attribute__((__aligned__(4)));  //NOTE: we cannot use attribute packed or dmtdata_t will call copy constructors (dmtdata_t might not be packed by default)

}

using namespace toku::dmt_internal;

// Each data type used in a dmt requires a dmt_writer class (allows you to insert/etc with dynamic sized types).
// A dmt_writer can be thought of a (de)serializer
// There is no default implementation.
// A dmtwriter instance handles reading/writing 'dmtdata_t's to/from the dmt.
// The class must implement the following functions:
//      The size required in a dmt for the dmtdata_t represented:
//          size_t get_size(void) const;
//      Write the dmtdata_t to memory owned by a dmt:
//          void write_to(dmtdata_t *const dest) const;
//      Constructor (others are allowed, but this one is required)
//          dmtwriter(const uint32_t dmtdata_t_len, dmtdata_t *const src)

template<typename dmtdata_t,
         typename dmtdataout_t,
         typename dmtwriter_t
        >
class dmt {
private:
    typedef dmt_node_templated<dmtdata_t> dmt_node;

public:
    static const uint8_t ALIGNMENT = 4;

    class builder {
    public:
        void append(const dmtwriter_t &value);

        // Create a dmt builder to build a dmt that will have at most n_values values and use
        // at most n_value_bytes bytes in the mempool to store values (not counting node or alignment overhead).
        void create(uint32_t n_values, uint32_t n_value_bytes);

        bool value_length_is_fixed(void);

        // Constructs a dmt that contains everything that was append()ed to this builder.
        // Destroys this builder and frees associated memory.
        void build(dmt<dmtdata_t, dmtdataout_t, dmtwriter_t> *dest);
    private:
        uint32_t max_values;
        uint32_t max_value_bytes;
        node_offset *sorted_node_offsets;
        bool temp_valid;
        dmt<dmtdata_t, dmtdataout_t, dmtwriter_t> temp;
    };

    /**
     * Effect: Create an empty DMT.
     * Performance: constant time.
     */
    void create(void);

    /**
     * Effect: Create a DMT containing values.  The number of values is in numvalues.
     *         Each value is of a fixed (at runtime) length.
     *         mem contains the values in packed form (no alignment padding)
     *         Caller retains ownership of mem.
     * Requires: this has not been created yet
     * Rationale:    Normally to insert N values takes O(N lg N) amortized time.
     *               If the N values are known in advance, are sorted, and
     *               the structure is empty, we can batch insert them much faster.
     */
    __attribute__((nonnull))
    void create_from_sorted_memory_of_fixed_size_elements(
            const void *mem,
            const uint32_t numvalues,
            const uint32_t mem_length,
            const uint32_t fixed_value_length);

    /**
     * Effect: Creates a copy of an dmt.
     *  Creates this as the clone.
     *  Each element is copied directly.  If they are pointers, the underlying data is not duplicated.
     * Performance: O(memory) (essentially a memdup)
     *  The underlying structures are memcpy'd.  Only the values themselves are copied (shallow copy)
     */
    void clone(const dmt &src);

    /**
     * Effect: Set the tree to be empty.
     *  Note: Will not reallocate or resize any memory.
     *  Note: If this dmt had variable sized elements, it will start tracking again (until it gets values of two different sizes)
     * Performance: time=O(1)
     */
    void clear(void);

    /**
     * Effect:  Destroy an DMT, freeing all its memory.
     *   If the values being stored are pointers, their underlying data is not freed.
     *   Those values may be freed before or after calling ::destroy()
     * Rationale: Returns no values since free() cannot fail.
     * Rationale: Does not free the underlying pointers to reduce complexity/maintain abstraction layer
     * Performance:  time=O(1)
     */
    void destroy(void);

    /**
     * Effect: return |this| (number of values stored in this dmt).
     * Performance:  time=O(1)
     */
    uint32_t size(void) const;

    /**
     * Effect: Serialize all values contained in this dmt into a packed form (no alignment padding).
     *  We serialized to wb.  expected_unpadded_memory is the size of memory reserved in the wbuf
     *  for serialization.  (We assert that serialization requires exactly the expected amount)
     * Requires:
     *  ::prepare_for_serialize() has been called and no non-const functions have been called since.
     *  This dmt has fixed-length values and is in array form.
     * Performance:
     *  O(memory)
     */
    void serialize_values(uint32_t expected_unpadded_memory, struct wbuf *wb) const;

    /**
     * Effect:  Insert value into the DMT.
     *   If there is some i such that $h(V_i, v)=0$ then returns DB_KEYEXIST.
     *   Otherwise, let i be the minimum value such that $h(V_i, v)>0$.
     *      If no such i exists, then let i be |V|
     *   Then this has the same effect as
     *    insert_at(tree, value, i);
     *   If idx!=NULL then i is stored in *idx
     * Requires:  The signum of h must be monotonically increasing.
     * Returns:
     *    0            success
     *    DB_KEYEXIST  the key is present (h was equal to zero for some value)
     * On nonzero return, dmt is unchanged.
     * Performance: time=O(\log N) amortized.
     * Rationale: Some future implementation may be O(\log N) worst-case time, but O(\log N) amortized is good enough for now.
     */
    template<typename dmtcmp_t, int (*h)(const uint32_t size, const dmtdata_t &, const dmtcmp_t &)>
    int insert(const dmtwriter_t &value, const dmtcmp_t &v, uint32_t *const idx);

    /**
     * Effect: Increases indexes of all items at slot >= idx by 1.
     *         Insert value into the position at idx.
     * Returns:
     *   0         success
     *   EINVAL    if idx > this->size()
     * On error, dmt is unchanged.
     * Performance: time=O(\log N) amortized time.
     * Rationale: Some future implementation may be O(\log N) worst-case time, but O(\log N) amortized is good enough for now.
     */
    int insert_at(const dmtwriter_t &value, const uint32_t idx);

    /**
     * Effect: Delete the item in slot idx.
     *         Decreases indexes of all items at slot > idx by 1.
     * Returns
     *     0            success
     *     EINVAL       if idx>=this->size()
     * On error, dmt is unchanged.
     * Rationale: To delete an item, first find its index using find or find_zero, then delete it.
     * Performance: time=O(\log N) amortized.
     */
    int delete_at(const uint32_t idx);

    /**
     * Effect:  Iterate over the values of the dmt, from left to right, calling f on each value.
     *  The first argument passed to f is a ref-to-const of the value stored in the dmt.
     *  The second argument passed to f is the index of the value.
     *  The third argument passed to f is iterate_extra.
     *  The indices run from 0 (inclusive) to this->size() (exclusive).
     * Requires: f != NULL
     * Returns:
     *  If f ever returns nonzero, then the iteration stops, and the value returned by f is returned by iterate.
     *  If f always returns zero, then iterate returns 0.
     * Requires:  Don't modify the dmt while running.  (E.g., f may not insert or delete values from the dmt.)
     * Performance: time=O(i+\log N) where i is the number of times f is called, and N is the number of elements in the dmt.
     * Rationale: Although the functional iterator requires defining another function (as opposed to C++ style iterator), it is much easier to read.
     * Rationale: We may at some point use functors, but for now this is a smaller change from the old DMT.
     */
    template<typename iterate_extra_t,
             int (*f)(const uint32_t, const dmtdata_t &, const uint32_t, iterate_extra_t *const)>
    int iterate(iterate_extra_t *const iterate_extra) const;

    /**
     * Effect:  Iterate over the values of the dmt, from left to right, calling f on each value.
     *  The first argument passed to f is a ref-to-const of the value stored in the dmt.
     *  The second argument passed to f is the index of the value.
     *  The third argument passed to f is iterate_extra.
     *  The indices run from 0 (inclusive) to this->size() (exclusive).
     *  We will iterate only over [left,right)
     *
     * Requires: left <= right
     * Requires: f != NULL
     * Returns:
     *  EINVAL  if right > this->size()
     *  If f ever returns nonzero, then the iteration stops, and the value returned by f is returned by iterate_on_range.
     *  If f always returns zero, then iterate_on_range returns 0.
     * Requires:  Don't modify the dmt while running.  (E.g., f may not insert or delete values from the dmt.)
     * Performance: time=O(i+\log N) where i is the number of times f is called, and N is the number of elements in the dmt.
     * Rational: Although the functional iterator requires defining another function (as opposed to C++ style iterator), it is much easier to read.
     */
    template<typename iterate_extra_t,
             int (*f)(const uint32_t, const dmtdata_t &, const uint32_t, iterate_extra_t *const)>
    int iterate_on_range(const uint32_t left, const uint32_t right, iterate_extra_t *const iterate_extra) const;

    // Attempt to verify this dmt is well formed.  (Crashes/asserts/aborts if not well formed)
    void verify(void) const;

    /**
     * Effect:  Iterate over the values of the dmt, from left to right, calling f on each value.
     *  The first argument passed to f is a pointer to the value stored in the dmt.
     *  The second argument passed to f is the index of the value.
     *  The third argument passed to f is iterate_extra.
     *  The indices run from 0 (inclusive) to this->size() (exclusive).
     * Requires: same as for iterate()
     * Returns: same as for iterate()
     * Performance: same as for iterate()
     * Rationale: In general, most iterators should use iterate() since they should not modify the data stored in the dmt.  This function is for iterators which need to modify values (for example, free_items).
     * Rationale: We assume if you are transforming the data in place, you want to do it to everything at once, so there is not yet an iterate_on_range_ptr (but there could be).
     */
    template<typename iterate_extra_t,
             int (*f)(const uint32_t, dmtdata_t *, const uint32_t, iterate_extra_t *const)>
    void iterate_ptr(iterate_extra_t *const iterate_extra);

    /**
     * Effect: Set *value=V_idx
     * Returns
     *    0             success
     *    EINVAL        if index>=toku_dmt_size(dmt)
     * On nonzero return, *value is unchanged
     * Performance: time=O(\log N)
     */
    int fetch(const uint32_t idx, uint32_t *const value_size, dmtdataout_t *const value) const;

    /**
     * Effect:  Find the smallest i such that h(V_i, extra)>=0
     *  If there is such an i and h(V_i,extra)==0 then set *idxp=i, set *value = V_i, and return 0.
     *  If there is such an i and h(V_i,extra)>0  then set *idxp=i and return DB_NOTFOUND.
     *  If there is no such i then set *idx=this->size() and return DB_NOTFOUND.
     * Note: value is of type dmtdataout_t, which may be of type (dmtdata_t) or (dmtdata_t *) but is fixed by the instantiation.
     *  If it is the value type, then the value is copied out (even if the value type is a pointer to something else)
     *  If it is the pointer type, then *value is set to a pointer to the data within the dmt.
     *  This is determined by the type of the dmt as initially declared.
     *   If the dmt is declared as dmt<foo_t>, then foo_t's will be stored and foo_t's will be returned by find and related functions.
     *   If the dmt is declared as dmt<foo_t, foo_t *>, then foo_t's will be stored, and pointers to the stored items will be returned by find and related functions.
     * Rationale:
     *  Structs too small for malloc should be stored directly in the dmt.
     *  These structs may need to be edited as they exist inside the dmt, so we need a way to get a pointer within the dmt.
     *  Using separate functions for returning pointers and values increases code duplication and reduces type-checking.
     *  That also reduces the ability of the creator of a data structure to give advice to its future users.
     *  Slight overloading in this case seemed to provide a better API and better type checking.
     */
    template<typename dmtcmp_t,
             int (*h)(const uint32_t, const dmtdata_t &, const dmtcmp_t &)>
    int find_zero(const dmtcmp_t &extra, uint32_t *const value_size, dmtdataout_t *const value, uint32_t *const idxp) const;

    /**
     *   Effect:
     *    If direction >0 then find the smallest i such that h(V_i,extra)>0.
     *    If direction <0 then find the largest  i such that h(V_i,extra)<0.
     *    (Direction may not be equal to zero.)
     *    If value!=NULL then store V_i in *value
     *    If idxp!=NULL then store i in *idxp.
     *   Requires: The signum of h is monotically increasing.
     *   Returns
     *      0             success
     *      DB_NOTFOUND   no such value is found.
     *   On nonzero return, *value and *idxp are unchanged
     *   Performance: time=O(\log N)
     *   Rationale:
     *     Here's how to use the find function to find various things
     *       Cases for find:
     *        find first value:         ( h(v)=+1, direction=+1 )
     *        find last value           ( h(v)=-1, direction=-1 )
     *        find first X              ( h(v)=(v< x) ? -1 : 1    direction=+1 )
     *        find last X               ( h(v)=(v<=x) ? -1 : 1    direction=-1 )
     *        find X or successor to X  ( same as find first X. )
     *
     *   Rationale: To help understand heaviside functions and behavor of find:
     *    There are 7 kinds of heaviside functions.
     *    The signus of the h must be monotonically increasing.
     *    Given a function of the following form, A is the element
     *    returned for direction>0, B is the element returned
     *    for direction<0, C is the element returned for
     *    direction==0 (see find_zero) (with a return of 0), and D is the element
     *    returned for direction==0 (see find_zero) with a return of DB_NOTFOUND.
     *    If any of A, B, or C are not found, then asking for the
     *    associated direction will return DB_NOTFOUND.
     *    See find_zero for more information.
     *
     *    Let the following represent the signus of the heaviside function.
     *
     *    -...-
     *        A
     *         D
     *
     *    +...+
     *    B
     *    D
     *
     *    0...0
     *    C
     *
     *    -...-0...0
     *        AC
     *
     *    0...0+...+
     *    C    B
     *
     *    -...-+...+
     *        AB
     *         D
     *
     *    -...-0...0+...+
     *        AC    B
     */
    template<typename dmtcmp_t,
             int (*h)(const uint32_t, const dmtdata_t &, const dmtcmp_t &)>
    int find(const dmtcmp_t &extra, int direction, uint32_t *const value_size, dmtdataout_t *const value, uint32_t *const idxp) const;

    /**
     * Effect: Return the size (in bytes) of the dmt, as it resides in main memory.
     * If the data stored are pointers, don't include the size of what they all point to.
     * //TODO(leif or yoni): (maybe rename and) return memory footprint instead of allocated size
     */
    size_t memory_size(void);

    // Returns whether all values in the dmt are known to be the same size.
    // Note:
    //  There are no false positives, but false negatives are allowed.
    //  A false negative can happen if this dmt had 2 (or more) different size values,
    //  and then enough were deleted so that all the remaining ones are the same size.
    //  Once that happens, this dmt will never again return true for this function unless/until
    //  ::clear() is called
    bool value_length_is_fixed(void) const;


    // If this dmt is empty, return value is undefined.
    // else if value_length_is_fixed() then it returns the fixed length.
    // else returns 0
    uint32_t get_fixed_length(void) const;

    // Preprocesses the dmt so that serialization can happen quickly.
    // After this call, serialize_values() can be called but no other mutator function can be called in between.
    void prepare_for_serialize(void);

private:
    // Do a bit of verification that subtree and nodes act like packed c structs and do not introduce unnecessary padding for alignment.
    ENSURE_POD(subtree);
    static_assert(ALIGNMENT > 0, "ALIGNMENT <= 0");
    static_assert((ALIGNMENT & (ALIGNMENT - 1)) == 0, "ALIGNMENT not a power of 2");
    static_assert(sizeof(dmt_node) - sizeof(dmtdata_t) == __builtin_offsetof(dmt_node, value), "value is not last field in node");
    static_assert(4 * sizeof(uint32_t) == __builtin_offsetof(dmt_node, value), "dmt_node is padded");
    static_assert(__builtin_offsetof(dmt_node, value) % ALIGNMENT == 0, "dmt_node requires padding for alignment");
    ENSURE_POD(dmt_node);

    struct dmt_array {
        uint32_t num_values;
    };

    struct dmt_tree {
        subtree root;
    };

    /*
    Relationship between values_same_size, d.a.num_values, value_length, is_array:
    In an empty dmt:
        is_array is true
        value_same_size is true
        value_length is undefined
        d.a.num_values is 0
    In a non-empty array dmt:
        is_array is true
        values_same_size is true
        value_length is defined
        d.a.num_values > 0
    In a non-empty tree dmt:
        is_array = false
        value_same_size is true iff all values have been the same size since the last time the dmt turned into a tree.
        value_length is defined iff values_same_size is true
        d.a.num_values is undefined (the memory is used for the tree)
    Note that in tree form, the dmt keeps track of if all values are the same size until the first time they are not.
    'values_same_size' will not become true again (even if we change all values to be the same size)
        until/unless the dmt becomes empty, at which point it becomes an array again.
     */
    bool values_same_size;
    uint32_t value_length;  // valid iff values_same_size is true.
    struct mempool mp;
    bool is_array;
    union {
        struct dmt_array a;
        struct dmt_tree t;
    } d;

    // Returns pad bytes per element (for alignment) or 0 if not fixed length.
    uint32_t get_fixed_length_alignment_overhead(void) const;

    void verify_internal(const subtree &subtree, std::vector<bool> *touched) const;

    // Retrieves the node for a given subtree.
    // Requires: !subtree.is_null()
    dmt_node & get_node(const subtree &subtree) const;

    // Retrieves the node at a given offset in the mempool.
    dmt_node & get_node(const node_offset offset) const;

    // Returns the weight of a subtree rooted at st.
    // if st.is_null(), returns 0
    // Perf: O(1)
    uint32_t nweight(const subtree &st) const;

    // Allocates space for a node (in the mempool) and uses the dmtwriter to write the value into the node
    node_offset node_malloc_and_set_value(const dmtwriter_t &value);

    // Uses the dmtwriter to write a value into node n
    void node_set_value(dmt_node *n, const dmtwriter_t &value);

    // (mempool-)free the memory for a node
    void node_free(const subtree &st);

    // Effect: Resizes the mempool (holding the array) if necessary to hold one more item of length: this->value_length
    // Requires:
    //  This dmt is in array form (and thus this->values_same_length)
    void maybe_resize_array_for_insert(void);

    // Effect: Converts a dmt from array form to tree form.
    // Perf: O(n)
    // Note: This does not clear the 'this->values_same_size' bit
    void convert_to_tree(void);

    // Effect: Resizes the mempool holding a tree if necessary.  If value==nullptr then it may shrink if overallocated,
    //         otherwise resize only happens if there is not enough free space for an insert of value
    void maybe_resize_tree(const dmtwriter_t * value);

    // Returns true if the tree rooted at st would need rebalance after adding
    // leftmod to the left subtree and rightmod to the right subtree
    bool will_need_rebalance(const subtree &st, const int leftmod, const int rightmod) const;

    __attribute__((nonnull))
    void insert_internal(subtree *const subtreep, const dmtwriter_t &value, const uint32_t idx, subtree **const rebalance_subtree);

    template<bool with_resize>
    int insert_at_array_end(const dmtwriter_t& value_in);

    dmtdata_t * alloc_array_value_end(void);

    dmtdata_t * get_array_value(const uint32_t idx) const;

    dmtdata_t * get_array_value_internal(const struct mempool *mempool, const uint32_t idx) const;

    void convert_from_array_to_tree(void);

    void convert_from_tree_to_array(void);

    void delete_internal(subtree *const subtreep, const uint32_t idx, subtree *const subtree_replace, subtree **const rebalance_subtree);

    template<typename iterate_extra_t,
             int (*f)(const uint32_t, const dmtdata_t &, const uint32_t, iterate_extra_t *const)>
    int iterate_internal_array(const uint32_t left, const uint32_t right,
                                      iterate_extra_t *const iterate_extra) const;

    template<typename iterate_extra_t,
             int (*f)(const uint32_t, dmtdata_t *, const uint32_t, iterate_extra_t *const)>
    void iterate_ptr_internal(const uint32_t left, const uint32_t right,
                                     const subtree &subtree, const uint32_t idx,
                                     iterate_extra_t *const iterate_extra);

    template<typename iterate_extra_t,
             int (*f)(const uint32_t, dmtdata_t *, const uint32_t, iterate_extra_t *const)>
    void iterate_ptr_internal_array(const uint32_t left, const uint32_t right,
                                           iterate_extra_t *const iterate_extra);

    template<typename iterate_extra_t,
             int (*f)(const uint32_t, const dmtdata_t &, const uint32_t, iterate_extra_t *const)>
    int iterate_internal(const uint32_t left, const uint32_t right,
                                const subtree &subtree, const uint32_t idx,
                                iterate_extra_t *const iterate_extra) const;

    void fetch_internal_array(const uint32_t i, uint32_t *const value_len, dmtdataout_t *const value) const;

    void fetch_internal(const subtree &subtree, const uint32_t i, uint32_t *const value_len, dmtdataout_t *const value) const;

    __attribute__((nonnull))
    void fill_array_with_subtree_offsets(node_offset *const array, const subtree &subtree) const;

    __attribute__((nonnull))
    void rebuild_subtree_from_offsets(subtree *const subtree, const node_offset *const offsets, const uint32_t numvalues);

    __attribute__((nonnull))
    void rebalance(subtree *const subtree);

    static void copyout(uint32_t *const outlen, dmtdata_t *const out, const dmt_node *const n);

    static void copyout(uint32_t *const outlen, dmtdata_t **const out, dmt_node *const n);

    static void copyout(uint32_t *const outlen, dmtdata_t *const out, const uint32_t len, const dmtdata_t *const stored_value_ptr);

    static void copyout(uint32_t *const outlen, dmtdata_t **const out, const uint32_t len, dmtdata_t *const stored_value_ptr);

    template<typename dmtcmp_t,
             int (*h)(const uint32_t, const dmtdata_t &, const dmtcmp_t &)>
    int find_internal_zero_array(const dmtcmp_t &extra, uint32_t *const value_len, dmtdataout_t *const value, uint32_t *const idxp) const;

    template<typename dmtcmp_t,
             int (*h)(const uint32_t, const dmtdata_t &, const dmtcmp_t &)>
    int find_internal_zero(const subtree &subtree, const dmtcmp_t &extra, uint32_t *const value_len, dmtdataout_t *const value, uint32_t *const idxp) const;

    template<typename dmtcmp_t,
             int (*h)(const uint32_t, const dmtdata_t &, const dmtcmp_t &)>
    int find_internal_plus_array(const dmtcmp_t &extra, uint32_t *const value_len, dmtdataout_t *const value, uint32_t *const idxp) const;

    template<typename dmtcmp_t,
             int (*h)(const uint32_t, const dmtdata_t &, const dmtcmp_t &)>
    int find_internal_plus(const subtree &subtree, const dmtcmp_t &extra, uint32_t *const value_len, dmtdataout_t *const value, uint32_t *const idxp) const;

    template<typename dmtcmp_t,
             int (*h)(const uint32_t, const dmtdata_t &, const dmtcmp_t &)>
    int find_internal_minus_array(const dmtcmp_t &extra, uint32_t *const value_len, dmtdataout_t *const value, uint32_t *const idxp) const;

    template<typename dmtcmp_t,
             int (*h)(const uint32_t, const dmtdata_t &, const dmtcmp_t &)>
    int find_internal_minus(const subtree &subtree, const dmtcmp_t &extra, uint32_t *const value_len, dmtdataout_t *const value, uint32_t *const idxp) const;

    // Allocate memory for an array:  node_offset[num_idx] from pre-allocated contiguous free space in the mempool.
    // If there is not enough space, returns nullptr.
    node_offset* alloc_temp_node_offsets(uint32_t num_idxs);

    // Returns the aligned size of x.
    // If x % ALIGNMENT == 0, returns x
    // o.w. returns x + (ALIGNMENT - (x % ALIGNMENT))
    uint32_t align(const uint32_t x) const;
};

} // namespace toku

// include the implementation here
#include "dmt.cc"