[btree] Implement btree::remove()
This commit is contained in:
Ming-Hung Tsai
373
persistent-data/data-structures/btree-remove.tcc
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373
persistent-data/data-structures/btree-remove.tcc
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// This file is part of the thin-provisioning-tools source.
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//
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// thin-provisioning-tools is free software: you can redistribute it
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// and/or modify it under the terms of the GNU General Public License
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// as published by the Free Software Foundation, either version 3 of
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// the License, or (at your option) any later version.
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//
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// thin-provisioning-tools is distributed in the hope that it will be
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// useful, but WITHOUT ANY WARRANTY; without even the implied warranty
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// of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License along
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// with thin-provisioning-tools. If not, see
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// <http://www.gnu.org/licenses/>.
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namespace persistent_data {
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template <unsigned Levels, typename ValueTraits>
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btree_detail::shadow_child
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btree<Levels, ValueTraits>::
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create_shadow_child(internal_node &parent,
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unsigned index)
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{
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block_address b = parent.value_at(index);
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pair<write_ref, bool> p = tm_.shadow(b, validator_);
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write_ref &wr = p.first;
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btree_detail::node_type type;
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node_ref<block_traits> n = to_node<block_traits>(wr);
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if (n.get_type() == btree_detail::INTERNAL) {
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type = btree_detail::INTERNAL;
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if (p.second)
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n.inc_children(internal_rc_);
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} else {
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type = btree_detail::LEAF;
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if (p.second) {
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node_ref<ValueTraits> leaf = to_node<ValueTraits>(wr);
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leaf.inc_children(rc_);
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}
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}
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parent.set_value(index, wr.get_location());
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return btree_detail::shadow_child(wr, type);
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}
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template <unsigned Levels, typename ValueTraits>
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void
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btree<Levels, ValueTraits>::
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remove(key const &key)
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{
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using namespace btree_detail;
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block_address block = root_;
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unsigned index = 0;
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shadow_spine spine(tm_, validator_);
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bool need_remove = true;
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for (unsigned level = 0; level < Levels - 1; ++level) {
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need_remove = remove_location<block_traits>(spine, block,
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key[level], &index,
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internal_rc_);
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if (!need_remove)
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break;
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internal_node n = spine.get_node<block_traits>();
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block = n.value_at(index);
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}
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if (need_remove) {
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need_remove = remove_location<ValueTraits>(spine, block,
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key[Levels - 1], &index,
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rc_);
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if (need_remove) {
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leaf_node leaf = spine.get_node<ValueTraits>();
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leaf.delete_at(index);
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}
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}
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root_ = spine.get_root();
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}
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template <unsigned Levels, typename _>
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template <typename ValueTraits, typename RC>
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bool
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btree<Levels, _>::
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remove_location(btree_detail::shadow_spine &spine,
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block_address block,
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uint64_t key,
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unsigned *index,
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RC &leaf_rc)
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{
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using namespace btree_detail;
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unsigned i = 0;
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bool r = false;
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for (;;) {
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r = spine.step(block);
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// patch up the parent to point to the new shadow
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if (spine.has_parent()) {
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internal_node p = spine.get_parent();
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p.set_value(i, spine.get_block());
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}
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internal_node n = spine.get_node<block_traits>();
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if (n.get_type() == btree_detail::LEAF) {
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node_ref<ValueTraits> leaf = spine.get_node<ValueTraits>();
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boost::optional<unsigned> idx = leaf.exact_search(key);
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if (!idx)
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return false;
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*index = *idx;
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return true;
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}
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r = rebalance_children<ValueTraits>(spine, key);
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if (!r)
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break;
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n = spine.get_node<block_traits>();
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if (n.get_type() == btree_detail::LEAF) {
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node_ref<ValueTraits> leaf = spine.get_node<ValueTraits>();
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boost::optional<unsigned> idx = leaf.exact_search(key);
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if (!idx)
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return false;
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*index = *idx;
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return true;
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}
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i = n.lower_bound(key);
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block = n.value_at(i);
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}
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return r;
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}
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template <unsigned Levels, typename _>
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template <typename ValueTraits>
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bool
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btree<Levels, _>::
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rebalance_children(btree_detail::shadow_spine &spine, uint64_t key)
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{
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internal_node n = spine.get_node<block_traits>();
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if (n.get_nr_entries() == 1) {
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block_address b = n.value_at(0);
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read_ref child = tm_.read_lock(b, validator_);
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// FIXME: is it safe?
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::memcpy(n.raw(), child.data(), read_ref::BLOCK_SIZE);
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tm_.get_sm()->dec(child.get_location());
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return true;
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}
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int i = n.lower_bound(key);
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if (i < 0)
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return false;
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bool has_left_sibling = i > 0;
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bool has_right_sibling = static_cast<unsigned>(i) < (n.get_nr_entries() - 1);
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if (!has_left_sibling)
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rebalance2<ValueTraits>(spine, i);
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else if (!has_right_sibling)
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rebalance2<ValueTraits>(spine, i - 1);
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else
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rebalance3<ValueTraits>(spine, i - 1);
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return true;
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}
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template <unsigned Levels, typename _>
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template <typename ValueTraits>
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void
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btree<Levels, _>::
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rebalance2(btree_detail::shadow_spine &spine, unsigned left_index)
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{
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internal_node parent = spine.get_node<block_traits>();
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shadow_child left = create_shadow_child(parent, left_index);
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shadow_child right = create_shadow_child(parent, left_index + 1);
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// FIXME: ugly
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if (left.get_type() == btree_detail::INTERNAL) {
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internal_node l = left.get_node<block_traits>();
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internal_node r = right.get_node<block_traits>();
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__rebalance2(parent, l, r, left_index);
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} else {
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node_ref<ValueTraits> l = left.get_node<ValueTraits>();
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node_ref<ValueTraits> r = right.get_node<ValueTraits>();
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__rebalance2(parent, l, r, left_index);
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}
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}
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template <unsigned Levels, typename _>
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template <typename ValueTraits>
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void
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btree<Levels, _>::
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__rebalance2(internal_node &parent,
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node_ref<ValueTraits> &left,
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node_ref<ValueTraits> &right,
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unsigned left_index)
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{
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unsigned nr_left = left.get_nr_entries();
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unsigned nr_right = right.get_nr_entries();
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unsigned right_index = left_index + 1;
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unsigned threshold = 2 * (left.merge_threshold() + 1);
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if (nr_left + nr_right < threshold) {
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// Merge the right child into the left
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left.copy_entries_to_left(right, nr_right);
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left.set_nr_entries(nr_left + nr_right);
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parent.delete_at(right_index);
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tm_.get_sm()->dec(right.get_location());
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} else {
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// Rebalance
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unsigned target_left = (nr_left + nr_right) / 2;
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left.move_entries(right, nr_left - target_left);
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parent.set_key(right_index, right.key_at(0));
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}
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}
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template <unsigned Levels, typename _>
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template <typename ValueTraits>
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void
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btree<Levels, _>::
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rebalance3(btree_detail::shadow_spine &spine, unsigned left_index)
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{
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internal_node parent = spine.get_node<block_traits>();
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shadow_child left = create_shadow_child(parent, left_index);
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shadow_child center = create_shadow_child(parent, left_index + 1);
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shadow_child right = create_shadow_child(parent, left_index + 2);
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// FIXME: ugly
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if (left.get_type() == btree_detail::INTERNAL) {
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internal_node l = left.get_node<block_traits>();
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internal_node c = center.get_node<block_traits>();
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internal_node r = right.get_node<block_traits>();
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__rebalance3(parent, l, c, r, left_index);
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} else {
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node_ref<ValueTraits> l = left.get_node<ValueTraits>();
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node_ref<ValueTraits> c = center.get_node<ValueTraits>();
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node_ref<ValueTraits> r = right.get_node<ValueTraits>();
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__rebalance3(parent, l, c, r, left_index);
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}
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}
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template <unsigned Levels, typename _>
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template <typename ValueTraits>
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void
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btree<Levels, _>::
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__rebalance3(internal_node &parent,
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node_ref<ValueTraits> &left,
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node_ref<ValueTraits> ¢er,
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node_ref<ValueTraits> &right,
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unsigned left_index)
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{
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unsigned nr_left = left.get_nr_entries();
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unsigned nr_center = center.get_nr_entries();
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unsigned nr_right = right.get_nr_entries();
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unsigned threshold = left.merge_threshold() * 4 + 1;
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if ((nr_left + nr_center + nr_right) < threshold)
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delete_center_node(parent, left, center, right, left_index);
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else
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redistribute3(parent, left, center, right, left_index);
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}
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template <unsigned Levels, typename _>
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template <typename ValueTraits>
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void
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btree<Levels, _>::
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delete_center_node(internal_node &parent,
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node_ref<ValueTraits> &left,
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node_ref<ValueTraits> ¢er,
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node_ref<ValueTraits> &right,
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unsigned left_index)
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{
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unsigned center_index = left_index + 1;
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unsigned right_index = left_index + 2;
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unsigned max_entries = left.get_max_entries();
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unsigned nr_left = left.get_nr_entries();
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unsigned nr_center = center.get_nr_entries();
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unsigned nr_right = right.get_nr_entries();
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unsigned shift = std::min(max_entries - nr_left, nr_center);
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if (nr_left + shift > max_entries)
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throw std::runtime_error("too many entries");
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left.copy_entries_to_left(center, shift);
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left.set_nr_entries(nr_left + shift);
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if (shift != nr_center) {
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shift = nr_center - shift;
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if ((nr_right + shift) > max_entries)
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throw std::runtime_error("too many entries");
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right.shift_entries_right(shift);
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center.copy_entries_to_right(right, shift);
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right.set_nr_entries(nr_right + shift);
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}
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parent.set_key(right_index, right.key_at(0));
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parent.delete_at(center_index);
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--right_index;
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tm_.get_sm()->dec(center.get_location());
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__rebalance2(parent, left, right, left_index);
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}
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template <unsigned Levels, typename _>
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template <typename ValueTraits>
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void
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btree<Levels, _>::
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redistribute3(internal_node &parent,
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node_ref<ValueTraits> &left,
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node_ref<ValueTraits> ¢er,
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node_ref<ValueTraits> &right,
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unsigned left_index)
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{
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unsigned center_index = left_index + 1;
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unsigned right_index = left_index + 2;
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unsigned nr_left = left.get_nr_entries();
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unsigned nr_center = center.get_nr_entries();
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unsigned nr_right = right.get_nr_entries();
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unsigned max_entries = left.get_max_entries();
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unsigned total = nr_left + nr_center + nr_right;
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unsigned target_right = total / 3;
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unsigned remainder = (target_right * 3) != total;
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unsigned target_left = target_right + remainder;
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if (target_left > max_entries || target_right > max_entries)
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throw std::runtime_error("too many entries");
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if (nr_left < nr_right) {
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int s = nr_left - target_left;
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// FIXME: signed & unsigned comparison
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if (s < 0 && nr_center < static_cast<unsigned>(-s)) {
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// not enough in central node
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left.move_entries(center, -nr_center);
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s += nr_center;
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left.move_entries(right, s);
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nr_right += s;
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} else
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left.move_entries(center, s);
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center.move_entries(right, target_right - nr_right);
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} else {
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int s = target_right - nr_right;
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if (s > 0 && nr_center < static_cast<unsigned>(s)) {
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// not enough in central node
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center.move_entries(right, nr_center);
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s -= nr_center;
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left.move_entries(right, s);
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nr_left -= s;
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} else
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center.move_entries(right, s);
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left.move_entries(center, nr_left - target_left);
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}
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parent.set_key(center_index, center.key_at(0));
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parent.set_key(right_index, right.key_at(0));
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}
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};
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