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Cache comparison between next elements in heap

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This commit is contained in:
Alexey Milovidov 2019-12-22 14:13:10 +03:00
parent 7ffa78ee95
commit bd7eed1204
2 changed files with 37 additions and 10 deletions
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44
dbms/src/Core/SortCursor.h
View File

@ -241,8 +241,20 @@ public:
size_t size() { return queue.size(); }
Cursor & firstChild() { return queue[1]; }
Cursor & secondChild() { return queue[2]; }
Cursor & nextChild()
{
if (next_idx)
{
return queue[next_idx];
}
else
{
next_idx = 1;
if (queue.size() > 2 && queue[1] < queue[2])
++next_idx;
return queue[next_idx];
}
}
void next()
{
@ -273,30 +285,46 @@ private:
using Container = std::vector<Cursor>;
Container queue;
/// Cache comparison between first and second child if the order in queue has not been changed.
size_t next_idx = 0;
/// This is adapted version of the function __sift_down from libc++.
/// Why cannot simply use std::priority_queue?
/// - because it doesn't support updating the top element and requires pop and push instead.
/// Also look at "Boost.Heap" library.
void updateTop()
{
size_t size = queue.size();
if (size < 2)
return;
size_t child_idx = 1;
auto begin = queue.begin();
auto child_it = begin + 1;
typename Container::iterator child_it;
/// Right child exists and is greater than left child.
if (size > 2 && *child_it < *(child_it + 1))
if (next_idx)
{
++child_it;
++child_idx;
child_it = begin + next_idx;
}
else
{
next_idx = 1;
child_it = begin + next_idx;
/// Right child exists and is greater than left child.
if (size > 2 && *child_it < *(child_it + 1))
{
++child_it;
++next_idx;
}
}
/// Check if we are in order.
if (*child_it < *begin)
return;
size_t child_idx = next_idx;
next_idx = 0;
auto curr_it = begin;
auto top(std::move(*begin));
do

3
dbms/src/DataStreams/MergingSortedBlockInputStream.cpp
View File

@ -187,8 +187,7 @@ void MergingSortedBlockInputStream::merge(MutableColumns & merged_columns, TSort
*/
if (current->isFirst()
&& (queue.size() == 1
|| (queue.size() == 2 && current.totallyLessOrEquals(queue.firstChild()))
|| (queue.size() >= 3 && current.totallyLessOrEquals(queue.firstChild()) && current.totallyLessOrEquals(queue.secondChild()))))
|| (queue.size() >= 2 && current.totallyLessOrEquals(queue.nextChild()))))
{
// std::cerr << "current block is totally less or equals\n";