[GitHub] [incubator-doris] morningman commented on a change in pull request #4803: [Feature] Add Topn udaf

[GitBox <gi...@apache.org>]

morningman commented on a change in pull request #4803:
URL: https://github.com/apache/incubator-doris/pull/4803#discussion_r528203668



##########
File path: gensrc/proto/olap_common.proto
##########
@@ -48,3 +48,14 @@ enum CompressKind {
     COMPRESS_LZ4 = 2;
 }
 
+message PCounter {
+    required string item = 1;
+    required uint64  count = 2;

Review comment:
       ```suggestion
       required uint64 count = 2;
   ```

##########
File path: be/src/util/topn_counter.cpp
##########
@@ -0,0 +1,138 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+#include <algorithm>
+#include "gen_cpp/olap_common.pb.h"
+#include "topn_counter.h"
+#include "slice.h"
+
+namespace doris {
+
+void TopNCounter::add_item(const std::string& item, uint64_t incrementCount) {
+    auto iter = _counter_map->find(item);
+    if (iter != _counter_map->end()) {
+        iter->second.add_count(incrementCount);
+    } else {
+        _counter_map->insert(std::make_pair(item, Counter(item, incrementCount)));
+    }
+    _ordered = false;
+}
+
+void TopNCounter::serialize(std::string* buffer) {
+    sort_retain(_capacity);
+    PTopNCounter topn_counter;
+    topn_counter.set_top_num(_top_num);
+    topn_counter.set_space_expand_rate(_space_expand_rate);
+    for(std::vector<Counter>::const_iterator it = _counter_vec->begin(); it != _counter_vec->end(); ++it)
+    {
+        PCounter* counter = topn_counter.add_counter();
+        counter->set_item(it->get_item());
+        counter->set_count(it->get_count());
+    }
+    topn_counter.SerializeToString(buffer);
+}
+
+bool TopNCounter::deserialize(const doris::Slice &src) {
+    PTopNCounter topn_counter;
+    if (!topn_counter.ParseFromArray(src.data, src.size)) {
+        LOG(WARNING) << "topn counter deserialize failed";
+        return false;
+    }
+
+    _space_expand_rate = topn_counter.space_expand_rate();
+    set_top_num(topn_counter.top_num());
+    for (int i = 0; i < topn_counter.counter_size(); ++i) {
+        const PCounter& counter = topn_counter.counter(i);
+        _counter_map->insert(std::make_pair(counter.item(), Counter(counter.item(), counter.count())));
+        _counter_vec->emplace_back(counter.item(), counter.count());
+    }
+    _ordered = true;
+    return true;
+}
+
+void TopNCounter::sort_retain(uint32_t capacity) {
+    _counter_vec->clear();
+    sort_retain(capacity, _counter_vec);
+    _ordered = true;
+}
+
+void TopNCounter::sort_retain(uint32_t capacity, std::vector<Counter>* sort_vec) {
+    for(std::unordered_map<std::string, Counter>::const_iterator it = _counter_map->begin(); it != _counter_map->end(); ++it) {
+        sort_vec->emplace_back(it->second.get_item(), it->second.get_count());
+    }
+
+    std::sort(sort_vec->begin(), sort_vec->end(), TopNComparator());
+    if (sort_vec->size() > capacity) {
+        for (uint32_t i = 0, n = sort_vec->size() - capacity; i < n; ++i) {
+            auto &counter = sort_vec->back();
+            _counter_map->erase(counter.get_item());
+            sort_vec->pop_back();
+        }
+    }
+}
+
+// Based on the  parallel version of the Space Saving algorithm as described in:
+// A parallel space saving algorithm for frequent items and the Hurwitz zeta distribution by Massimo Cafaro, et al.
+void TopNCounter::merge(doris::TopNCounter &&other) {
+    if (other._counter_map->size() == 0) {
+        return;
+    }
+
+    _space_expand_rate = other._space_expand_rate;
+    set_top_num(other._top_num);
+    bool this_full = _counter_map->size() >= _capacity;
+    bool another_full = other._counter_map->size() >= other._capacity;
+
+    uint64_t m1 = this_full ? _counter_vec->back().get_count() : 0;
+    uint64_t m2 = another_full ? other._counter_vec->back().get_count() : 0;
+   
+    if (another_full == true) {
+        for (auto &entry : *(this->_counter_map)) {
+            entry.second.add_count(m2);
+        }
+    }
+
+    for (auto &other_entry : *(other._counter_map)) {
+        auto itr = this->_counter_map->find(other_entry.first);
+        if (itr != _counter_map->end()) {
+            itr->second.add_count(other_entry.second.get_count() - m2);
+        } else {
+            this->_counter_map->insert(std::make_pair(other_entry.first,
+                    Counter(other_entry.first,other_entry.second.get_count() + m1)));
+        }
+    }
+    _ordered = false;
+    sort_retain(_capacity);
+}
+
+void TopNCounter::finalize(std::string& finalize_str) {

Review comment:
       How about using JSON format output?




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