configuration_manager: using binary search to replace linear search. (#9

)

entries index of `configuration manager` is strictly increase
monotonically, we can use binary search to replace linear search.

details: #9

src/braft/configuration_manager.cpp

@@ -16,6 +16,8 @@
 
 #include "braft/configuration_manager.h"
 
+#include <algorithm>
+
 namespace braft {
 
 int ConfigurationManager::add(ConfigurationEntry&& entry) {
@@ -31,17 +33,27 @@ int ConfigurationManager::add(ConfigurationEntry&& entry) {
 }
 
 void ConfigurationManager::truncate_prefix(const int64_t first_index_kept) {
-    while (!_configurations.empty() &&
-           _configurations.front().id.index < first_index_kept) {
-        _configurations.pop_front();
-    }
+    // Find the first element which index >= `first_index_kept`.
+    auto it = std::lower_bound(
+        _configurations.begin(), _configurations.end(), first_index_kept,
+        [](const ConfigurationEntry& entry, int64_t index) {
+            return entry.id.index < index;
+        });
+
+    // Remove prefix [begin, index).
+    _configurations.erase(_configurations.begin(), it);
 }
 
 void ConfigurationManager::truncate_suffix(const int64_t last_index_kept) {
-    while (!_configurations.empty() &&
-           _configurations.back().id.index > last_index_kept) {
-        _configurations.pop_back();
-    }
+    // Find the first element which index > `last_index_kept`.
+    auto it = std::upper_bound(
+        _configurations.begin(), _configurations.end(), last_index_kept,
+        [](int64_t index, const ConfigurationEntry& entry) {
+            return index < entry.id.index;
+        });
+
+    // Remove suffix [index, end].
+    _configurations.erase(it, _configurations.end());
 }
 
 void ConfigurationManager::set_snapshot(ConfigurationEntry&& entry) {
@@ -56,17 +68,19 @@ void ConfigurationManager::get(int64_t last_included_index,
         *conf = _snapshot;
         return;
     }
-    std::deque<ConfigurationEntry>::iterator it;
-    for (it = _configurations.begin(); it != _configurations.end(); ++it) {
-        if (it->id.index > last_included_index) {
-            break;
-        }
-    }
-    if (it == _configurations.begin()) {
-        *conf = _snapshot;
-        return;
-    }
-    --it;
+
+    // Entries index is strictly increase monotonically.
+    // We can use binary search to find the i which
+    // _configurations[i-1].index < `last_included_index` <=
+    // _configurations[i].id.index
+    // From end to begin, the first element which index <= `last_included_index`
+    auto it = std::lower_bound(
+        _configurations.rbegin(), _configurations.rend(), last_included_index,
+        [](const ConfigurationEntry& rhs, int64_t index) {
+            return rhs.id.index > index;
+        });
+
+    CHECK(it != _configurations.rend());
     *conf = *it;
 }
 

test/test_configuration.cpp

@@ -114,20 +114,24 @@ TEST_F(TestUsageSuits, Configuration) {
     std::set<PeerId> peer_set3;
     conf2.list_peers(&peer_set3);
     ASSERT_EQ(peer_set.size(), 3);
-    
+
     // invalid format.
     Configuration conf4;
     ASSERT_EQ(conf4.parse_from("1.1,1.1:100,1.1.1:100:3,aaabbbccc"), -1);
 }
 
 TEST_F(TestUsageSuits, ConfigurationManager) {
     ConfigurationManager conf_manager;
-
     ConfigurationEntry it1;
     conf_manager.get(10, &it1);
     ASSERT_EQ(it1.id, LogId(0, 0));
     ASSERT_TRUE(it1.conf.empty());
+
+    // Truncate empty config manager.
+    conf_manager.truncate_prefix(42);
+    conf_manager.truncate_suffix(42);
     ASSERT_EQ(LogId(0, 0), conf_manager.last_configuration().id);
+
     ConfigurationEntry entry;
     std::vector<PeerId> peers;
     peers.emplace_back("1.1.1.1:1000:0");
@@ -138,26 +142,55 @@ TEST_F(TestUsageSuits, ConfigurationManager) {
     conf_manager.add(ConfigurationEntry{entry});
 
     ASSERT_EQ(LogId(8, 1), conf_manager.last_configuration().id);
-
+    conf_manager.get(8, &it1);
+    ASSERT_EQ(it1.id, entry.id);
     conf_manager.get(10, &it1);
     ASSERT_EQ(it1.id, entry.id);
 
+    // truncate suffix (8, end).
+    conf_manager.truncate_suffix(8);
+    // 8 must exists.
+    ASSERT_EQ(LogId(8, 1), conf_manager.last_configuration().id);
+
+    // truncate prefix [1, 8).
+    conf_manager.truncate_prefix(8);
+    // 8 must exists.
+    ASSERT_EQ(LogId(8, 1), conf_manager.last_configuration().id);
+
+    // truncate suffix (7, end).
     conf_manager.truncate_suffix(7);
+    // 8 not fount.
     ASSERT_EQ(LogId(0, 0), conf_manager.last_configuration().id);
 
+    // Add [10, 15, 20] entries.
     entry.id = LogId(10, 1);
     entry.conf = peers;
     conf_manager.add(ConfigurationEntry{entry});
     peers.emplace_back("1.1.1.1:1000:3");
+    entry.id = LogId(15, 1);
+    entry.conf = peers;
+    conf_manager.add(ConfigurationEntry{entry});
     entry.id = LogId(20, 1);
     entry.conf = peers;
     conf_manager.add(ConfigurationEntry{entry});
-    ASSERT_EQ(LogId(20, 1), conf_manager.last_configuration().id);
 
-    conf_manager.truncate_prefix(15);
     ASSERT_EQ(LogId(20, 1), conf_manager.last_configuration().id);
+    ConfigurationEntry ce;
+    conf_manager.get(16, &ce);
+    ASSERT_EQ(LogId(15, 1), ce.id);
+    // conf_manager.get(8, &ce); // FATAL.
+    // ASSERT_EQ(LogId(0, 0), ce.id);
 
-    conf_manager.truncate_prefix(25);
+    conf_manager.truncate_prefix(10);
+    conf_manager.get(10, &ce); 
+    ASSERT_EQ(LogId(10, 1), ce.id);
+
+    ASSERT_EQ(LogId(20, 1), conf_manager.last_configuration().id);
+    conf_manager.truncate_prefix(16);
+    ASSERT_EQ(LogId(20, 1), conf_manager.last_configuration().id);
+    conf_manager.truncate_suffix(20);
+    ASSERT_EQ(LogId(20, 1), conf_manager.last_configuration().id);
+    conf_manager.truncate_suffix(19);
     ASSERT_EQ(LogId(0, 0), conf_manager.last_configuration().id);
 }
 }  // namespace test