From 87567c3c2a55c156175d77113bdb2e9de3225600 Mon Sep 17 00:00:00 2001
From: Jan <jsteemann@users.noreply.github.com>
Date: Sun, 30 Jul 2017 14:24:25 +0200
Subject: [PATCH] fixed issue #2876 (#2896)

---
 CHANGELOG                                   |  2 ++
 arangod/MMFiles/MMFilesSkiplistIndex.cpp    | 26 +++++++++++++++------
 arangod/RocksDBEngine/RocksDBVPackIndex.cpp | 26 +++++++++++++++++++--
 3 files changed, 45 insertions(+), 9 deletions(-)

diff --git a/CHANGELOG b/CHANGELOG
index 53ff78c999..6aaadb462c 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,6 +1,8 @@
 devel
 -----
 
+* fixed issue #2876: wrong skiplist index usage in edge collection
+
 * fixed issue #2868: cname missing from logger-follow results in rocksdb
 
 * fixed issue #2889: Traversal query using incorrect collection id
diff --git a/arangod/MMFiles/MMFilesSkiplistIndex.cpp b/arangod/MMFiles/MMFilesSkiplistIndex.cpp
index 84dfcc2abd..a221b033d3 100644
--- a/arangod/MMFiles/MMFilesSkiplistIndex.cpp
+++ b/arangod/MMFiles/MMFilesSkiplistIndex.cpp
@@ -1281,6 +1281,7 @@ bool MMFilesSkiplistIndex::supportsFilterCondition(
     arangodb::aql::AstNode const* node,
     arangodb::aql::Variable const* reference, size_t itemsInIndex,
     size_t& estimatedItems, double& estimatedCost) const {
+
   std::unordered_map<size_t, std::vector<arangodb::aql::AstNode const*>> found;
   std::unordered_set<std::string> nonNullAttributes;
   size_t values = 0;
@@ -1349,12 +1350,19 @@ bool MMFilesSkiplistIndex::supportsFilterCondition(
   if (attributesCoveredByEquality == _fields.size() &&
       (unique() || implicitlyUnique())) {
     // index is unique and condition covers all attributes by equality
-    if (estimatedItems >= values) {
-      // reduce costs due to uniqueness
-      estimatedItems = values;
-      estimatedCost = static_cast<double>(estimatedItems);
+    if (itemsInIndex == 0) {
+      estimatedItems = 0;
+      estimatedCost = 0.0;
+      return true;
     }
-    // cost is already low... now slightly prioritize the unique index
+
+    if (estimatedItems >= values) {
+      TRI_ASSERT(itemsInIndex > 0);
+
+      estimatedItems = values;
+      estimatedCost = (std::max)(static_cast<double>(1), std::log2(static_cast<double>(itemsInIndex)) * values);
+    }
+    // cost is already low... now slightly prioritize unique indexes
     estimatedCost *= 0.995 - 0.05 * (_fields.size() - 1);
     return true;
   }
@@ -1367,11 +1375,15 @@ bool MMFilesSkiplistIndex::supportsFilterCondition(
     // sparse indexes are contained in Index::canUseConditionPart)
     estimatedItems = static_cast<size_t>((std::max)(
         static_cast<size_t>(estimatedCost * values), static_cast<size_t>(1)));
-    estimatedCost *= static_cast<double>(values);
+    if (itemsInIndex == 0) {
+      estimatedCost = 0.0;
+    } else {
+      estimatedCost = (std::max)(static_cast<double>(1), std::log2(static_cast<double>(itemsInIndex)) * values);
+    }
     return true;
   }
 
-  // no condition
+  // index does not help for this condition
   estimatedItems = itemsInIndex;
   estimatedCost = static_cast<double>(estimatedItems);
   return false;
diff --git a/arangod/RocksDBEngine/RocksDBVPackIndex.cpp b/arangod/RocksDBEngine/RocksDBVPackIndex.cpp
index 078b4fecd8..9827eca572 100644
--- a/arangod/RocksDBEngine/RocksDBVPackIndex.cpp
+++ b/arangod/RocksDBEngine/RocksDBVPackIndex.cpp
@@ -977,8 +977,22 @@ bool RocksDBVPackIndex::supportsFilterCondition(
 
   if (attributesCoveredByEquality == _fields.size() && unique()) {
     // index is unique and condition covers all attributes by equality
+    if (itemsInIndex == 0) {
+      estimatedItems = 0;
+      estimatedCost = 0.0;
+      return true;
+    }
     estimatedItems = values;
     estimatedCost = 0.995 * values;
+    if (values > 0) {
+      if (useCache()) {
+        estimatedCost = static_cast<double>(estimatedItems  * values);
+      } else {
+        estimatedCost = (std::max)(static_cast<double>(1), std::log2(static_cast<double>(itemsInIndex)) * values);
+      }
+    }
+    // cost is already low... now slightly prioritize unique indexes
+    estimatedCost *= 0.995 - 0.05 * (_fields.size() - 1);
     return true;
   }
 
@@ -1000,11 +1014,19 @@ bool RocksDBVPackIndex::supportsFilterCondition(
         estimatedItems = static_cast<size_t>(1.0 / estimate);
       }
     }
-    estimatedCost = static_cast<double>(estimatedItems);
+    if (itemsInIndex == 0) {
+      estimatedCost = 0.0;
+    } else {
+      if (useCache()) {
+        estimatedCost = static_cast<double>(estimatedItems * values);
+      } else {
+        estimatedCost = (std::max)(static_cast<double>(1), std::log2(static_cast<double>(itemsInIndex)) * values);
+      }
+    }
     return true;
   }
 
-  // no condition
+  // index does not help for this condition
   estimatedItems = itemsInIndex;
   estimatedCost = static_cast<double>(estimatedItems);
   return false;