VersionSet: optmize GetOverlappingInputsRangeBinarySearch (#4987)

Summary:
`GetOverlappingInputsRangeBinarySearch` firstly use binary search
to find a index in the given range `[begin, end]`. But after find
the index, then use linear search to find the `start_index` and
`end_index`. So the search process degraded to linear time.

Here optmize the search process with below changes:

- use `std::lower_bound` and `std::upper_bound` to get
  `lg(n)` search complexity.
- use uniformed lambda for search process.
- simplify process for `within_interval` true or false.
- remove function `ExtendFileRangeWithinInterval`
  and `ExtendFileRangeOverlappingInterval`.

Signed-off-by: JiYou <jiyou09@gmail.com>
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4987

Differential Revision: D14984192

Pulled By: riversand963

fbshipit-source-id: fae4b8e59a21b7e350718d60cdc94dd55ac81e89

db/version_set.cc

@@ -2772,14 +2772,6 @@ void VersionStorageInfo::GetCleanInputsWithinInterval(
     return;
   }
 
-  const auto& level_files = level_files_brief_[level];
-  if (begin == nullptr) {
-    begin = &level_files.files[0].file_metadata->smallest;
-  }
-  if (end == nullptr) {
-    end = &level_files.files[level_files.num_files - 1].file_metadata->largest;
-  }
-
   GetOverlappingInputsRangeBinarySearch(level, begin, end, inputs,
                                         hint_index, file_index,
                                         true /* within_interval */);
@@ -2797,67 +2789,94 @@ void VersionStorageInfo::GetOverlappingInputsRangeBinarySearch(
     std::vector<FileMetaData*>* inputs, int hint_index, int* file_index,
     bool within_interval, InternalKey** next_smallest) const {
   assert(level > 0);
-  int min = 0;
+
-  int mid = 0;
-  int max = static_cast<int>(files_[level].size()) - 1;
-  bool foundOverlap = false;
   auto user_cmp = user_comparator_;
+  const FdWithKeyRange* files = level_files_brief_[level].files;
+  const int num_files = static_cast<int>(level_files_brief_[level].num_files);
 
-  // if the caller already knows the index of a file that has overlap,
+  // begin to use binary search to find lower bound
-  // then we can skip the binary search.
+  // and upper bound.
-  if (hint_index != -1) {
+  int start_index = 0;
-    mid = hint_index;
+  int end_index = num_files;
-    foundOverlap = true;
-  }
 
-  while (!foundOverlap && min <= max) {
+  if (begin != nullptr) {
-    mid = (min + max)/2;
+    // if within_interval is true, with file_key would find
-    FdWithKeyRange* f = &(level_files_brief_[level].files[mid]);
+    // not overlapping ranges in std::lower_bound.
-    auto& smallest = f->file_metadata->smallest;
+    auto cmp = [&user_cmp, &within_interval](const FdWithKeyRange& f,
-    auto& largest = f->file_metadata->largest;
+                                             const InternalKey* k) {
-    if ((!within_interval && sstableKeyCompare(user_cmp, begin, largest) > 0) ||
+      auto& file_key = within_interval ? f.file_metadata->smallest
-        (within_interval && sstableKeyCompare(user_cmp, begin, smallest) > 0)) {
+                                       : f.file_metadata->largest;
-      min = mid + 1;
+      return sstableKeyCompare(user_cmp, file_key, *k) < 0;
-    } else if ((!within_interval &&
+    };
-                sstableKeyCompare(user_cmp, smallest, end) > 0) ||
+
-               (within_interval &&
+    start_index = static_cast<int>(
-                sstableKeyCompare(user_cmp, largest, end) > 0)) {
+        std::lower_bound(files,
-      max = mid - 1;
+                         files + (hint_index == -1 ? num_files : hint_index),
-    } else {
+                         begin, cmp) -
-      foundOverlap = true;
+        files);
-      break;
+
+    if (start_index > 0 && within_interval) {
+      bool is_overlapping = true;
+      while (is_overlapping && start_index < num_files) {
+        auto& pre_limit = files[start_index - 1].file_metadata->largest;
+        auto& cur_start = files[start_index].file_metadata->smallest;
+        is_overlapping = sstableKeyCompare(user_cmp, pre_limit, cur_start) == 0;
+        start_index += is_overlapping;
+      }
     }
   }
 
+  if (end != nullptr) {
+    // if within_interval is true, with file_key would find
+    // not overlapping ranges in std::upper_bound.
+    auto cmp = [&user_cmp, &within_interval](const InternalKey* k,
+                                             const FdWithKeyRange& f) {
+      auto& file_key = within_interval ? f.file_metadata->largest
+                                       : f.file_metadata->smallest;
+      return sstableKeyCompare(user_cmp, *k, file_key) < 0;
+    };
+
+    end_index = static_cast<int>(
+        std::upper_bound(files + start_index, files + num_files, end, cmp) -
+        files);
+
+    if (end_index < num_files && within_interval) {
+      bool is_overlapping = true;
+      while (is_overlapping && end_index > start_index) {
+        auto& next_start = files[end_index].file_metadata->smallest;
+        auto& cur_limit = files[end_index - 1].file_metadata->largest;
+        is_overlapping =
+            sstableKeyCompare(user_cmp, cur_limit, next_start) == 0;
+        end_index -= is_overlapping;
+      }
+    }
+  }
+
+  assert(start_index <= end_index);
+
   // If there were no overlapping files, return immediately.
-  if (!foundOverlap) {
+  if (start_index == end_index) {
     if (next_smallest) {
       next_smallest = nullptr;
     }
     return;
   }
+
+  assert(start_index < end_index);
+
   // returns the index where an overlap is found
   if (file_index) {
-    *file_index = mid;
+    *file_index = start_index;
   }
 
-  int start_index, end_index;
-  if (within_interval) {
-    ExtendFileRangeWithinInterval(level, begin, end, mid,
-                                  &start_index, &end_index);
-  } else {
-    ExtendFileRangeOverlappingInterval(level, begin, end, mid,
-                                       &start_index, &end_index);
-    assert(end_index >= start_index);
-  }
   // insert overlapping files into vector
-  for (int i = start_index; i <= end_index; i++) {
+  for (int i = start_index; i < end_index; i++) {
     inputs->push_back(files_[level][i]);
   }
 
   if (next_smallest != nullptr) {
     // Provide the next key outside the range covered by inputs
-    if (++end_index < static_cast<int>(files_[level].size())) {
+    if (end_index < static_cast<int>(files_[level].size())) {
       **next_smallest = files_[level][end_index]->smallest;
     } else {
       *next_smallest = nullptr;
@@ -2865,136 +2884,6 @@ void VersionStorageInfo::GetOverlappingInputsRangeBinarySearch(
   }
 }
 
-// Store in *start_index and *end_index the range of all files in
-// "level" that overlap [begin,end]
-// The mid_index specifies the index of at least one file that
-// overlaps the specified range. From that file, iterate backward
-// and forward to find all overlapping files.
-// Use FileLevel in searching, make it faster
-void VersionStorageInfo::ExtendFileRangeOverlappingInterval(
-    int level, const InternalKey* begin, const InternalKey* end,
-    unsigned int mid_index, int* start_index, int* end_index) const {
-  auto user_cmp = user_comparator_;
-  const FdWithKeyRange* files = level_files_brief_[level].files;
-#ifndef NDEBUG
-  {
-    // assert that the file at mid_index overlaps with the range
-    assert(mid_index < level_files_brief_[level].num_files);
-    const FdWithKeyRange* f = &files[mid_index];
-    auto& smallest = f->file_metadata->smallest;
-    auto& largest = f->file_metadata->largest;
-    if (sstableKeyCompare(user_cmp, begin, smallest) <= 0) {
-      assert(sstableKeyCompare(user_cmp, smallest, end) <= 0);
-    } else {
-      // fprintf(stderr, "ExtendFileRangeOverlappingInterval\n%s - %s\n%s - %s\n%d %d\n",
-      //         begin ? begin->DebugString().c_str() : "(null)",
-      //         end ? end->DebugString().c_str() : "(null)",
-      //         smallest->DebugString().c_str(),
-      //         largest->DebugString().c_str(),
-      //         sstableKeyCompare(user_cmp, smallest, begin),
-      //         sstableKeyCompare(user_cmp, largest, begin));
-      assert(sstableKeyCompare(user_cmp, begin, largest) <= 0);
-    }
-  }
-#endif
-  *start_index = mid_index + 1;
-  *end_index = mid_index;
-  int count __attribute__((__unused__));
-  count = 0;
-
-  // check backwards from 'mid' to lower indices
-  for (int i = mid_index; i >= 0 ; i--) {
-    const FdWithKeyRange* f = &files[i];
-    auto& largest = f->file_metadata->largest;
-    if (sstableKeyCompare(user_cmp, begin, largest) <= 0) {
-      *start_index = i;
-      assert((count++, true));
-    } else {
-      break;
-    }
-  }
-  // check forward from 'mid+1' to higher indices
-  for (unsigned int i = mid_index+1;
-       i < level_files_brief_[level].num_files; i++) {
-    const FdWithKeyRange* f = &files[i];
-    auto& smallest = f->file_metadata->smallest;
-    if (sstableKeyCompare(user_cmp, smallest, end) <= 0) {
-      assert((count++, true));
-      *end_index = i;
-    } else {
-      break;
-    }
-  }
-  assert(count == *end_index - *start_index + 1);
-}
-
-// Store in *start_index and *end_index the clean range of all files in
-// "level" within [begin,end]
-// The mid_index specifies the index of at least one file within
-// the specified range. From that file, iterate backward
-// and forward to find all overlapping files and then "shrink" to
-// the clean range required.
-// Use FileLevel in searching, make it faster
-void VersionStorageInfo::ExtendFileRangeWithinInterval(
-    int level, const InternalKey* begin, const InternalKey* end,
-    unsigned int mid_index, int* start_index, int* end_index) const {
-  assert(level != 0);
-  auto* user_cmp = user_comparator_;
-  const FdWithKeyRange* files = level_files_brief_[level].files;
-#ifndef NDEBUG
-  {
-    // assert that the file at mid_index is within the range
-    assert(mid_index < level_files_brief_[level].num_files);
-    const FdWithKeyRange* f = &files[mid_index];
-    auto& smallest = f->file_metadata->smallest;
-    auto& largest = f->file_metadata->largest;
-    assert(sstableKeyCompare(user_cmp, begin, smallest) <= 0 &&
-           sstableKeyCompare(user_cmp, largest, end) <= 0);
-  }
-#endif
-  ExtendFileRangeOverlappingInterval(level, begin, end, mid_index,
-                                     start_index, end_index);
-  int left = *start_index;
-  int right = *end_index;
-  // shrink from left to right
-  while (left <= right) {
-    auto& smallest = files[left].file_metadata->smallest;
-    if (sstableKeyCompare(user_cmp, begin, smallest) > 0) {
-      left++;
-      continue;
-    }
-    if (left > 0) {  // If not first file
-      auto& largest = files[left - 1].file_metadata->largest;
-      if (sstableKeyCompare(user_cmp, smallest, largest) == 0) {
-        left++;
-        continue;
-      }
-    }
-    break;
-  }
-  // shrink from right to left
-  while (left <= right) {
-    auto& largest = files[right].file_metadata->largest;
-    if (sstableKeyCompare(user_cmp, largest, end) > 0) {
-      right--;
-      continue;
-    }
-    if (right < static_cast<int>(level_files_brief_[level].num_files) -
-                    1) {  // If not the last file
-      auto& smallest = files[right + 1].file_metadata->smallest;
-      if (sstableKeyCompare(user_cmp, smallest, largest) == 0) {
-        // The last user key in range overlaps with the next file's first key
-        right--;
-        continue;
-      }
-    }
-    break;
-  }
-
-  *start_index = left;
-  *end_index = right;
-}
-
 uint64_t VersionStorageInfo::NumLevelBytes(int level) const {
   assert(level >= 0);
   assert(level < num_levels());

db/version_set.h

@@ -220,24 +220,6 @@ class VersionStorageInfo {
       InternalKey** next_smallest = nullptr)  // if non-null, returns the
       const;  // smallest key of next file not included
 
-  void ExtendFileRangeOverlappingInterval(
-      int level,
-      const InternalKey* begin,  // nullptr means before all keys
-      const InternalKey* end,    // nullptr means after all keys
-      unsigned int index,        // start extending from this index
-      int* startIndex,           // return the startIndex of input range
-      int* endIndex)             // return the endIndex of input range
-      const;
-
-  void ExtendFileRangeWithinInterval(
-      int level,
-      const InternalKey* begin,  // nullptr means before all keys
-      const InternalKey* end,    // nullptr means after all keys
-      unsigned int index,        // start extending from this index
-      int* startIndex,           // return the startIndex of input range
-      int* endIndex)             // return the endIndex of input range
-      const;
-
   // Returns true iff some file in the specified level overlaps
   // some part of [*smallest_user_key,*largest_user_key].
   // smallest_user_key==NULL represents a key smaller than all keys in the DB.