Merge branch 'performance' of github.com:facebook/rocksdb into performance

Conflicts:
	db/builder.cc
	db/db_impl.cc
	db/version_set.cc
	include/leveldb/statistics.h

db/builder.cc

@@ -28,6 +28,7 @@ Status BuildTable(const std::string& dbname,
                   const SequenceNumber earliest_seqno_in_memtable) {
   Status s;
   meta->file_size = 0;
+  meta->smallest_seqno = meta->largest_seqno = 0;
   iter->SeekToFirst();
 
   // If the sequence number of the smallest entry in the memtable is
@@ -48,7 +49,10 @@ Status BuildTable(const std::string& dbname,
     TableBuilder* builder = new TableBuilder(options, file.get(), 0);
 
     // the first key is the smallest key
-    meta->smallest.DecodeFrom(iter->key());
+    Slice key = iter->key();
+    meta->smallest.DecodeFrom(key);
+    meta->smallest_seqno = GetInternalKeySeqno(key);
+    meta->largest_seqno = meta->smallest_seqno;
 
     MergeHelper merge(user_comparator, options.merge_operator,
                       options.info_log.get(),
@@ -135,12 +139,18 @@ Status BuildTable(const std::string& dbname,
 
       // The last key is the largest key
       meta->largest.DecodeFrom(Slice(prev_key));
+      SequenceNumber seqno = GetInternalKeySeqno(Slice(prev_key));
+      meta->smallest_seqno = std::min(meta->smallest_seqno, seqno);
+      meta->largest_seqno = std::max(meta->largest_seqno, seqno);
 
     } else {
       for (; iter->Valid(); iter->Next()) {
         Slice key = iter->key();
         meta->largest.DecodeFrom(key);
         builder->Add(key, iter->value());
+        SequenceNumber seqno = GetInternalKeySeqno(key);
+        meta->smallest_seqno = std::min(meta->smallest_seqno, seqno);
+        meta->largest_seqno = std::max(meta->largest_seqno, seqno);
       }
     }
 

db/db_bench.cc

@@ -9,6 +9,7 @@
 #include "db/db_impl.h"
 #include "db/version_set.h"
 #include "db/db_statistics.h"
+#include "leveldb/options.h"
 #include "leveldb/cache.h"
 #include "leveldb/db.h"
 #include "leveldb/env.h"
@@ -125,7 +126,7 @@ static int FLAGS_max_write_buffer_number = 0;
 // The minimum number of write buffers that will be merged together
 // before writing to storage. This is cheap because it is an
 // in-memory merge. If this feature is not enabled, then all these
-// write buffers are fushed to L0 as seperate files and this increases
+// write buffers are fushed to L0 as separate files and this increases
 // read amplification because a get request has to check in all of these
 // files. Also, an in-memory merge may result in writing lesser
 // data to storage if there are duplicate records in each of these
@@ -137,6 +138,15 @@ static int FLAGS_min_write_buffer_number_to_merge = 0;
 // This is initialized to default value of 1 in "main" function.
 static int FLAGS_max_background_compactions = 0;
 
+// style of compaction: level-based vs universal
+static leveldb::CompactionStyle FLAGS_compaction_style = leveldb::kCompactionStyleLevel;
+
+// Percentage flexibilty while comparing file size.
+static int FLAGS_universal_size_ratio = 1;
+
+// The minimum number of files in a single compaction run.
+static int FLAGS_compaction_universal_min_merge_width = 2;
+
 // Number of bytes to use as a cache of uncompressed data.
 // Negative means use default settings.
 static long FLAGS_cache_size = -1;
@@ -1104,6 +1114,10 @@ unique_ptr<char []> GenerateKeyFromInt(int v, const char* suffix = "")
     options.min_write_buffer_number_to_merge =
       FLAGS_min_write_buffer_number_to_merge;
     options.max_background_compactions = FLAGS_max_background_compactions;
+    options.compaction_style = FLAGS_compaction_style;
+    options.compaction_options_universal.size_ratio = FLAGS_universal_size_ratio;
+    options.compaction_options_universal.min_merge_width =
+      FLAGS_compaction_universal_min_merge_width;
     options.block_size = FLAGS_block_size;
     options.filter_policy = filter_policy_;
     options.max_open_files = FLAGS_open_files;
@@ -1988,6 +2002,11 @@ int main(int argc, char** argv) {
   FLAGS_open_files = leveldb::Options().max_open_files;
   FLAGS_max_background_compactions =
     leveldb::Options().max_background_compactions;
+  FLAGS_compaction_style = leveldb::Options().compaction_style;
+  FLAGS_universal_size_ratio =
+    leveldb::Options().compaction_options_universal.size_ratio;
+  FLAGS_compaction_universal_min_merge_width =
+    leveldb::Options().compaction_options_universal.min_merge_width;
   // Compression test code above refers to FLAGS_block_size
   FLAGS_block_size = leveldb::Options().block_size;
   FLAGS_use_os_buffer = leveldb::EnvOptions().use_os_buffer;
@@ -2047,6 +2066,13 @@ int main(int argc, char** argv) {
     } else if (sscanf(argv[i], "--max_background_compactions=%d%c", &n, &junk)
                == 1) {
       FLAGS_max_background_compactions = n;
+    } else if (sscanf(argv[i], "--compaction_style=%d%c", &n, &junk) == 1) {
+      FLAGS_compaction_style = (leveldb::CompactionStyle)n;
+    } else if (sscanf(argv[i], "--universal_size_ratio=%d%c", &n, &junk) == 1) {
+      FLAGS_universal_size_ratio = n;
+    } else if (sscanf(argv[i], "--universal_min_merge_width=%d%c",
+               &n, &junk) == 1) {
+      FLAGS_compaction_universal_min_merge_width = n;
     } else if (sscanf(argv[i], "--cache_size=%ld%c", &l, &junk) == 1) {
       FLAGS_cache_size = l;
     } else if (sscanf(argv[i], "--block_size=%d%c", &n, &junk) == 1) {

db/db_impl.cc

@@ -76,6 +76,7 @@ struct DBImpl::CompactionState {
     uint64_t number;
     uint64_t file_size;
     InternalKey smallest, largest;
+    SequenceNumber smallest_seqno, largest_seqno;
   };
   std::vector<Output> outputs;
   std::list<uint64_t> allocated_file_numbers;
@@ -780,7 +781,8 @@ Status DBImpl::WriteLevel0TableForRecovery(MemTable* mem, VersionEdit* edit) {
   int level = 0;
   if (s.ok() && meta.file_size > 0) {
     edit->AddFile(level, meta.number, meta.file_size,
-                  meta.smallest, meta.largest);
+                  meta.smallest, meta.largest,
+                  meta.smallest_seqno, meta.largest_seqno);
   }
 
   CompactionStats stats;
@@ -854,11 +856,13 @@ Status DBImpl::WriteLevel0Table(std::vector<MemTable*> &mems, VersionEdit* edit,
     // insert files directly into higher levels because some other
     // threads could be concurrently producing compacted files for
     // that key range.
-    if (base != nullptr && options_.max_background_compactions <= 1) {
+    if (base != nullptr && options_.max_background_compactions <= 1 &&
+        options_.compaction_style == kCompactionStyleLevel) {
       level = base->PickLevelForMemTableOutput(min_user_key, max_user_key);
     }
     edit->AddFile(level, meta.number, meta.file_size,
-                  meta.smallest, meta.largest);
+                  meta.smallest, meta.largest,
+                  meta.smallest_seqno, meta.largest_seqno);
   }
 
   CompactionStats stats;
@@ -991,7 +995,8 @@ void DBImpl::ReFitLevel(int level) {
     VersionEdit edit(NumberLevels());
     for (const auto& f : versions_->current()->files_[level]) {
       edit.DeleteFile(level, f->number);
-      edit.AddFile(to_level, f->number, f->file_size, f->smallest, f->largest);
+      edit.AddFile(to_level, f->number, f->file_size, f->smallest, f->largest,
+                   f->smallest_seqno, f->largest_seqno);
     }
     Log(options_.info_log, "Apply version edit:\n%s",
         edit.DebugString().data());
@@ -1452,7 +1457,8 @@ Status DBImpl::BackgroundCompaction(bool* madeProgress,
     FileMetaData* f = c->input(0, 0);
     c->edit()->DeleteFile(c->level(), f->number);
     c->edit()->AddFile(c->level() + 1, f->number, f->file_size,
-                       f->smallest, f->largest);
+                       f->smallest, f->largest,
+                       f->smallest_seqno, f->largest_seqno);
     status = versions_->LogAndApply(c->edit(), &mutex_);
     VersionSet::LevelSummaryStorage tmp;
     Log(options_.info_log, "Moved #%lld to level-%d %lld bytes %s: %s\n",
@@ -1564,6 +1570,7 @@ Status DBImpl::OpenCompactionOutputFile(CompactionState* compact) {
   out.number = file_number;
   out.smallest.Clear();
   out.largest.Clear();
+  out.smallest_seqno = out.largest_seqno = 0;
   compact->outputs.push_back(out);
 
   // Make the output file
@@ -1574,10 +1581,10 @@ Status DBImpl::OpenCompactionOutputFile(CompactionState* compact) {
     // Over-estimate slightly so we don't end up just barely crossing
     // the threshold.
     compact->outfile->SetPreallocationBlockSize(
-      1.1 * versions_->MaxFileSizeForLevel(compact->compaction->level() + 1));
+      1.1 * versions_->MaxFileSizeForLevel(compact->compaction->output_level()));
 
     compact->builder.reset(new TableBuilder(options_, compact->outfile.get(),
-                                            compact->compaction->level() + 1));
+                                            compact->compaction->output_level()));
   }
   return s;
 }
@@ -1668,8 +1675,10 @@ Status DBImpl::InstallCompactionResults(CompactionState* compact) {
   for (size_t i = 0; i < compact->outputs.size(); i++) {
     const CompactionState::Output& out = compact->outputs[i];
     compact->compaction->edit()->AddFile(
-        level + 1,
+        (options_.compaction_style == kCompactionStyleUniversal) ?
-        out.number, out.file_size, out.smallest, out.largest);
+          level : level + 1,
+        out.number, out.file_size, out.smallest, out.largest,
+        out.smallest_seqno, out.largest_seqno);
   }
   return versions_->LogAndApply(compact->compaction->edit(), &mutex_);
 }
@@ -1950,7 +1959,8 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
         // If this is the bottommost level (no files in lower levels)
         // and the earliest snapshot is larger than this seqno
         // then we can squash the seqno to zero.
-        if (bottommost_level && ikey.sequence < earliest_snapshot &&
+        if (options_.compaction_style == kCompactionStyleLevel &&
+            bottommost_level && ikey.sequence < earliest_snapshot &&
             ikey.type != kTypeMerge) {
           assert(ikey.type != kTypeDeletion);
           // make a copy because updating in place would cause problems
@@ -1970,11 +1980,19 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
             break;
           }
         }
+
+        SequenceNumber seqno = GetInternalKeySeqno(newkey);
         if (compact->builder->NumEntries() == 0) {
           compact->current_output()->smallest.DecodeFrom(newkey);
+          compact->current_output()->smallest_seqno = seqno;
+        } else {
+          compact->current_output()->smallest_seqno =
+            std::min(compact->current_output()->smallest_seqno, seqno);
         }
         compact->current_output()->largest.DecodeFrom(newkey);
         compact->builder->Add(newkey, value);
+        compact->current_output()->largest_seqno =
+          std::max(compact->current_output()->largest_seqno, seqno);
 
         // Close output file if it is big enough
         if (compact->builder->FileSize() >=

db/db_test.cc

@@ -3401,7 +3401,7 @@ void BM_LogAndApply(int iters, int num_base_files) {
   for (int i = 0; i < num_base_files; i++) {
     InternalKey start(MakeKey(2*fnum), 1, kTypeValue);
     InternalKey limit(MakeKey(2*fnum+1), 1, kTypeDeletion);
-    vbase.AddFile(2, fnum++, 1 /* file size */, start, limit);
+    vbase.AddFile(2, fnum++, 1 /* file size */, start, limit, 1, 1);
   }
   ASSERT_OK(vset.LogAndApply(&vbase, &mu));
 
@@ -3412,7 +3412,7 @@ void BM_LogAndApply(int iters, int num_base_files) {
     vedit.DeleteFile(2, fnum);
     InternalKey start(MakeKey(2*fnum), 1, kTypeValue);
     InternalKey limit(MakeKey(2*fnum+1), 1, kTypeDeletion);
-    vedit.AddFile(2, fnum++, 1 /* file size */, start, limit);
+    vedit.AddFile(2, fnum++, 1 /* file size */, start, limit, 1, 1);
     vset.LogAndApply(&vedit, &mu);
   }
   uint64_t stop_micros = env->NowMicros();

db/dbformat.h

@@ -173,6 +173,15 @@ inline void UpdateInternalKey(char* internal_key,
   EncodeFixed64(seqtype, newval);
 }
 
+// Get the sequence number from the internal key
+inline uint64_t GetInternalKeySeqno(const Slice& internal_key) {
+  const size_t n = internal_key.size();
+  assert(n >= 8);
+  uint64_t num = DecodeFixed64(internal_key.data() + n - 8);
+  return num >> 8;
+}
+
+
 // A helper class useful for DBImpl::Get()
 class LookupKey {
  public:

db/repair.cc

@@ -88,6 +88,7 @@ class Repairer {
  private:
   struct TableInfo {
     FileMetaData meta;
+    SequenceNumber min_sequence;
     SequenceNumber max_sequence;
   };
 
@@ -264,6 +265,7 @@ class Repairer {
           ReadOptions(), storage_options_, t->meta.number, t->meta.file_size);
       bool empty = true;
       ParsedInternalKey parsed;
+      t->min_sequence = 0;
       t->max_sequence = 0;
       for (iter->SeekToFirst(); iter->Valid(); iter->Next()) {
         Slice key = iter->key();
@@ -280,6 +282,9 @@ class Repairer {
           t->meta.smallest.DecodeFrom(key);
         }
         t->meta.largest.DecodeFrom(key);
+        if (parsed.sequence < t->min_sequence) {
+          t->min_sequence = parsed.sequence;
+        }
         if (parsed.sequence > t->max_sequence) {
           t->max_sequence = parsed.sequence;
         }
@@ -320,7 +325,8 @@ class Repairer {
       // TODO(opt): separate out into multiple levels
       const TableInfo& t = tables_[i];
       edit_->AddFile(0, t.meta.number, t.meta.file_size,
-                    t.meta.smallest, t.meta.largest);
+                    t.meta.smallest, t.meta.largest,
+                    t.min_sequence, t.max_sequence);
     }
 
     //fprintf(stderr, "NewDescriptor:\n%s\n", edit_.DebugString().c_str());

db/version_edit.cc

@@ -20,7 +20,10 @@ enum Tag {
   kDeletedFile          = 6,
   kNewFile              = 7,
   // 8 was used for large value refs
-  kPrevLogNumber        = 9
+  kPrevLogNumber        = 9,
+
+  // these are new formats divergent from open source leveldb
+  kNewFile2             = 100  // store smallest & largest seqno
 };
 
 void VersionEdit::Clear() {
@@ -76,12 +79,14 @@ void VersionEdit::EncodeTo(std::string* dst) const {
 
   for (size_t i = 0; i < new_files_.size(); i++) {
     const FileMetaData& f = new_files_[i].second;
-    PutVarint32(dst, kNewFile);
+    PutVarint32(dst, kNewFile2);
     PutVarint32(dst, new_files_[i].first);  // level
     PutVarint64(dst, f.number);
     PutVarint64(dst, f.file_size);
     PutLengthPrefixedSlice(dst, f.smallest.Encode());
     PutLengthPrefixedSlice(dst, f.largest.Encode());
+    PutVarint64(dst, f.smallest_seqno);
+    PutVarint64(dst, f.largest_seqno);
   }
 }
 
@@ -201,6 +206,22 @@ Status VersionEdit::DecodeFrom(const Slice& src) {
         }
         break;
 
+      case kNewFile2:
+        if (GetLevel(&input, &level, &msg) &&
+            GetVarint64(&input, &f.number) &&
+            GetVarint64(&input, &f.file_size) &&
+            GetInternalKey(&input, &f.smallest) &&
+            GetInternalKey(&input, &f.largest) &&
+            GetVarint64(&input, &f.smallest_seqno) &&
+            GetVarint64(&input, &f.largest_seqno) ) {
+          new_files_.push_back(std::make_pair(level, f));
+        } else {
+          if (!msg) {
+            msg = "new-file2 entry";
+          }
+        }
+        break;
+
       default:
         msg = "unknown tag";
         break;

db/version_edit.h

@@ -22,6 +22,8 @@ struct FileMetaData {
   InternalKey smallest;       // Smallest internal key served by table
   InternalKey largest;        // Largest internal key served by table
   bool being_compacted;       // Is this file undergoing compaction?
+  SequenceNumber smallest_seqno;// The smallest seqno in this file
+  SequenceNumber largest_seqno; // The largest seqno in this file
 
   FileMetaData() : refs(0), allowed_seeks(1 << 30), file_size(0),
                    being_compacted(false) { }
@@ -67,12 +69,17 @@ class VersionEdit {
   void AddFile(int level, uint64_t file,
                uint64_t file_size,
                const InternalKey& smallest,
-               const InternalKey& largest) {
+               const InternalKey& largest,
+               const SequenceNumber& smallest_seqno,
+               const SequenceNumber& largest_seqno) {
     FileMetaData f;
     f.number = file;
     f.file_size = file_size;
     f.smallest = smallest;
     f.largest = largest;
+    f.smallest_seqno = smallest_seqno;
+    f.largest_seqno = largest_seqno;
+    assert(smallest_seqno <= largest_seqno);
     new_files_.push_back(std::make_pair(level, f));
   }
 

db/version_edit_test.cc

@@ -27,7 +27,9 @@ TEST(VersionEditTest, EncodeDecode) {
     TestEncodeDecode(edit);
     edit.AddFile(3, kBig + 300 + i, kBig + 400 + i,
                  InternalKey("foo", kBig + 500 + i, kTypeValue),
-                 InternalKey("zoo", kBig + 600 + i, kTypeDeletion));
+                 InternalKey("zoo", kBig + 600 + i, kTypeDeletion),
+                 kBig + 500 + i,
+                 kBig + 600 + i);
     edit.DeleteFile(4, kBig + 700 + i);
     edit.SetCompactPointer(i, InternalKey("x", kBig + 900 + i, kTypeValue));
   }

db/version_set.cc

@@ -5,6 +5,7 @@
 #include "db/version_set.h"
 
 #include <algorithm>
+#include <climits>
 #include <stdio.h>
 #include "db/filename.h"
 #include "db/log_reader.h"
@@ -22,8 +23,8 @@
 
 namespace leveldb {
 
-static int64_t TotalFileSize(const std::vector<FileMetaData*>& files) {
+static uint64_t TotalFileSize(const std::vector<FileMetaData*>& files) {
-  int64_t sum = 0;
+  uint64_t sum = 0;
   for (size_t i = 0; i < files.size() && files[i]; i++) {
     sum += files[i]->file_size;
   }
@@ -338,6 +339,14 @@ static bool SaveValue(void* arg, const Slice& ikey, const Slice& v, bool didIO){
 static bool NewestFirst(FileMetaData* a, FileMetaData* b) {
   return a->number > b->number;
 }
+static bool NewestFirstBySeqNo(FileMetaData* a, FileMetaData* b) {
+  if (a->smallest_seqno > b->smallest_seqno) {
+    assert(a->largest_seqno > b->largest_seqno);
+    return true;
+  }
+  assert(a->largest_seqno <= b->largest_seqno);
+  return false;
+}
 
 Version::Version(VersionSet* vset, uint64_t version_number)
     : vset_(vset), next_(this), prev_(this), refs_(0),
@@ -434,7 +443,11 @@ void Version::Get(const ReadOptions& options,
     if (important_files.empty()) continue;
 
     if (level == 0) {
+      if (vset_->options_->compaction_style == kCompactionStyleUniversal) {
+        std::sort(important_files.begin(), important_files.end(), NewestFirstBySeqNo);
+      } else {
         std::sort(important_files.begin(), important_files.end(), NewestFirst);
+      }
     } else {
       // Sanity check to make sure that the files are correctly sorted
 #ifndef NDEBUG
@@ -565,7 +578,7 @@ int Version::PickLevelForMemTableOutput(
         break;
       }
       GetOverlappingInputs(level + 2, &start, &limit, &overlaps);
-      const int64_t sum = TotalFileSize(overlaps);
+      const uint64_t sum = TotalFileSize(overlaps);
       if (sum > vset_->MaxGrandParentOverlapBytes(level)) {
         break;
       }
@@ -1109,7 +1122,10 @@ void VersionSet::Init(int num_levels) {
   int target_file_size_multiplier = options_->target_file_size_multiplier;
   int max_bytes_multiplier = options_->max_bytes_for_level_multiplier;
   for (int i = 0; i < num_levels; i++) {
-    if (i > 1) {
+    if (i == 0 && options_->compaction_style == kCompactionStyleUniversal) {
+      max_file_size_[i] = ULLONG_MAX;
+      level_max_bytes_[i] = options_->max_bytes_for_level_base;
+    } else if (i > 1) {
       max_file_size_[i] = max_file_size_[i-1] * target_file_size_multiplier;
       level_max_bytes_[i] = level_max_bytes_[i-1] * max_bytes_multiplier *
         options_->max_bytes_for_level_multiplier_additional[i-1];
@@ -1656,17 +1672,32 @@ void VersionSet::Finalize(Version* v,
   }
 }
 
-// a static compator used to sort files based on their size
+// A static compator used to sort files based on their size
-static bool compareSize(const VersionSet::Fsize& first,
+// In normal mode: descending size
+static bool compareSizeDescending(const VersionSet::Fsize& first,
   const VersionSet::Fsize& second) {
   return (first.file->file_size > second.file->file_size);
 }
+// A static compator used to sort files based on their seqno
+// In universal style : descending seqno
+static bool compareSeqnoDescending(const VersionSet::Fsize& first,
+  const VersionSet::Fsize& second) {
+  if (first.file->smallest_seqno > second.file->smallest_seqno) {
+    assert(first.file->largest_seqno > second.file->largest_seqno);
+    return true;
+  }
+  assert(first.file->largest_seqno <= second.file->largest_seqno);
+  return false;
+}
 
 // sort all files in level1 to level(n-1) based on file size
 void VersionSet::UpdateFilesBySize(Version* v) {
 
   // No need to sort the highest level because it is never compacted.
-  for (int level = 0; level < NumberLevels()-1; level++) {
+  int max_level = (options_->compaction_style == kCompactionStyleUniversal) ?
+                  NumberLevels() : NumberLevels() - 1;
+
+  for (int level = 0; level < max_level; level++) {
 
     const std::vector<FileMetaData*>& files = v->files_[level];
     std::vector<int>& files_by_size = v->files_by_size_[level];
@@ -1680,12 +1711,18 @@ void VersionSet::UpdateFilesBySize(Version* v) {
     }
 
     // sort the top number_of_files_to_sort_ based on file size
+    if (options_->compaction_style == kCompactionStyleUniversal) {
+      int num = temp.size();
+      std::partial_sort(temp.begin(),  temp.begin() + num,
+                        temp.end(), compareSeqnoDescending);
+    } else {
       int num = Version::number_of_files_to_sort_;
       if (num > (int)temp.size()) {
         num = temp.size();
       }
       std::partial_sort(temp.begin(),  temp.begin() + num,
-                      temp.end(), compareSize);
+                        temp.end(), compareSizeDescending);
+    }
     assert(temp.size() == files.size());
 
     // initialize files_by_size_
@@ -1718,7 +1755,8 @@ Status VersionSet::WriteSnapshot(log::Writer* log) {
     const std::vector<FileMetaData*>& files = current_->files_[level];
     for (size_t i = 0; i < files.size(); i++) {
       const FileMetaData* f = files[i];
-      edit.AddFile(level, f->number, f->file_size, f->smallest, f->largest);
+      edit.AddFile(level, f->number, f->file_size, f->smallest, f->largest,
+                   f->smallest_seqno, f->largest_seqno);
     }
   }
 
@@ -1762,6 +1800,23 @@ const char* VersionSet::LevelDataSizeSummary(
   return scratch->buffer;
 }
 
+const char* VersionSet::LevelFileSummary(
+    FileSummaryStorage* scratch, int level) const {
+  int len = snprintf(scratch->buffer, sizeof(scratch->buffer), "files_size[");
+  for (unsigned int i = 0; i < current_->files_[level].size(); i++) {
+    FileMetaData* f = current_->files_[level][i];
+    int sz = sizeof(scratch->buffer) - len;
+    int ret = snprintf(scratch->buffer + len, sz, "#%ld(seq=%ld,sz=%ld,%d) ",
+                       f->number, f->smallest_seqno,
+                       f->file_size, f->being_compacted);
+    if (ret < 0 || ret >= sz)
+      break;
+    len += ret;
+  }
+  snprintf(scratch->buffer + len, sizeof(scratch->buffer) - len, "]");
+  return scratch->buffer;
+}
+
 // Opens the mainfest file and reads all records
 // till it finds the record we are looking for.
 bool VersionSet::ManifestContains(const std::string& record) const {
@@ -1867,14 +1922,14 @@ int64_t VersionSet::NumLevelBytes(int level) const {
 }
 
 int64_t VersionSet::MaxNextLevelOverlappingBytes() {
-  int64_t result = 0;
+  uint64_t result = 0;
   std::vector<FileMetaData*> overlaps;
   for (int level = 1; level < NumberLevels() - 1; level++) {
     for (size_t i = 0; i < current_->files_[level].size(); i++) {
       const FileMetaData* f = current_->files_[level][i];
       current_->GetOverlappingInputs(level+1, &f->smallest, &f->largest,
                                      &overlaps);
-      const int64_t sum = TotalFileSize(overlaps);
+      const uint64_t sum = TotalFileSize(overlaps);
       if (sum > result) {
         result = sum;
       }
@@ -1970,13 +2025,13 @@ uint64_t VersionSet::MaxFileSizeForLevel(int level) {
   return max_file_size_[level];
 }
 
-int64_t VersionSet::ExpandedCompactionByteSizeLimit(int level) {
+uint64_t VersionSet::ExpandedCompactionByteSizeLimit(int level) {
   uint64_t result = MaxFileSizeForLevel(level);
   result *= options_->expanded_compaction_factor;
   return result;
 }
 
-int64_t VersionSet::MaxGrandParentOverlapBytes(int level) {
+uint64_t VersionSet::MaxGrandParentOverlapBytes(int level) {
   uint64_t result = MaxFileSizeForLevel(level);
   result *= options_->max_grandparent_overlap_factor;
   return result;
@@ -2059,6 +2114,176 @@ void VersionSet::SizeBeingCompacted(std::vector<uint64_t>& sizes) {
   }
 }
 
+Compaction* VersionSet::PickCompactionUniversal(int level, double score) {
+  assert (level == 0);
+
+  // percentage flexibilty while comparing file sizes
+  uint64_t ratio = options_->compaction_options_universal.size_ratio;
+  unsigned int min_merge_width =
+    options_->compaction_options_universal.min_merge_width;
+  unsigned int max_merge_width =
+    options_->compaction_options_universal.max_merge_width;
+
+  if ((current_->files_[level].size() <=
+      (unsigned int)options_->level0_file_num_compaction_trigger)) {
+    Log(options_->info_log, "Universal: nothing to do\n");
+    return nullptr;
+  }
+  VersionSet::FileSummaryStorage tmp;
+  Log(options_->info_log, "Universal: candidate files(%lu): %s\n",
+      current_->files_[level].size(),
+      LevelFileSummary(&tmp, 0));
+
+  Compaction* c = nullptr;
+  c = new Compaction(level, level, MaxFileSizeForLevel(level),
+                     LLONG_MAX, NumberLevels());
+  c->score_ = score;
+
+  // The files are sorted from newest first to oldest last.
+  std::vector<int>& file_by_time = current_->files_by_size_[level];
+  FileMetaData* f = nullptr;
+  bool done = false;
+  assert(file_by_time.size() == current_->files_[level].size());
+
+  unsigned int max_files_to_compact = std::min(max_merge_width, UINT_MAX);
+
+  // Make two pass. The first pass considers a candidate file
+  // only if it is smaller than the total size accumulated so far.
+  // The second pass does not look at the slope of the
+  // file-size  curve to decide what to pick for compaction.
+  for (int iter = 0; !done && iter < 2; iter++) {
+
+    for (unsigned int loop = 0; loop < file_by_time.size(); ) {
+
+      // Skip files that are already being compacted
+      for (f = nullptr; loop < file_by_time.size(); loop++) {
+        int index = file_by_time[loop];
+        f = current_->files_[level][index];
+
+        if (!f->being_compacted) {
+          break;
+        }
+        Log(options_->info_log, "Universal: file %ld[%d] being compacted, skipping",
+            f->number, loop);
+        f = nullptr;
+      }
+
+      // This file is not being compacted. Consider it as the
+      // first candidate to be compacted.
+      unsigned int candidate_count = 1;
+      uint64_t candidate_size =  f != nullptr? f->file_size : 0;
+      if (f != nullptr) {
+        Log(options_->info_log, "Universal: Possible candidate file %ld[%d] %s.",
+            f->number, loop, iter == 0? "" : "forced ");
+      }
+
+      // Check if the suceeding files need compaction.
+      for (unsigned int i = loop+1;
+           candidate_count < max_files_to_compact && i < file_by_time.size();
+           i++) {
+        int index = file_by_time[i];
+        FileMetaData* f = current_->files_[level][index];
+        if (f->being_compacted) {
+          break;
+        }
+        // If this is the first iteration, then we pick files if the
+        // total candidate file size (increased by the specified ratio)
+        // is still larger than the next candidate file.
+        if (iter == 0) {
+          uint64_t sz = (candidate_size * (100 + ratio)) /100;
+          if (sz < f->file_size) {
+            break;
+          }
+        }
+        candidate_count++;
+        candidate_size += f->file_size;
+      }
+
+      // Found a series of consecutive files that need compaction.
+      if (candidate_count >= (unsigned int)min_merge_width) {
+        for (unsigned int i = loop; i < loop + candidate_count; i++) {
+          int index = file_by_time[i];
+          FileMetaData* f = current_->files_[level][index];
+          c->inputs_[0].push_back(f);
+          Log(options_->info_log, "Universal: Picking file %ld[%d] with size %ld %s",
+              f->number, i, f->file_size,
+              (iter == 0 ? "" : "forced"));
+        }
+        done = true;
+        break;
+      } else {
+        for (unsigned int i = loop;
+             i < loop + candidate_count && i < file_by_time.size(); i++) {
+         int index = file_by_time[i];
+         FileMetaData* f = current_->files_[level][index];
+         Log(options_->info_log, "Universal: Skipping file %ld[%d] with size %ld %d %s",
+             f->number, i, f->file_size, f->being_compacted,
+              (iter == 0 ? "" : "forced"));
+        }
+      }
+      loop += candidate_count;
+    }
+    assert(done || c->inputs_[0].size() == 0);
+
+    // If we are unable to find a normal compaction run and we are still
+    // above the compaction threshold, iterate again to pick compaction
+    // candidates, this time without considering their size differences.
+    if (!done) {
+      int files_not_in_compaction = 0;
+      for (unsigned int i = 0; i < current_->files_[level].size(); i++) {
+        f = current_->files_[level][i];
+        if (!f->being_compacted) {
+          files_not_in_compaction++;
+        }
+      }
+      int expected_num_files = files_not_in_compaction +
+                compactions_in_progress_[level].size();
+      if (expected_num_files <=
+          options_->level0_file_num_compaction_trigger + 1) {
+        done = true;     // nothing more to do
+      } else {
+        max_files_to_compact = std::min((int)max_merge_width,
+          expected_num_files - options_->level0_file_num_compaction_trigger);
+        Log(options_->info_log, "Universal: second loop with maxfiles %d",
+            max_files_to_compact);
+      }
+    }
+  }
+  if (c->inputs_[0].size() <= 1) {
+    Log(options_->info_log, "Universal: only %ld files, nothing to do.\n",
+        c->inputs_[0].size());
+    delete c;
+    return nullptr;
+  }
+
+  // validate that all the chosen files are non overlapping in time
+  FileMetaData* newerfile __attribute__((unused)) = nullptr;
+  for (unsigned int i = 0; i < c->inputs_[0].size(); i++) {
+    FileMetaData* f = c->inputs_[0][i];
+    assert (f->smallest_seqno <= f->largest_seqno);
+    assert(newerfile == nullptr ||
+           newerfile->smallest_seqno > f->largest_seqno);
+    newerfile = f;
+  }
+
+  // update statistics
+  if (options_->statistics != nullptr) {
+    options_->statistics->measureTime(NUM_FILES_IN_SINGLE_COMPACTION,
+                                      c->inputs_[0].size());
+  }
+
+  c->input_version_ = current_;
+  c->input_version_->Ref();
+
+  // mark all the files that are being compacted
+  c->MarkFilesBeingCompacted(true);
+
+  // remember this currently undergoing compaction
+  compactions_in_progress_[level].insert(c);
+
+  return c;
+}
+
 Compaction* VersionSet::PickCompactionBySize(int level, double score) {
   Compaction* c = nullptr;
 
@@ -2072,7 +2297,7 @@ Compaction* VersionSet::PickCompactionBySize(int level, double score) {
 
   assert(level >= 0);
   assert(level+1 < NumberLevels());
-  c = new Compaction(level, MaxFileSizeForLevel(level+1),
+  c = new Compaction(level, level+1, MaxFileSizeForLevel(level+1),
       MaxGrandParentOverlapBytes(level), NumberLevels());
   c->score_ = score;
 
@@ -2142,6 +2367,13 @@ Compaction* VersionSet::PickCompaction() {
   current_->vset_->SizeBeingCompacted(size_being_compacted);
   Finalize(current_, size_being_compacted);
 
+  // In universal style of compaction, compact L0 files back into L0.
+  if (options_->compaction_style ==  kCompactionStyleUniversal) {
+    int level = 0;
+    c = PickCompactionUniversal(level, current_->compaction_score_[level]);
+    return c;
+  }
+
   // We prefer compactions triggered by too much data in a level over
   // the compactions triggered by seeks.
   //
@@ -2169,9 +2401,9 @@ Compaction* VersionSet::PickCompaction() {
     // Only allow one level 0 compaction at a time.
     // Do not pick this file if its parents at level+1 are being compacted.
     if (level != 0 || compactions_in_progress_[0].empty()) {
-      if (!ParentRangeInCompaction(&f->smallest, &f->largest, level,
+      if(!ParentRangeInCompaction(&f->smallest, &f->largest, level,
                                   &parent_index)) {
-        c = new Compaction(level, MaxFileSizeForLevel(level+1),
+        c = new Compaction(level, level, MaxFileSizeForLevel(level+1),
                 MaxGrandParentOverlapBytes(level), NumberLevels(), true);
         c->inputs_[0].push_back(f);
         c->parent_index_ = parent_index;
@@ -2331,10 +2563,10 @@ void VersionSet::SetupOtherInputs(Compaction* c) {
     std::vector<FileMetaData*> expanded0;
     current_->GetOverlappingInputs(level, &all_start, &all_limit, &expanded0,
                                    c->base_index_, nullptr);
-    const int64_t inputs0_size = TotalFileSize(c->inputs_[0]);
+    const uint64_t inputs0_size = TotalFileSize(c->inputs_[0]);
-    const int64_t inputs1_size = TotalFileSize(c->inputs_[1]);
+    const uint64_t inputs1_size = TotalFileSize(c->inputs_[1]);
-    const int64_t expanded0_size = TotalFileSize(expanded0);
+    const uint64_t expanded0_size = TotalFileSize(expanded0);
-    int64_t limit = ExpandedCompactionByteSizeLimit(level);
+    uint64_t limit = ExpandedCompactionByteSizeLimit(level);
     if (expanded0.size() > c->inputs_[0].size() &&
         inputs1_size + expanded0_size < limit &&
         !FilesInCompaction(expanded0) &&
@@ -2414,7 +2646,10 @@ Compaction* VersionSet::CompactRange(
       }
     }
   }
-  Compaction* c = new Compaction(level, MaxFileSizeForLevel(level+1),
+  int out_level = (options_->compaction_style == kCompactionStyleUniversal) ?
+                  level : level+1;
+
+  Compaction* c = new Compaction(level, out_level, MaxFileSizeForLevel(out_level),
     MaxGrandParentOverlapBytes(level), NumberLevels());
 
   c->inputs_[0] = inputs;
@@ -2435,10 +2670,11 @@ Compaction* VersionSet::CompactRange(
   return c;
 }
 
-Compaction::Compaction(int level, uint64_t target_file_size,
+Compaction::Compaction(int level, int out_level, uint64_t target_file_size,
   uint64_t max_grandparent_overlap_bytes, int number_levels,
   bool seek_compaction)
     : level_(level),
+      out_level_(out_level),
       max_output_file_size_(target_file_size),
       maxGrandParentOverlapBytes_(max_grandparent_overlap_bytes),
       input_version_(nullptr),

db/version_set.h

@@ -352,6 +352,9 @@ class VersionSet {
   struct LevelSummaryStorage {
     char buffer[100];
   };
+  struct FileSummaryStorage {
+    char buffer[1000];
+  };
   const char* LevelSummary(LevelSummaryStorage* scratch) const;
 
   // printf contents (for debugging)
@@ -362,6 +365,10 @@ class VersionSet {
   // of files per level.  Uses *scratch as backing store.
   const char* LevelDataSizeSummary(LevelSummaryStorage* scratch) const;
 
+  // Return a human-readable short (single-line) summary of files
+  // in a specified level.  Uses *scratch as backing store.
+  const char* LevelFileSummary(FileSummaryStorage* scratch, int level) const;
+
   // Return the size of the current manifest file
   const uint64_t ManifestFileSize() { return current_->offset_manifest_file_; }
 
@@ -371,6 +378,9 @@ class VersionSet {
   // function will return nullptr.
   Compaction* PickCompactionBySize(int level, double score);
 
+  // Pick files to compact in Universal mode
+  Compaction* PickCompactionUniversal(int level, double score);
+
   // Free up the files that were participated in a compaction
   void ReleaseCompactionFiles(Compaction* c, Status status);
 
@@ -426,9 +436,9 @@ class VersionSet {
 
   bool ManifestContains(const std::string& record) const;
 
-  int64_t ExpandedCompactionByteSizeLimit(int level);
+  uint64_t ExpandedCompactionByteSizeLimit(int level);
 
-  int64_t MaxGrandParentOverlapBytes(int level);
+  uint64_t MaxGrandParentOverlapBytes(int level);
 
   Env* const env_;
   const std::string dbname_;
@@ -503,9 +513,12 @@ class Compaction {
   ~Compaction();
 
   // Return the level that is being compacted.  Inputs from "level"
-  // and "level+1" will be merged to produce a set of "level+1" files.
+  // will be merged.
   int level() const { return level_; }
 
+  // Outputs will go to this level
+  int output_level() const { return out_level_; }
+
   // Return the object that holds the edits to the descriptor done
   // by this compaction.
   VersionEdit* edit() { return edit_; }
@@ -548,13 +561,14 @@ class Compaction {
   friend class Version;
   friend class VersionSet;
 
-  explicit Compaction(int level, uint64_t target_file_size,
+  explicit Compaction(int level, int out_level, uint64_t target_file_size,
     uint64_t max_grandparent_overlap_bytes, int number_levels,
     bool seek_compaction = false);
 
   int level_;
+  int out_level_; // levels to which output files are stored
   uint64_t max_output_file_size_;
-  int64_t maxGrandParentOverlapBytes_;
+  uint64_t maxGrandParentOverlapBytes_;
   Version* input_version_;
   VersionEdit* edit_;
   int number_levels_;
@@ -569,7 +583,7 @@ class Compaction {
   std::vector<FileMetaData*> grandparents_;
   size_t grandparent_index_;  // Index in grandparent_starts_
   bool seen_key_;             // Some output key has been seen
-  int64_t overlapped_bytes_;  // Bytes of overlap between current output
+  uint64_t overlapped_bytes_;  // Bytes of overlap between current output
                               // and grandparent files
   int base_index_;   // index of the file in files_[level_]
   int parent_index_; // index of some file with same range in files_[level_+1]

include/leveldb/options.h

@@ -12,6 +12,7 @@
 #include <stdint.h>
 #include "leveldb/slice.h"
 #include "leveldb/statistics.h"
+#include "leveldb/universal_compaction.h"
 #include "leveldb/memtablerep.h"
 
 namespace leveldb {
@@ -40,6 +41,11 @@ enum CompressionType {
   kBZip2Compression = 0x3
 };
 
+enum CompactionStyle {
+  kCompactionStyleLevel       = 0x0, // level based compaction style
+  kCompactionStyleUniversal   = 0x1  // Universal compaction style
+};
+
 // Compression options for different compression algorithms like Zlib
 struct CompressionOptions {
   int window_bits;
@@ -483,6 +489,12 @@ struct Options {
   // Default: 0
   uint64_t bytes_per_sync;
 
+  // The compaction style. Default: kCompactionStyleLevel
+  CompactionStyle compaction_style;
+
+  // The options needed to support Universal Style compactions
+  CompactionOptionsUniversal compaction_options_universal;
+
   // Use KeyMayExist API to filter deletes when this is true.
   // If KeyMayExist returns false, i.e. the key definitely does not exist, then
   // the delete is a noop. KeyMayExist only incurs in-memory look up.
@@ -494,7 +506,6 @@ struct Options {
   // Default: a factory that provides a skip-list-based implementation of
   // MemTableRep.
   std::shared_ptr<MemTableRepFactory> memtable_factory;
-
 };
 
 // Options that control read operations

include/leveldb/statistics.h

@@ -115,7 +115,8 @@ enum Histograms {
   STALL_L0_NUM_FILES_COUNT = 14,
   HARD_RATE_LIMIT_DELAY_COUNT = 15,
   SOFT_RATE_LIMIT_DELAY_COUNT = 16,
-  HISTOGRAM_ENUM_MAX = 17
+  NUM_FILES_IN_SINGLE_COMPACTION = 17,
+  HISTOGRAM_ENUM_MAX = 18
 };
 
 const std::vector<std::pair<Histograms, std::string>> HistogramsNameMap = {
@@ -135,7 +136,8 @@ const std::vector<std::pair<Histograms, std::string>> HistogramsNameMap = {
   { STALL_MEMTABLE_COMPACTION_COUNT, "rocksdb.memtable.compaction.count"},
   { STALL_L0_NUM_FILES_COUNT, "rocksdb.num.files.stall.count"},
   { HARD_RATE_LIMIT_DELAY_COUNT, "rocksdb.hard.rate.limit.delay.count"},
-  { SOFT_RATE_LIMIT_DELAY_COUNT, "rocksdb.soft.rate.limit.delay.count"}
+  { SOFT_RATE_LIMIT_DELAY_COUNT, "rocksdb.soft.rate.limit.delay.count"},
+  { NUM_FILES_IN_SINGLE_COMPACTION, "rocksdb.numfiles.in.singlecompaction" }
 };
 
 struct HistogramData {

include/leveldb/universal_compaction.h

@@ -0,0 +1,57 @@
+// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file. See the AUTHORS file for names of contributors.
+
+#ifndef STORAGE_ROCKSDB_UNIVERSAL_COMPACTION_OPTIONS_H
+#define STORAGE_ROCKSDB_UNIVERSAL_COMPACTION_OPTIONS_H
+
+#include <stddef.h>
+#include <string>
+#include <memory>
+#include <vector>
+#include <stdint.h>
+#include <climits>
+#include "leveldb/slice.h"
+#include "leveldb/statistics.h"
+
+namespace leveldb {
+
+//
+// Algorithm used to make a compaction request stop picking new files
+// into a single compaction run
+//
+enum CompactionStopStyle {
+  kCompactionStopStyleSimilarSize, // pick files of similar size
+  kCompactionStopStyleTotalSize    // total size of picked files > next file
+};
+
+class CompactionOptionsUniversal {
+ public:
+
+  // Percentage flexibilty while comparing file size. If the candidate file(s)
+  // size is 1% smaller than the next file's size, then include next file into
+  // this candidate set. // Default: 1
+  unsigned int size_ratio;
+
+  // The minimum number of files in a single compaction run. Default: 2
+  unsigned int min_merge_width;
+
+  // The maximum number of files in a single compaction run. Default: INT_MAX
+  unsigned int max_merge_width;
+
+  // The algorithm used to stop picking files into a single compaction run
+  // Default: kCompactionStopStyleTotalSize
+  CompactionStopStyle stop_style;
+
+  // Default set of parameters
+  CompactionOptionsUniversal() :
+    size_ratio(1),
+    min_merge_width(2),
+    max_merge_width(UINT_MAX),
+    stop_style(kCompactionStopStyleTotalSize) {
+  }
+};
+
+}  // namespace leveldb
+
+#endif  // STORAGE_ROCKSDB_UNIVERSAL_COMPACTION_OPTIONS_H

tools/db_stress.cc

@@ -88,6 +88,9 @@ static int FLAGS_max_write_buffer_number = 0;
 // This is initialized to default value of 1 in "main" function.
 static int FLAGS_max_background_compactions = 0;
 
+// This is initialized to default value of false
+static leveldb::CompactionStyle FLAGS_compaction_style = leveldb::kCompactionStyleLevel;
+
 // Number of bytes to use as a cache of uncompressed data.
 static long FLAGS_cache_size = 2 * KB * KB * KB;
 
@@ -935,6 +938,7 @@ class StressTest {
     options.write_buffer_size = FLAGS_write_buffer_size;
     options.max_write_buffer_number = FLAGS_max_write_buffer_number;
     options.max_background_compactions = FLAGS_max_background_compactions;
+    options.compaction_style = FLAGS_compaction_style;
     options.block_size = FLAGS_block_size;
     options.filter_policy = filter_policy_;
     options.max_open_files = FLAGS_open_files;
@@ -1021,6 +1025,8 @@ int main(int argc, char** argv) {
   FLAGS_open_files = leveldb::Options().max_open_files;
   FLAGS_max_background_compactions =
     leveldb::Options().max_background_compactions;
+  FLAGS_compaction_style =
+    leveldb::Options().compaction_style;
   FLAGS_level0_file_num_compaction_trigger =
     leveldb::Options().level0_file_num_compaction_trigger;
   FLAGS_level0_slowdown_writes_trigger =
@@ -1073,6 +1079,8 @@ int main(int argc, char** argv) {
       FLAGS_max_write_buffer_number = n;
     } else if (sscanf(argv[i], "--max_background_compactions=%d%c", &n, &junk) == 1) {
       FLAGS_max_background_compactions = n;
+    } else if (sscanf(argv[i], "--compaction_style=%d%c", &n, &junk) == 1) {
+      FLAGS_compaction_style = (leveldb::CompactionStyle)n;
     } else if (sscanf(argv[i], "--cache_size=%ld%c", &l, &junk) == 1) {
       FLAGS_cache_size = l;
     } else if (sscanf(argv[i], "--block_size=%d%c", &n, &junk) == 1) {

util/ldb_cmd.cc

@@ -1197,7 +1197,7 @@ void ApproxSizeCommand::DoCommand() {
   uint64_t sizes[1];
   db_->GetApproximateSizes(ranges, 1, sizes);
   fprintf(stdout, "%ld\n", sizes[0]);
-  /* Wierd that GetApproximateSizes() returns void, although documentation
+  /* Weird that GetApproximateSizes() returns void, although documentation
    * says that it returns a Status object.
   if (!st.ok()) {
     exec_state_ = LDBCommandExecuteResult::FAILED(st.ToString());

util/options.cc

@@ -78,6 +78,7 @@ Options::Options()
       access_hint_on_compaction_start(NORMAL),
       use_adaptive_mutex(false),
       bytes_per_sync(0),
+      compaction_style(kCompactionStyleLevel),
       filter_deletes(false),
       memtable_factory(std::shared_ptr<SkipListFactory>(new SkipListFactory)) {
   assert(memtable_factory.get() != nullptr);
@@ -218,6 +219,14 @@ Options::Dump(Logger* log) const
         bytes_per_sync);
     Log(log,"                          Options.filter_deletes: %d",
         filter_deletes);
+    Log(log,"                        Options.compaction_style: %d",
+        compaction_style);
+    Log(log,"        Options.compaction_options_universal.size_ratio: %d",
+        compaction_options_universal.size_ratio);
+    Log(log,"   Options.compaction_options_universal.min_merge_width: %d",
+        compaction_options_universal.min_merge_width);
+    Log(log,"   Options.compaction_options_universal.max_merge_width: %d",
+        compaction_options_universal.max_merge_width);
 }   // Options::Dump
 
 //