Support multiple DB directories in universal compaction style

Summary:
This patch adds a target size parameter in options.db_paths and universal compaction will base it to determine which DB path to place a new file.
Level-style stays the same.

Test Plan: Add new unit tests

Reviewers: ljin, yhchiang

Reviewed By: yhchiang

Subscribers: MarkCallaghan, dhruba, igor, leveldb

Differential Revision: https://reviews.facebook.net/D19869

HISTORY.md

@@ -1,5 +1,13 @@
 # Rocksdb Change Log
 
+### Unrelease
+### New Features
+* Support Multiple DB paths in universal style compactions
+
+### Public API changes
+* DBOptions.db_paths now is a vector of a DBPath structure which indicates both of path and target size
+
+
 ## 3.3.0 (7/10/2014)
 ### New Features
 * Added JSON API prototype.

db/compaction_picker.cc

@@ -635,6 +635,37 @@ Compaction* UniversalCompactionPicker::PickCompaction(Version* version,
   return c;
 }
 
+uint32_t UniversalCompactionPicker::GetPathId(const Options& options,
+                                              uint64_t file_size) {
+  // Two conditions need to be satisfied:
+  // (1) the target path needs to be able to hold the file's size
+  // (2) Total size left in this and previous paths need to be not
+  //     smaller than expected future file size before this new file is
+  //     compacted, which is estimated based on size_ratio.
+  // For example, if now we are compacting files of size (1, 1, 2, 4, 8),
+  // we will make sure the target file, probably with size of 16, will be
+  // placed in a path so that eventually when new files are generated and
+  // compacted to (1, 1, 2, 4, 8, 16), all those files can be stored in or
+  // before the path we chose.
+  //
+  // TODO(sdong): now the case of multiple column families is not
+  // considered in this algorithm. So the target size can be violated in
+  // that case. We need to improve it.
+  uint64_t accumulated_size = 0;
+  uint64_t future_size =
+      file_size * (100 - options.compaction_options_universal.size_ratio) / 100;
+  uint32_t p = 0;
+  for (; p < options.db_paths.size() - 1; p++) {
+    uint64_t target_size = options.db_paths[p].target_size;
+    if (target_size > file_size &&
+        accumulated_size + (target_size - file_size) > future_size) {
+      return p;
+    }
+    accumulated_size += target_size;
+  }
+  return p;
+}
+
 //
 // Consider compaction files based on their size differences with
 // the next file in time order.
@@ -765,8 +796,15 @@ Compaction* UniversalCompactionPicker::PickCompactionUniversalReadAmp(
       }
     }
   }
+
+  uint64_t estimated_total_size = 0;
+  for (unsigned int i = 0; i < first_index_after; i++) {
+    estimated_total_size += files[i]->fd.GetFileSize();
+  }
+  uint32_t path_id = GetPathId(*options_, estimated_total_size);
+
   Compaction* c = new Compaction(
-      version, level, level, MaxFileSizeForLevel(level), LLONG_MAX, 0,
+      version, level, level, MaxFileSizeForLevel(level), LLONG_MAX, path_id,
       GetCompressionType(*options_, level, enable_compression));
   c->score_ = score;
 
@@ -865,11 +903,18 @@ Compaction* UniversalCompactionPicker::PickCompactionUniversalSizeAmp(
   }
   assert(start_index >= 0 && start_index < files.size() - 1);
 
+  // Estimate total file size
+  uint64_t estimated_total_size = 0;
+  for (unsigned int loop = start_index; loop < files.size(); loop++) {
+    estimated_total_size += files[loop]->fd.GetFileSize();
+  }
+  uint32_t path_id = GetPathId(*options_, estimated_total_size);
+
   // create a compaction request
   // We always compact all the files, so always compress.
   Compaction* c =
       new Compaction(version, level, level, MaxFileSizeForLevel(level),
-                     LLONG_MAX, 0, GetCompressionType(*options_, level));
+                     LLONG_MAX, path_id, GetCompressionType(*options_, level));
   c->score_ = score;
   for (unsigned int loop = start_index; loop < files.size(); loop++) {
     f = c->input_version_->files_[level][loop];

db/compaction_picker.h

@@ -145,6 +145,10 @@ class UniversalCompactionPicker : public CompactionPicker {
   // Pick Universal compaction to limit space amplification.
   Compaction* PickCompactionUniversalSizeAmp(Version* version, double score,
                                              LogBuffer* log_buffer);
+
+  // Pick a path ID to place a newly generated file, with its estimated file
+  // size.
+  static uint32_t GetPathId(const Options& options, uint64_t file_size);
 };
 
 class LevelCompactionPicker : public CompactionPicker {

db/db_impl.cc

@@ -299,7 +299,7 @@ DBOptions SanitizeOptions(const std::string& dbname, const DBOptions& src) {
   }
 
   if (result.db_paths.size() == 0) {
-    result.db_paths.push_back(dbname);
+    result.db_paths.emplace_back(dbname, std::numeric_limits<uint64_t>::max());
   }
 
   return result;
@@ -1105,8 +1105,8 @@ Status DBImpl::Recover(
       return s;
     }
 
-    for (auto db_path : options_.db_paths) {
-      s = env_->CreateDirIfMissing(db_path);
+    for (auto& db_path : options_.db_paths) {
+      s = env_->CreateDirIfMissing(db_path.path);
       if (!s.ok()) {
         return s;
       }
@@ -4609,8 +4609,18 @@ Status DB::Open(const DBOptions& db_options, const std::string& dbname,
                 const std::vector<ColumnFamilyDescriptor>& column_families,
                 std::vector<ColumnFamilyHandle*>* handles, DB** dbptr) {
   if (db_options.db_paths.size() > 1) {
-    return Status::NotSupported(
-        "More than one DB paths are not supported yet. ");
+    for (auto& cfd : column_families) {
+      if (cfd.options.compaction_style != kCompactionStyleUniversal) {
+        return Status::NotSupported(
+            "More than one DB paths are only supported in "
+            "universal compaction style. ");
+      }
+    }
+
+    if (db_options.db_paths.size() > 4) {
+      return Status::NotSupported(
+        "More than four DB paths are not supported yet. ");
+    }
   }
 
   *dbptr = nullptr;
@@ -4629,8 +4639,8 @@ Status DB::Open(const DBOptions& db_options, const std::string& dbname,
   DBImpl* impl = new DBImpl(db_options, dbname);
   Status s = impl->env_->CreateDirIfMissing(impl->options_.wal_dir);
   if (s.ok()) {
-    for (auto path : impl->options_.db_paths) {
-      s = impl->env_->CreateDirIfMissing(path);
+    for (auto db_path : impl->options_.db_paths) {
+      s = impl->env_->CreateDirIfMissing(db_path.path);
       if (!s.ok()) {
         break;
       }
@@ -4798,14 +4808,14 @@ Status DestroyDB(const std::string& dbname, const Options& options) {
       }
     }
 
-    for (auto db_path : options.db_paths) {
-      env->GetChildren(db_path, &filenames);
+    for (auto& db_path : options.db_paths) {
+      env->GetChildren(db_path.path, &filenames);
       uint64_t number;
       FileType type;
       for (size_t i = 0; i < filenames.size(); i++) {
         if (ParseFileName(filenames[i], &number, &type) &&
             type == kTableFile) {  // Lock file will be deleted at end
-          Status del = env->DeleteFile(db_path + "/" + filenames[i]);
+          Status del = env->DeleteFile(db_path.path + "/" + filenames[i]);
           if (result.ok() && !del.ok()) {
             result = del;
           }

db/db_test.cc

@@ -370,8 +370,10 @@ class DBTest {
   ~DBTest() {
     Close();
     Options options;
-    options.db_paths.push_back(dbname_);
-    options.db_paths.push_back(dbname_ + "_2");
+    options.db_paths.emplace_back(dbname_, 0);
+    options.db_paths.emplace_back(dbname_ + "_2", 0);
+    options.db_paths.emplace_back(dbname_ + "_3", 0);
+    options.db_paths.emplace_back(dbname_ + "_4", 0);
     ASSERT_OK(DestroyDB(dbname_, options));
     delete env_;
     delete filter_policy_;
@@ -3474,10 +3476,206 @@ TEST(DBTest, UniversalCompactionCompressRatio2) {
 
 TEST(DBTest, FailMoreDbPaths) {
   Options options;
-  options.db_paths.push_back(dbname_);
-  options.db_paths.push_back(dbname_ + "_2");
+  options.db_paths.emplace_back(dbname_, 10000000);
+  options.db_paths.emplace_back(dbname_ + "_2", 1000000);
+  options.db_paths.emplace_back(dbname_ + "_3", 1000000);
+  options.db_paths.emplace_back(dbname_ + "_4", 1000000);
+  options.db_paths.emplace_back(dbname_ + "_5", 1000000);
   ASSERT_TRUE(TryReopen(&options).IsNotSupported());
 }
+
+TEST(DBTest, UniversalCompactionSecondPathRatio) {
+  Options options;
+  options.db_paths.emplace_back(dbname_, 500 * 1024);
+  options.db_paths.emplace_back(dbname_ + "_2", 1024 * 1024 * 1024);
+  options.compaction_style = kCompactionStyleUniversal;
+  options.write_buffer_size = 100 << 10;  // 100KB
+  options.level0_file_num_compaction_trigger = 2;
+  options.num_levels = 1;
+  options = CurrentOptions(options);
+
+  std::vector<std::string> filenames;
+  env_->GetChildren(options.db_paths[1].path, &filenames);
+  // Delete archival files.
+  for (size_t i = 0; i < filenames.size(); ++i) {
+    env_->DeleteFile(options.db_paths[1].path + "/" + filenames[i]);
+  }
+  env_->DeleteDir(options.db_paths[1].path);
+  Reopen(&options);
+
+  Random rnd(301);
+  int key_idx = 0;
+
+  // First three 110KB files are not going to second path.
+  // After that, (100K, 200K)
+  for (int num = 0; num < 3; num++) {
+    GenerateNewFile(&rnd, &key_idx);
+  }
+
+  // Another 110KB triggers a compaction to 400K file to second path
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[1].path));
+
+  // (1, 4)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[1].path));
+  ASSERT_EQ(1, GetSstFileCount(dbname_));
+
+  // (1,1,4) -> (2, 4)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[1].path));
+  ASSERT_EQ(1, GetSstFileCount(dbname_));
+
+  // (1, 2, 4)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[1].path));
+  ASSERT_EQ(2, GetSstFileCount(dbname_));
+
+  // (1, 1, 2, 4) -> (8)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[1].path));
+  ASSERT_EQ(0, GetSstFileCount(dbname_));
+
+  // (1, 8)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[1].path));
+  ASSERT_EQ(1, GetSstFileCount(dbname_));
+
+  // (1, 1, 8) -> (2, 8)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[1].path));
+  ASSERT_EQ(1, GetSstFileCount(dbname_));
+
+  // (1, 2, 8)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[1].path));
+  ASSERT_EQ(2, GetSstFileCount(dbname_));
+
+  // (1, 1, 2, 8) -> (4, 8)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(2, GetSstFileCount(options.db_paths[1].path));
+  ASSERT_EQ(0, GetSstFileCount(dbname_));
+
+  // (1, 4, 8)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(2, GetSstFileCount(options.db_paths[1].path));
+  ASSERT_EQ(1, GetSstFileCount(dbname_));
+
+  for (int i = 0; i < key_idx; i++) {
+    auto v = Get(Key(i));
+    ASSERT_NE(v, "NOT_FOUND");
+    ASSERT_TRUE(v.size() == 1 || v.size() == 10000);
+  }
+
+  Reopen(&options);
+
+  for (int i = 0; i < key_idx; i++) {
+    auto v = Get(Key(i));
+    ASSERT_NE(v, "NOT_FOUND");
+    ASSERT_TRUE(v.size() == 1 || v.size() == 10000);
+  }
+
+  Destroy(&options);
+}
+
+TEST(DBTest, UniversalCompactionFourPaths) {
+  Options options;
+  options.db_paths.emplace_back(dbname_, 300 * 1024);
+  options.db_paths.emplace_back(dbname_ + "_2", 300 * 1024);
+  options.db_paths.emplace_back(dbname_ + "_3", 500 * 1024);
+  options.db_paths.emplace_back(dbname_ + "_4", 1024 * 1024 * 1024);
+  options.compaction_style = kCompactionStyleUniversal;
+  options.write_buffer_size = 100 << 10;  // 100KB
+  options.level0_file_num_compaction_trigger = 2;
+  options.num_levels = 1;
+  options = CurrentOptions(options);
+
+  std::vector<std::string> filenames;
+  env_->GetChildren(options.db_paths[1].path, &filenames);
+  // Delete archival files.
+  for (size_t i = 0; i < filenames.size(); ++i) {
+    env_->DeleteFile(options.db_paths[1].path + "/" + filenames[i]);
+  }
+  env_->DeleteDir(options.db_paths[1].path);
+  Reopen(&options);
+
+  Random rnd(301);
+  int key_idx = 0;
+
+  // First three 110KB files are not going to second path.
+  // After that, (100K, 200K)
+  for (int num = 0; num < 3; num++) {
+    GenerateNewFile(&rnd, &key_idx);
+  }
+
+  // Another 110KB triggers a compaction to 400K file to second path
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[2].path));
+
+  // (1, 4)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[2].path));
+  ASSERT_EQ(1, GetSstFileCount(dbname_));
+
+  // (1,1,4) -> (2, 4)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[2].path));
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[1].path));
+  ASSERT_EQ(0, GetSstFileCount(dbname_));
+
+  // (1, 2, 4)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[2].path));
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[1].path));
+  ASSERT_EQ(1, GetSstFileCount(dbname_));
+
+  // (1, 1, 2, 4) -> (8)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[3].path));
+
+  // (1, 8)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[3].path));
+  ASSERT_EQ(1, GetSstFileCount(dbname_));
+
+  // (1, 1, 8) -> (2, 8)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[3].path));
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[1].path));
+
+  // (1, 2, 8)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[3].path));
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[1].path));
+  ASSERT_EQ(1, GetSstFileCount(dbname_));
+
+  // (1, 1, 2, 8) -> (4, 8)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[2].path));
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[3].path));
+
+  // (1, 4, 8)
+  GenerateNewFile(&rnd, &key_idx);
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[3].path));
+  ASSERT_EQ(1, GetSstFileCount(options.db_paths[2].path));
+  ASSERT_EQ(1, GetSstFileCount(dbname_));
+
+  for (int i = 0; i < key_idx; i++) {
+    auto v = Get(Key(i));
+    ASSERT_NE(v, "NOT_FOUND");
+    ASSERT_TRUE(v.size() == 1 || v.size() == 10000);
+  }
+
+  Reopen(&options);
+
+  for (int i = 0; i < key_idx; i++) {
+    auto v = Get(Key(i));
+    ASSERT_NE(v, "NOT_FOUND");
+    ASSERT_TRUE(v.size() == 1 || v.size() == 10000);
+  }
+
+  Destroy(&options);
+}
 #endif
 
 TEST(DBTest, ConvertCompactionStyle) {

db/filename.cc

@@ -71,14 +71,14 @@ std::string MakeTableFileName(const std::string& path, uint64_t number) {
   return MakeFileName(path, number, "sst");
 }
 
-std::string TableFileName(const std::vector<std::string> db_paths,
-                          uint64_t number, uint32_t path_id) {
+std::string TableFileName(const std::vector<DbPath>& db_paths, uint64_t number,
+                          uint32_t path_id) {
   assert(number > 0);
   std::string path;
   if (path_id >= db_paths.size()) {
-    path = db_paths.back();
+    path = db_paths.back().path;
   } else {
-    path = db_paths[path_id];
+    path = db_paths[path_id].path;
   }
   return MakeTableFileName(path, number);
 }

db/filename.h

@@ -58,7 +58,7 @@ extern std::string MakeTableFileName(const std::string& name, uint64_t number);
 // Return the name of the sstable with the specified number
 // in the db named by "dbname".  The result will be prefixed with
 // "dbname".
-extern std::string TableFileName(const std::vector<std::string> db_paths,
+extern std::string TableFileName(const std::vector<DbPath>& db_paths,
                                  uint64_t number, uint32_t path_id);
 
 extern std::string FormatFileNumber(uint64_t number, uint32_t path_id);

db/filename_test.cc

@@ -108,8 +108,9 @@ TEST(FileNameTest, Construction) {
   ASSERT_EQ(192U, number);
   ASSERT_EQ(kLogFile, type);
 
-  fname = TableFileName({"bar"}, 200, 0);
-  std::string fname1 = TableFileName({"foo", "bar"}, 200, 1);
+  fname = TableFileName({DbPath("bar", 0)}, 200, 0);
+  std::string fname1 =
+      TableFileName({DbPath("foo", 0), DbPath("bar", 0)}, 200, 1);
   ASSERT_EQ(fname, fname1);
   ASSERT_EQ("bar/", std::string(fname.data(), 4));
   ASSERT_TRUE(ParseFileName(fname.c_str() + 4, &number, &type));

db/repair.cc

@@ -126,7 +126,8 @@ class Repairer {
     std::vector<std::string> filenames;
     bool found_file = false;
     for (uint32_t path_id = 0; path_id < options_.db_paths.size(); path_id++) {
-      Status status = env_->GetChildren(options_.db_paths[path_id], &filenames);
+      Status status =
+          env_->GetChildren(options_.db_paths[path_id].path, &filenames);
       if (!status.ok()) {
         return status;
       }

db/table_cache.h

@@ -85,7 +85,7 @@ class TableCache {
 
  private:
   Env* const env_;
-  const std::vector<std::string> db_paths_;
+  const std::vector<DbPath> db_paths_;
   const Options* options_;
   const EnvOptions& storage_options_;
   Cache* const cache_;

db/version_set.cc

@@ -2857,10 +2857,10 @@ void VersionSet::GetLiveFilesMetaData(std::vector<LiveFileMetaData>* metadata) {
         filemetadata.column_family_name = cfd->GetName();
         uint32_t path_id = file->fd.GetPathId();
         if (path_id < options_->db_paths.size()) {
-          filemetadata.db_path = options_->db_paths[path_id];
+          filemetadata.db_path = options_->db_paths[path_id].path;
         } else {
           assert(!options_->db_paths.empty());
-          filemetadata.db_path = options_->db_paths.back();
+          filemetadata.db_path = options_->db_paths.back().path;
         }
         filemetadata.name = MakeTableFileName("", file->fd.GetNumber());
         filemetadata.level = level;

include/rocksdb/options.h

@@ -83,6 +83,14 @@ enum UpdateStatus {    // Return status For inplace update callback
   UPDATED         = 2, // No inplace update. Merged value set
 };
 
+struct DbPath {
+  std::string path;
+  uint64_t target_size;  // Target size of total files under the path, in byte.
+
+  DbPath() : target_size(0) {}
+  DbPath(const std::string& p, uint64_t t) : path(p), target_size(t) {}
+};
+
 struct Options;
 
 struct ColumnFamilyOptions {
@@ -677,12 +685,31 @@ struct DBOptions {
   // This options is not used!!
   int db_stats_log_interval;
 
-  // A list paths where SST files can be put into. A compaction style can
-  // determine which of those paths it will put the file to.
+  // A list of paths where SST files can be put into, with its target size.
+  // Newer data is placed into paths specified earlier in the vector while
+  // older data gradually moves to paths specified later in the vector.
+  //
+  // For example, you have a flash device with 10GB allocated for the DB,
+  // as well as a hard drive of 2TB, you should config it to be:
+  //   [{"/flash_path", 10GB}, {"/hard_drive", 2TB}]
+  //
+  // The system will try to guarantee data under each path is close to but
+  // not larger than the target size. But current and future file sizes used
+  // by determining where to place a file are based on best-effort estimation,
+  // which means there is a chance that the actual size under the directory
+  // is slightly more than target size under some workloads. User should give
+  // some buffer room for those cases.
+  //
+  // If none of the paths has sufficient room to place a file, the file will
+  // be placed to the last path anyway, despite to the target size.
+  //
+  // Placing newer data to ealier paths is also best-efforts. User should
+  // expect user files to be placed in higher levels in some extreme cases.
+  //
   // If left empty, only one path will be used, which is db_name passed when
   // opening the DB.
   // Default: empty
-  std::vector<std::string> db_paths;
+  std::vector<DbPath> db_paths;
 
   // This specifies the info LOG dir.
   // If it is empty, the log files will be in the same dir as data.

util/ldb_cmd.cc

@@ -18,6 +18,7 @@
 
 #include <ctime>
 #include <dirent.h>
+#include <limits>
 #include <sstream>
 #include <string>
 #include <stdexcept>
@@ -287,7 +288,7 @@ Options LDBCommand::PrepareOptionsForOpenDB() {
   }
 
   if (opt.db_paths.size() == 0) {
-    opt.db_paths.push_back(db_path_);
+    opt.db_paths.emplace_back(db_path_, std::numeric_limits<uint64_t>::max());
   }
 
   return opt;