Allow DB reopen with reduced options.num_levels

Summary:
Allow user to reduce number of levels in LSM by issue a full CompactRange() and put the result in a lower level, and then reopen DB with reduced options.num_levels. Previous this will fail on reopen on when recovery replaying the previous MANIFEST and found a historical file was on a higher level than the new options.num_levels. The workaround was after CompactRange(), reopen the DB with old num_levels, which will create a new MANIFEST, and then reopen the DB again with new num_levels.

This patch relax the check of levels during recovery. It allows DB to open if there was a historical file on level > options.num_levels, but was also deleted.
Closes https://github.com/facebook/rocksdb/pull/2740

Differential Revision: D5629354

Pulled By: yiwu-arbug

fbshipit-source-id: 545903f6b36b6083e8cbaf777176aef2f488021d

db/db_test2.cc

@@ -2304,6 +2304,27 @@ TEST_F(DBTest2, RateLimitedCompactionReads) {
   }
 }
 #endif  // ROCKSDB_LITE
+
+// Make sure DB can be reopen with reduced number of levels, given no file
+// is on levels higher than the new num_levels.
+TEST_F(DBTest2, ReduceLevel) {
+  Options options;
+  options.disable_auto_compactions = true;
+  options.num_levels = 7;
+  Reopen(options);
+  Put("foo", "bar");
+  Flush();
+  MoveFilesToLevel(6);
+  ASSERT_EQ("0,0,0,0,0,0,1", FilesPerLevel());
+  CompactRangeOptions compact_options;
+  compact_options.change_level = true;
+  compact_options.target_level = 1;
+  dbfull()->CompactRange(compact_options, nullptr, nullptr);
+  ASSERT_EQ("0,1", FilesPerLevel());
+  options.num_levels = 3;
+  Reopen(options);
+  ASSERT_EQ("0,1", FilesPerLevel());
+}
 }  // namespace rocksdb
 
 int main(int argc, char** argv) {

db/version_builder.cc

@@ -17,6 +17,7 @@
 #include <algorithm>
 #include <atomic>
 #include <functional>
+#include <map>
 #include <set>
 #include <thread>
 #include <unordered_map>
@@ -87,7 +88,16 @@ class VersionBuilder::Rep {
   Logger* info_log_;
   TableCache* table_cache_;
   VersionStorageInfo* base_vstorage_;
+  int num_levels_;
   LevelState* levels_;
+  // Store states of levels larger than num_levels_. We do this instead of
+  // storing them in levels_ to avoid regression in case there are no files
+  // on invalid levels. The version is not consistent if in the end the files
+  // on invalid levels don't cancel out.
+  std::map<int, std::unordered_set<uint64_t>> invalid_levels_;
+  // Whether there are invalid new files or invalid deletion on levels larger
+  // than num_levels_.
+  bool has_invalid_levels_;
   FileComparator level_zero_cmp_;
   FileComparator level_nonzero_cmp_;
 
@@ -97,8 +107,10 @@ class VersionBuilder::Rep {
       : env_options_(env_options),
         info_log_(info_log),
         table_cache_(table_cache),
-        base_vstorage_(base_vstorage) {
-    levels_ = new LevelState[base_vstorage_->num_levels()];
+        base_vstorage_(base_vstorage),
+        num_levels_(base_vstorage->num_levels()),
+        has_invalid_levels_(false) {
+    levels_ = new LevelState[num_levels_];
     level_zero_cmp_.sort_method = FileComparator::kLevel0;
     level_nonzero_cmp_.sort_method = FileComparator::kLevelNon0;
     level_nonzero_cmp_.internal_comparator =
@@ -106,7 +118,7 @@ class VersionBuilder::Rep {
   }
 
   ~Rep() {
-    for (int level = 0; level < base_vstorage_->num_levels(); level++) {
+    for (int level = 0; level < num_levels_; level++) {
       const auto& added = levels_[level].added_files;
       for (auto& pair : added) {
         UnrefFile(pair.second);
@@ -137,7 +149,7 @@ class VersionBuilder::Rep {
     }
 #endif
     // make sure the files are sorted correctly
-    for (int level = 0; level < vstorage->num_levels(); level++) {
+    for (int level = 0; level < num_levels_; level++) {
       auto& level_files = vstorage->LevelFiles(level);
       for (size_t i = 1; i < level_files.size(); i++) {
         auto f1 = level_files[i - 1];
@@ -196,7 +208,7 @@ class VersionBuilder::Rep {
 #endif
     // a file to be deleted better exist in the previous version
     bool found = false;
-    for (int l = 0; !found && l < base_vstorage_->num_levels(); l++) {
+    for (int l = 0; !found && l < num_levels_; l++) {
       const std::vector<FileMetaData*>& base_files =
           base_vstorage_->LevelFiles(l);
       for (size_t i = 0; i < base_files.size(); i++) {
@@ -210,7 +222,7 @@ class VersionBuilder::Rep {
     // if the file did not exist in the previous version, then it
     // is possibly moved from lower level to higher level in current
     // version
-    for (int l = level + 1; !found && l < base_vstorage_->num_levels(); l++) {
+    for (int l = level + 1; !found && l < num_levels_; l++) {
       auto& level_added = levels_[l].added_files;
       auto got = level_added.find(number);
       if (got != level_added.end()) {
@@ -233,6 +245,19 @@ class VersionBuilder::Rep {
     }
   }
 
+  bool CheckConsistencyForNumLevels() {
+    // Make sure there are no files on or beyond num_levels().
+    if (has_invalid_levels_) {
+      return false;
+    }
+    for (auto& level : invalid_levels_) {
+      if (level.second.size() > 0) {
+        return false;
+      }
+    }
+    return true;
+  }
+
   // Apply all of the edits in *edit to the current state.
   void Apply(VersionEdit* edit) {
     CheckConsistency(base_vstorage_);
@@ -242,6 +267,7 @@ class VersionBuilder::Rep {
     for (const auto& del_file : del) {
       const auto level = del_file.first;
       const auto number = del_file.second;
+      if (level < num_levels_) {
         levels_[level].deleted_files.insert(number);
         CheckConsistencyForDeletes(edit, number, level);
 
@@ -250,11 +276,20 @@ class VersionBuilder::Rep {
           UnrefFile(exising->second);
           levels_[level].added_files.erase(number);
         }
+      } else {
+        if (invalid_levels_[level].count(number) > 0) {
+          invalid_levels_[level].erase(number);
+        } else {
+          // Deleting an non-existing file on invalid level.
+          has_invalid_levels_ = true;
+        }
+      }
     }
 
     // Add new files
     for (const auto& new_file : edit->GetNewFiles()) {
       const int level = new_file.first;
+      if (level < num_levels_) {
         FileMetaData* f = new FileMetaData(new_file.second);
         f->refs = 1;
 
@@ -262,6 +297,15 @@ class VersionBuilder::Rep {
                levels_[level].added_files.end());
         levels_[level].deleted_files.erase(f->fd.GetNumber());
         levels_[level].added_files[f->fd.GetNumber()] = f;
+      } else {
+        uint64_t number = new_file.second.fd.GetNumber();
+        if (invalid_levels_[level].count(number) == 0) {
+          invalid_levels_[level].insert(number);
+        } else {
+          // Creating an already existing file on invalid level.
+          has_invalid_levels_ = true;
+        }
+      }
     }
   }
 
@@ -270,7 +314,7 @@ class VersionBuilder::Rep {
     CheckConsistency(base_vstorage_);
     CheckConsistency(vstorage);
 
-    for (int level = 0; level < base_vstorage_->num_levels(); level++) {
+    for (int level = 0; level < num_levels_; level++) {
       const auto& cmp = (level == 0) ? level_zero_cmp_ : level_nonzero_cmp_;
       // Merge the set of added files with the set of pre-existing files.
       // Drop any deleted files.  Store the result in *v.
@@ -325,7 +369,7 @@ class VersionBuilder::Rep {
     assert(table_cache_ != nullptr);
     // <file metadata, level>
     std::vector<std::pair<FileMetaData*, int>> files_meta;
-    for (int level = 0; level < base_vstorage_->num_levels(); level++) {
+    for (int level = 0; level < num_levels_; level++) {
       for (auto& file_meta_pair : levels_[level].added_files) {
         auto* file_meta = file_meta_pair.second;
         assert(!file_meta->table_reader_handle);
@@ -386,24 +430,35 @@ VersionBuilder::VersionBuilder(const EnvOptions& env_options,
                                VersionStorageInfo* base_vstorage,
                                Logger* info_log)
     : rep_(new Rep(env_options, info_log, table_cache, base_vstorage)) {}
+
 VersionBuilder::~VersionBuilder() { delete rep_; }
+
 void VersionBuilder::CheckConsistency(VersionStorageInfo* vstorage) {
   rep_->CheckConsistency(vstorage);
 }
+
 void VersionBuilder::CheckConsistencyForDeletes(VersionEdit* edit,
                                                 uint64_t number, int level) {
   rep_->CheckConsistencyForDeletes(edit, number, level);
 }
+
+bool VersionBuilder::CheckConsistencyForNumLevels() {
+  return rep_->CheckConsistencyForNumLevels();
+}
+
 void VersionBuilder::Apply(VersionEdit* edit) { rep_->Apply(edit); }
+
 void VersionBuilder::SaveTo(VersionStorageInfo* vstorage) {
   rep_->SaveTo(vstorage);
 }
+
 void VersionBuilder::LoadTableHandlers(
     InternalStats* internal_stats, int max_threads,
     bool prefetch_index_and_filter_in_cache) {
   rep_->LoadTableHandlers(internal_stats, max_threads,
                           prefetch_index_and_filter_in_cache);
 }
+
 void VersionBuilder::MaybeAddFile(VersionStorageInfo* vstorage, int level,
                                   FileMetaData* f) {
   rep_->MaybeAddFile(vstorage, level, f);

db/version_builder.h

@@ -29,6 +29,7 @@ class VersionBuilder {
   void CheckConsistency(VersionStorageInfo* vstorage);
   void CheckConsistencyForDeletes(VersionEdit* edit, uint64_t number,
                                   int level);
+  bool CheckConsistencyForNumLevels();
   void Apply(VersionEdit* edit);
   void SaveTo(VersionStorageInfo* vstorage);
   void LoadTableHandlers(InternalStats* internal_stats, int max_threads,

db/version_set.cc

@@ -2842,11 +2842,6 @@ Status VersionSet::Recover(
         cfd = column_family_set_->GetColumnFamily(edit.column_family_);
         // this should never happen since cf_in_builders is true
         assert(cfd != nullptr);
-        if (edit.max_level_ >= cfd->current()->storage_info()->num_levels()) {
-          s = Status::InvalidArgument(
-              "db has more levels than options.num_levels");
-          break;
-        }
 
         // if it is not column family add or column family drop,
         // then it's a file add/delete, which should be forwarded
@@ -2930,6 +2925,18 @@ Status VersionSet::Recover(
         list_of_not_found);
   }
 
+  if (s.ok()) {
+    for (auto cfd : *column_family_set_) {
+      assert(builders.count(cfd->GetID()) > 0);
+      auto* builder = builders[cfd->GetID()]->version_builder();
+      if (!builder->CheckConsistencyForNumLevels()) {
+        s = Status::InvalidArgument(
+            "db has more levels than options.num_levels");
+        break;
+      }
+    }
+  }
+
   if (s.ok()) {
     for (auto cfd : *column_family_set_) {
       if (cfd->IsDropped()) {