fast look up purge_queue (#5796)

Summary:
purge_queue_ maybe contains thousands sst files, for example manual compact a range. If full scan is triggered at the same time and the total sst files number is large, RocksDB will be blocked at https://github.com/facebook/rocksdb/blob/master/db/db_impl_files.cc#L150 for several seconds. In our environment we have 140,000 sst files and the manual compaction delete about 1000 sst files, it blocked about 2 minutes.

Commandeering https://github.com/facebook/rocksdb/issues/5290.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5796

Differential Revision: D17357775

Pulled By: riversand963

fbshipit-source-id: 20eacca917355b8de975ccc7b1c9a3e7bd5b201a

db/db_impl/db_impl.cc

@@ -1314,32 +1314,28 @@ void DBImpl::SchedulePurge() {
 void DBImpl::BackgroundCallPurge() {
   mutex_.Lock();
 
-  // We use one single loop to clear both queues so that after existing the loop
+  while (!logs_to_free_queue_.empty()) {
-  // both queues are empty. This is stricter than what is needed, but can make
+    assert(!logs_to_free_queue_.empty());
-  // it easier for us to reason the correctness.
+    log::Writer* log_writer = *(logs_to_free_queue_.begin());
-  while (!purge_queue_.empty() || !logs_to_free_queue_.empty()) {
+    logs_to_free_queue_.pop_front();
-    // Check logs_to_free_queue_ first and close log writers.
+    mutex_.Unlock();
-    if (!logs_to_free_queue_.empty()) {
+    delete log_writer;
-      assert(!logs_to_free_queue_.empty());
+    mutex_.Lock();
-      log::Writer* log_writer = *(logs_to_free_queue_.begin());
-      logs_to_free_queue_.pop_front();
-      mutex_.Unlock();
-      delete log_writer;
-      mutex_.Lock();
-    } else {
-      auto purge_file = purge_queue_.begin();
-      auto fname = purge_file->fname;
-      auto dir_to_sync = purge_file->dir_to_sync;
-      auto type = purge_file->type;
-      auto number = purge_file->number;
-      auto job_id = purge_file->job_id;
-      purge_queue_.pop_front();
-
-      mutex_.Unlock();
-      DeleteObsoleteFileImpl(job_id, fname, dir_to_sync, type, number);
-      mutex_.Lock();
-    }
   }
+  for (const auto& file : purge_files_) {
+    const PurgeFileInfo& purge_file = file.second;
+    const std::string& fname = purge_file.fname;
+    const std::string& dir_to_sync = purge_file.dir_to_sync;
+    FileType type = purge_file.type;
+    uint64_t number = purge_file.number;
+    int job_id = purge_file.job_id;
+
+    mutex_.Unlock();
+    DeleteObsoleteFileImpl(job_id, fname, dir_to_sync, type, number);
+    mutex_.Lock();
+  }
+  purge_files_.clear();
+
   bg_purge_scheduled_--;
 
   bg_cv_.SignalAll();

db/db_impl/db_impl.h

@@ -347,7 +347,8 @@ class DBImpl : public DB {
                               uint64_t* manifest_file_size,
                               bool flush_memtable = true) override;
   virtual Status GetSortedWalFiles(VectorLogPtr& files) override;
-  virtual Status GetCurrentWalFile(std::unique_ptr<LogFile>* current_log_file) override;
+  virtual Status GetCurrentWalFile(
+      std::unique_ptr<LogFile>* current_log_file) override;
 
   virtual Status GetUpdatesSince(
       SequenceNumber seq_number, std::unique_ptr<TransactionLogIterator>* iter,
@@ -1784,12 +1785,12 @@ class DBImpl : public DB {
   // ColumnFamilyData::pending_compaction_ == true)
   std::deque<ColumnFamilyData*> compaction_queue_;
 
-  // A queue to store filenames of the files to be purged
+  // A map to store file numbers and filenames of the files to be purged
-  std::deque<PurgeFileInfo> purge_queue_;
+  std::unordered_map<uint64_t, PurgeFileInfo> purge_files_;
 
   // A vector to store the file numbers that have been assigned to certain
   // JobContext. Current implementation tracks ssts only.
-  std::vector<uint64_t> files_grabbed_for_purge_;
+  std::unordered_set<uint64_t> files_grabbed_for_purge_;
 
   // A queue to store log writers to close
   std::deque<log::Writer*> logs_to_free_queue_;

db/db_impl/db_impl_compaction_flush.cc

@@ -2090,7 +2090,7 @@ void DBImpl::SchedulePendingPurge(std::string fname, std::string dir_to_sync,
                                   FileType type, uint64_t number, int job_id) {
   mutex_.AssertHeld();
   PurgeFileInfo file_info(fname, dir_to_sync, type, number, job_id);
-  purge_queue_.push_back(std::move(file_info));
+  purge_files_.insert({{number, std::move(file_info)}});
 }
 
 void DBImpl::BGWorkFlush(void* arg) {
@@ -3077,34 +3077,20 @@ void DBImpl::InstallSuperVersionAndScheduleWork(
 }
 
 // ShouldPurge is called by FindObsoleteFiles when doing a full scan,
-// and db mutex (mutex_) should already be held. This function performs a
+// and db mutex (mutex_) should already be held.
-// linear scan of an vector (files_grabbed_for_purge_) in search of a
-// certain element. We expect FindObsoleteFiles with full scan to occur once
-// every 10 hours by default, and the size of the vector is small.
-// Therefore, the cost is affordable even if the mutex is held.
 // Actually, the current implementation of FindObsoleteFiles with
 // full_scan=true can issue I/O requests to obtain list of files in
 // directories, e.g. env_->getChildren while holding db mutex.
-// In the future, if we want to reduce the cost of search, we may try to keep
-// the vector sorted.
 bool DBImpl::ShouldPurge(uint64_t file_number) const {
-  for (auto fn : files_grabbed_for_purge_) {
+  return files_grabbed_for_purge_.find(file_number) ==
-    if (file_number == fn) {
+             files_grabbed_for_purge_.end() &&
-      return false;
+         purge_files_.find(file_number) == purge_files_.end();
-    }
-  }
-  for (const auto& purge_file_info : purge_queue_) {
-    if (purge_file_info.number == file_number) {
-      return false;
-    }
-  }
-  return true;
 }
 
 // MarkAsGrabbedForPurge is called by FindObsoleteFiles, and db mutex
 // (mutex_) should already be held.
 void DBImpl::MarkAsGrabbedForPurge(uint64_t file_number) {
-  files_grabbed_for_purge_.emplace_back(file_number);
+  files_grabbed_for_purge_.insert(file_number);
 }
 
 void DBImpl::SetSnapshotChecker(SnapshotChecker* snapshot_checker) {

db/db_impl/db_impl_files.cc

@@ -15,6 +15,7 @@
 #include "db/memtable_list.h"
 #include "file/file_util.h"
 #include "file/sst_file_manager_impl.h"
+#include "util/autovector.h"
 
 namespace rocksdb {
 
@@ -495,13 +496,15 @@ void DBImpl::PurgeObsoleteFiles(JobContext& state, bool schedule_only) {
     // After purging obsolete files, remove them from files_grabbed_for_purge_.
     // Use a temporary vector to perform bulk deletion via swap.
     InstrumentedMutexLock guard_lock(&mutex_);
-    std::vector<uint64_t> tmp;
+    autovector<uint64_t> to_be_removed;
     for (auto fn : files_grabbed_for_purge_) {
-      if (files_to_del.count(fn) == 0) {
+      if (files_to_del.count(fn) != 0) {
-        tmp.emplace_back(fn);
+        to_be_removed.emplace_back(fn);
       }
     }
-    files_grabbed_for_purge_.swap(tmp);
+    for (auto fn : to_be_removed) {
+      files_grabbed_for_purge_.erase(fn);
+    }
   }
 
   // Delete old info log files.

db/obsolete_files_test.cc

@@ -171,8 +171,8 @@ TEST_F(ObsoleteFilesTest, RaceForObsoleteFileDeletion) {
       });
   SyncPoint::GetInstance()->SetCallBack(
       "DBImpl::CloseHelper:PendingPurgeFinished", [&](void* arg) {
-        std::vector<uint64_t>* files_grabbed_for_purge_ptr =
+        std::unordered_set<uint64_t>* files_grabbed_for_purge_ptr =
-            reinterpret_cast<std::vector<uint64_t>*>(arg);
+            reinterpret_cast<std::unordered_set<uint64_t>*>(arg);
         ASSERT_TRUE(files_grabbed_for_purge_ptr->empty());
       });
   SyncPoint::GetInstance()->EnableProcessing();