Fix an issue of manual / auto compaction data race

Summary:
A data race between a manual and an auto compaction can cause a scheduled automatic compaction to be cancelled and never rescheduled again. This may cause a condition of hanging forever. Fix this by always making sure the cancelled compaction is put back to the compaction queue.
Closes https://github.com/facebook/rocksdb/pull/2238

Differential Revision: D4984591

Pulled By: siying

fbshipit-source-id: 3ab153886403c7b991896dcb2158b96cac12f227

db/db_compaction_test.cc

@@ -1852,6 +1852,47 @@ TEST_F(DBCompactionTest, L0_CompactionBug_Issue44_b) {
   } while (ChangeCompactOptions());
 }
 
+TEST_F(DBCompactionTest, ManualAutoRace) {
+  CreateAndReopenWithCF({"pikachu"}, CurrentOptions());
+  rocksdb::SyncPoint::GetInstance()->LoadDependency(
+      {{"DBImpl::BGWorkCompaction", "DBCompactionTest::ManualAutoRace:1"},
+       {"DBImpl::RunManualCompaction:WaitScheduled",
+        "BackgroundCallCompaction:0"}});
+
+  rocksdb::SyncPoint::GetInstance()->EnableProcessing();
+
+  Put(1, "foo", "");
+  Put(1, "bar", "");
+  Flush(1);
+  Put(1, "foo", "");
+  Put(1, "bar", "");
+  // Generate four files in CF 0, which should trigger an auto compaction
+  Put("foo", "");
+  Put("bar", "");
+  Flush();
+  Put("foo", "");
+  Put("bar", "");
+  Flush();
+  Put("foo", "");
+  Put("bar", "");
+  Flush();
+  Put("foo", "");
+  Put("bar", "");
+  Flush();
+
+  // The auto compaction is scheduled but waited until here
+  TEST_SYNC_POINT("DBCompactionTest::ManualAutoRace:1");
+  // The auto compaction will wait until the the manual compaction is registerd
+  // before processing so that it will be cancelled.
+  dbfull()->CompactRange(CompactRangeOptions(), handles_[1], nullptr, nullptr);
+  ASSERT_EQ("0,1", FilesPerLevel(1));
+
+  // Eventually the cancelled compaction will be rescheduled and executed.
+  dbfull()->TEST_WaitForCompact();
+  ASSERT_EQ("0,1", FilesPerLevel(0));
+  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
+}
+
 TEST_P(DBCompactionTestWithParam, ManualCompaction) {
   Options options = CurrentOptions();
   options.max_subcompactions = max_subcompactions_;

db/db_impl_compaction_flush.cc

@@ -828,6 +828,7 @@ Status DBImpl::RunManualCompaction(ColumnFamilyData* cfd, int input_level,
   TEST_SYNC_POINT_CALLBACK("DBImpl::RunManualCompaction:NotScheduled", &mutex_);
   if (exclusive) {
     while (bg_compaction_scheduled_ > 0) {
+      TEST_SYNC_POINT("DBImpl::RunManualCompaction:WaitScheduled");
       ROCKS_LOG_INFO(
           immutable_db_options_.info_log,
           "[%s] Manual compaction waiting for all other scheduled background "
@@ -1394,6 +1395,16 @@ Status DBImpl::BackgroundCompaction(bool* made_progress,
                : m->manual_end->DebugString().c_str()));
     }
   } else if (!compaction_queue_.empty()) {
+    if (HaveManualCompaction(compaction_queue_.front())) {
+      // Can't compact right now, but try again later
+      TEST_SYNC_POINT("DBImpl::BackgroundCompaction()::Conflict");
+
+      // Stay in the compaciton queue.
+      unscheduled_compactions_++;
+
+      return Status::OK();
+    }
+
     // cfd is referenced here
     auto cfd = PopFirstFromCompactionQueue();
     // We unreference here because the following code will take a Ref() on
@@ -1408,12 +1419,6 @@ Status DBImpl::BackgroundCompaction(bool* made_progress,
       return Status::OK();
     }
 
-    if (HaveManualCompaction(cfd)) {
-      // Can't compact right now, but try again later
-      TEST_SYNC_POINT("DBImpl::BackgroundCompaction()::Conflict");
-      return Status::OK();
-    }
-
     // Pick up latest mutable CF Options and use it throughout the
     // compaction job
     // Compaction makes a copy of the latest MutableCFOptions. It should be used