CompactRange() to use bottom pool when goes to bottommost level (#6593)

Summary:
In automatic compaction, if a compaction is bottommost, it goes to bottom thread pool. We should do the same for manual compaction too.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6593

Test Plan: Add a unit test. See all existing tests pass.

Reviewed By: ajkr

Differential Revision: D20637408

fbshipit-source-id: cb03031e8f895085f7acf6d2d65e69e84c9ddef3

db/db_compaction_test.cc

@@ -593,6 +593,72 @@ TEST_P(DBCompactionTestWithParam, CompactionDeletionTriggerReopen) {
   }
 }
 
+TEST_F(DBCompactionTest, CompactRangeBottomPri) {
+  ASSERT_OK(Put(Key(50), ""));
+  ASSERT_OK(Flush());
+  ASSERT_OK(Put(Key(100), ""));
+  ASSERT_OK(Flush());
+  ASSERT_OK(Put(Key(200), ""));
+  ASSERT_OK(Flush());
+
+  {
+    CompactRangeOptions cro;
+    cro.change_level = true;
+    cro.target_level = 2;
+    dbfull()->CompactRange(cro, nullptr, nullptr);
+  }
+  ASSERT_EQ("0,0,3", FilesPerLevel(0));
+
+  ASSERT_OK(Put(Key(1), ""));
+  ASSERT_OK(Put(Key(199), ""));
+  ASSERT_OK(Flush());
+  ASSERT_OK(Put(Key(2), ""));
+  ASSERT_OK(Put(Key(199), ""));
+  ASSERT_OK(Flush());
+  ASSERT_EQ("2,0,3", FilesPerLevel(0));
+
+  // Now we have 2 L0 files, and 3 L2 files, and a manual compaction will
+  // be triggered.
+  // Two compaction jobs will run. One compacts 2 L0 files in Low Pri Pool
+  // and one compact to L2 in bottom pri pool.
+  int low_pri_count = 0;
+  int bottom_pri_count = 0;
+  SyncPoint::GetInstance()->SetCallBack(
+      "ThreadPoolImpl::Impl::BGThread:BeforeRun", [&](void* arg) {
+        Env::Priority* pri = reinterpret_cast<Env::Priority*>(arg);
+        // First time is low pri pool in the test case.
+        if (low_pri_count == 0 && bottom_pri_count == 0) {
+          ASSERT_EQ(Env::Priority::LOW, *pri);
+        }
+        if (*pri == Env::Priority::LOW) {
+          low_pri_count++;
+        } else {
+          bottom_pri_count++;
+        }
+      });
+  SyncPoint::GetInstance()->EnableProcessing();
+  env_->SetBackgroundThreads(1, Env::Priority::BOTTOM);
+  dbfull()->CompactRange(CompactRangeOptions(), nullptr, nullptr);
+  ASSERT_EQ(1, low_pri_count);
+  ASSERT_EQ(1, bottom_pri_count);
+  ASSERT_EQ("0,0,2", FilesPerLevel(0));
+
+  // Recompact bottom most level uses bottom pool
+  CompactRangeOptions cro;
+  cro.bottommost_level_compaction = BottommostLevelCompaction::kForce;
+  dbfull()->CompactRange(cro, nullptr, nullptr);
+  ASSERT_EQ(1, low_pri_count);
+  ASSERT_EQ(2, bottom_pri_count);
+
+  env_->SetBackgroundThreads(0, Env::Priority::BOTTOM);
+  dbfull()->CompactRange(cro, nullptr, nullptr);
+  // Low pri pool is used if bottom pool has size 0.
+  ASSERT_EQ(2, low_pri_count);
+  ASSERT_EQ(2, bottom_pri_count);
+
+  SyncPoint::GetInstance()->DisableProcessing();
+}
+
 TEST_F(DBCompactionTest, DisableStatsUpdateReopen) {
   uint64_t db_size[3];
   for (int test = 0; test < 2; ++test) {

db/db_impl/db_impl_compaction_flush.cc

@@ -1510,7 +1510,12 @@ Status DBImpl::RunManualCompaction(
       }
       manual.incomplete = false;
       bg_compaction_scheduled_++;
-      env_->Schedule(&DBImpl::BGWorkCompaction, ca, Env::Priority::LOW, this,
+      Env::Priority thread_pool_pri = Env::Priority::LOW;
+      if (compaction->bottommost_level() &&
+          env_->GetBackgroundThreads(Env::Priority::BOTTOM) > 0) {
+        thread_pool_pri = Env::Priority::BOTTOM;
+      }
+      env_->Schedule(&DBImpl::BGWorkCompaction, ca, thread_pool_pri, this,
                      &DBImpl::UnscheduleCompactionCallback);
       scheduled = true;
     }

util/threadpool_imp.cc

@@ -9,9 +9,6 @@
 
 #include "util/threadpool_imp.h"
 
-#include "monitoring/thread_status_util.h"
-#include "port/port.h"
-
 #ifndef OS_WIN
 #  include <unistd.h>
 #endif
@@ -31,6 +28,10 @@
 #include <thread>
 #include <vector>
 
+#include "monitoring/thread_status_util.h"
+#include "port/port.h"
+#include "test_util/sync_point.h"
+
 namespace ROCKSDB_NAMESPACE {
 
 void ThreadPoolImpl::PthreadCall(const char* label, int result) {
@@ -262,6 +263,10 @@ void ThreadPoolImpl::Impl::BGThread(size_t thread_id) {
     (void)decrease_io_priority;  // avoid 'unused variable' error
     (void)decrease_cpu_priority;
 #endif
+
+    TEST_SYNC_POINT_CALLBACK("ThreadPoolImpl::Impl::BGThread:BeforeRun",
+                             &priority_);
+
     func();
   }
 }