Check stop level trigger-0 before slowdown level-0 trigger

Summary: ...

Test Plan: Can't repro the test failure, but let's see what jenkins says

Reviewers: zagfox, sdong, ljin

Reviewed By: sdong, ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D23061

db/column_family.cc

@@ -326,6 +326,13 @@ void ColumnFamilyData::RecalculateWriteStallConditions() {
           "[%s] Stopping writes because we have %d immutable memtables "
           "(waiting for flush)",
           name_.c_str(), imm()->size());
+    } else if (current_->NumLevelFiles(0) >=
+               options_.level0_stop_writes_trigger) {
+      write_controller_token_ = write_controller->GetStopToken();
+      internal_stats_->AddCFStats(InternalStats::LEVEL0_NUM_FILES, 1);
+      Log(options_.info_log,
+          "[%s] Stopping writes because we have %d level-0 files",
+          name_.c_str(), current_->NumLevelFiles(0));
     } else if (options_.level0_slowdown_writes_trigger >= 0 &&
                current_->NumLevelFiles(0) >=
                    options_.level0_slowdown_writes_trigger) {
@@ -338,13 +345,6 @@ void ColumnFamilyData::RecalculateWriteStallConditions() {
           "[%s] Stalling writes because we have %d level-0 files (%" PRIu64
           "us)",
           name_.c_str(), current_->NumLevelFiles(0), slowdown);
-    } else if (current_->NumLevelFiles(0) >=
-               options_.level0_stop_writes_trigger) {
-      write_controller_token_ = write_controller->GetStopToken();
-      internal_stats_->AddCFStats(InternalStats::LEVEL0_NUM_FILES, 1);
-      Log(options_.info_log,
-          "[%s] Stopping writes because we have %d level-0 files",
-          name_.c_str(), current_->NumLevelFiles(0));
     } else if (options_.hard_rate_limit > 1.0 &&
                score > options_.hard_rate_limit) {
       uint64_t kHardLimitSlowdown = 1000;

db/db_test.cc

@@ -7827,6 +7827,26 @@ TEST(DBTest, MTRandomTimeoutTest) {
   }
 }
 
+TEST(DBTest, Level0StopWritesTest) {
+  Options options = CurrentOptions();
+  options.level0_slowdown_writes_trigger = 2;
+  options.level0_stop_writes_trigger = 4;
+  options.disable_auto_compactions = 4;
+  options.max_mem_compaction_level = 0;
+  Reopen(&options);
+
+  // create 4 level0 tables
+  for (int i = 0; i < 4; ++i) {
+    Put("a", "b");
+    Flush();
+  }
+
+  WriteOptions woptions;
+  woptions.timeout_hint_us = 30 * 1000;  // 30 ms
+  Status s = Put("a", "b", woptions);
+  ASSERT_TRUE(s.IsTimedOut());
+}
+
 }  // anonymous namespace
 
 /*