Use Microseconds for decoding time (facebookincubator#8589)

Summary:
Pull Request resolved: facebookincubator#8589

The decoding times are in the single digits ms most of the times, even 1 ms is normal. So let's give it more resolution than 1 ms.

Reviewed By: helfman

Differential Revision: D53200548

fbshipit-source-id: 8154a80e4a4163c51c3efece792d64df3048fb03

velox/dwio/common/Options.h

@@ -131,7 +131,7 @@ class RowReaderOptions {
   // (in dwrf row reader). todo: encapsulate this and keySelectionCallBack_ in a
   // struct
   std::function<void(uint64_t)> blockedOnIoCallback_;
-  std::function<void(uint64_t)> decodingTimeMsCallback_;
+  std::function<void(uint64_t)> decodingTimeUsCallback_;
   std::function<void(uint16_t)> stripeCountCallback_;
   bool eagerFirstStripeLoad = true;
   uint64_t skipRows_ = 0;
@@ -350,12 +350,12 @@ class RowReaderOptions {
     return blockedOnIoCallback_;
   }
 
-  void setDecodingTimeMsCallback(std::function<void(int64_t)> decodingTimeMs) {
-    decodingTimeMsCallback_ = std::move(decodingTimeMs);
+  void setDecodingTimeUsCallback(std::function<void(int64_t)> decodingTimeUs) {
+    decodingTimeUsCallback_ = std::move(decodingTimeUs);
   }
 
-  std::function<void(int64_t)> getDecodingTimeMsCallback() const {
-    return decodingTimeMsCallback_;
+  std::function<void(int64_t)> getDecodingTimeUsCallback() const {
+    return decodingTimeUsCallback_;
   }
 
   void setStripeCountCallback(

velox/dwio/dwrf/reader/DwrfReader.cpp

@@ -15,6 +15,9 @@
  */
 
 #include "velox/dwio/dwrf/reader/DwrfReader.h"
+
+#include <chrono>
+
 #include "velox/dwio/common/TypeUtils.h"
 #include "velox/dwio/common/exception/Exception.h"
 #include "velox/dwio/dwrf/reader/ColumnReader.h"
@@ -35,7 +38,7 @@ DwrfRowReader::DwrfRowReader(
     : StripeReaderBase(reader),
       options_(opts),
       executor_{options_.getDecodingExecutor()},
-      decodingTimeMsCallback_{options_.getDecodingTimeMsCallback()},
+      decodingTimeUsCallback_{options_.getDecodingTimeUsCallback()},
       stripeCountCallback_{options_.getStripeCountCallback()},
       columnSelector_{std::make_shared<ColumnSelector>(
           ColumnSelector::apply(opts.getSelector(), reader->getSchema()))} {
@@ -274,17 +277,23 @@ void DwrfRowReader::readNext(
     const dwio::common::Mutation* mutation,
     VectorPtr& result) {
   if (!selectiveColumnReader_) {
-    const auto startTime = std::chrono::high_resolution_clock::now();
+    std::optional<std::chrono::steady_clock::time_point> startTime;
+    if (decodingTimeUsCallback_) {
+      // We'll use wall time since we have parallel decoding.
+      // If we move to sequential decoding only, we can use CPU time.
+      startTime.emplace(std::chrono::steady_clock::now());
+    }
     // TODO: Move row number appending logic here.  Currently this is done in
     // the wrapper reader.
     VELOX_CHECK(
         mutation == nullptr,
         "Mutation pushdown is only supported in selective reader");
     columnReader_->next(rowsToRead, result);
-    if (decodingTimeMsCallback_) {
-      auto decodingTime = std::chrono::duration_cast<std::chrono::milliseconds>(
-          std::chrono::high_resolution_clock::now() - startTime);
-      decodingTimeMsCallback_(decodingTime.count());
+    if (startTime.has_value()) {
+      decodingTimeUsCallback_(
+          std::chrono::duration_cast<std::chrono::microseconds>(
+              std::chrono::steady_clock::now() - startTime.value())
+              .count());
     }
     return;
   }

velox/dwio/dwrf/reader/DwrfReader.h

@@ -149,7 +149,7 @@ class DwrfRowReader : public StrideIndexProvider,
   std::shared_ptr<StripeDictionaryCache> stripeDictionaryCache_;
   dwio::common::RowReaderOptions options_;
   std::shared_ptr<folly::Executor> executor_;
-  std::function<void(uint64_t)> decodingTimeMsCallback_;
+  std::function<void(uint64_t)> decodingTimeUsCallback_;
   std::function<void(uint16_t)> stripeCountCallback_;
 
   struct PrefetchedStripeState {