perf_context measure user bytes read

Summary:
With this PR, we can measure read-amp for queries where perf_context is enabled as follows:

```
SetPerfLevel(kEnableCount);
Get(1, "foo");
double read_amp = static_cast<double>(get_perf_context()->block_read_byte / get_perf_context()->get_read_bytes);
SetPerfLevel(kDisable);
```

Our internal infra enables perf_context for a sampling of queries. So we'll be able to compute the read-amp for the sample set, which can give us a good estimate of read-amp.
Closes https://github.com/facebook/rocksdb/pull/2749

Differential Revision: D5647240

Pulled By: ajkr

fbshipit-source-id: ad73550b06990cf040cc4528fa885360f308ec12

db/db_basic_test.cc

@@ -360,7 +360,6 @@ TEST_F(DBBasicTest, FLUSH) {
     WriteOptions writeOpt = WriteOptions();
     writeOpt.disableWAL = true;
     SetPerfLevel(kEnableTime);
-    ;
     ASSERT_OK(dbfull()->Put(writeOpt, handles_[1], "foo", "v1"));
     // this will now also flush the last 2 writes
     ASSERT_OK(Flush(1));
@@ -369,6 +368,7 @@ TEST_F(DBBasicTest, FLUSH) {
     get_perf_context()->Reset();
     Get(1, "foo");
     ASSERT_TRUE((int)get_perf_context()->get_from_output_files_time > 0);
+    ASSERT_EQ(2, (int)get_perf_context()->get_read_bytes);
 
     ReopenWithColumnFamilies({"default", "pikachu"}, CurrentOptions());
     ASSERT_EQ("v1", Get(1, "foo"));
@@ -725,6 +725,7 @@ TEST_F(DBBasicTest, FlushOneColumnFamily) {
 TEST_F(DBBasicTest, MultiGetSimple) {
   do {
     CreateAndReopenWithCF({"pikachu"}, CurrentOptions());
+    SetPerfLevel(kEnableCount);
     ASSERT_OK(Put(1, "k1", "v1"));
     ASSERT_OK(Put(1, "k2", "v2"));
     ASSERT_OK(Put(1, "k3", "v3"));
@@ -738,12 +739,15 @@ TEST_F(DBBasicTest, MultiGetSimple) {
     std::vector<std::string> values(20, "Temporary data to be overwritten");
     std::vector<ColumnFamilyHandle*> cfs(keys.size(), handles_[1]);
 
+    get_perf_context()->Reset();
     std::vector<Status> s = db_->MultiGet(ReadOptions(), cfs, keys, &values);
     ASSERT_EQ(values.size(), keys.size());
     ASSERT_EQ(values[0], "v1");
     ASSERT_EQ(values[1], "v2");
     ASSERT_EQ(values[2], "v3");
     ASSERT_EQ(values[4], "v5");
+    // four kv pairs * two bytes per value
+    ASSERT_EQ(8, (int)get_perf_context()->multiget_read_bytes);
 
     ASSERT_OK(s[0]);
     ASSERT_OK(s[1]);
@@ -751,6 +755,7 @@ TEST_F(DBBasicTest, MultiGetSimple) {
     ASSERT_TRUE(s[3].IsNotFound());
     ASSERT_OK(s[4]);
     ASSERT_TRUE(s[5].IsNotFound());
+    SetPerfLevel(kDisable);
   } while (ChangeCompactOptions());
 }
 

db/db_impl.cc

@@ -990,6 +990,7 @@ Status DBImpl::GetImpl(const ReadOptions& read_options,
     size_t size = pinnable_val->size();
     RecordTick(stats_, BYTES_READ, size);
     MeasureTime(stats_, BYTES_PER_READ, size);
+    PERF_COUNTER_ADD(get_read_bytes, size);
   }
   return s;
 }
@@ -1117,6 +1118,7 @@ std::vector<Status> DBImpl::MultiGet(
   RecordTick(stats_, NUMBER_MULTIGET_KEYS_READ, num_keys);
   RecordTick(stats_, NUMBER_MULTIGET_BYTES_READ, bytes_read);
   MeasureTime(stats_, BYTES_PER_MULTIGET, bytes_read);
+  PERF_COUNTER_ADD(multiget_read_bytes, bytes_read);
   PERF_TIMER_STOP(get_post_process_time);
 
   return stat_list;

db/db_iter.cc

@@ -86,6 +86,7 @@ class DBIter: public Iterator {
       RecordTick(global_statistics, NUMBER_DB_PREV, prev_count_);
       RecordTick(global_statistics, NUMBER_DB_PREV_FOUND, prev_found_count_);
       RecordTick(global_statistics, ITER_BYTES_READ, bytes_read_);
+      PERF_COUNTER_ADD(iter_read_bytes, bytes_read_);
       ResetCounters();
     }
 
@@ -1014,6 +1015,7 @@ void DBIter::Seek(const Slice& target) {
       if (valid_) {
         RecordTick(statistics_, NUMBER_DB_SEEK_FOUND);
         RecordTick(statistics_, ITER_BYTES_READ, key().size() + value().size());
+        PERF_COUNTER_ADD(iter_read_bytes, key().size() + value().size());
       }
     }
   } else {
@@ -1056,6 +1058,7 @@ void DBIter::SeekForPrev(const Slice& target) {
       if (valid_) {
         RecordTick(statistics_, NUMBER_DB_SEEK_FOUND);
         RecordTick(statistics_, ITER_BYTES_READ, key().size() + value().size());
+        PERF_COUNTER_ADD(iter_read_bytes, key().size() + value().size());
       }
     }
   } else {
@@ -1094,6 +1097,7 @@ void DBIter::SeekToFirst() {
       if (valid_) {
         RecordTick(statistics_, NUMBER_DB_SEEK_FOUND);
         RecordTick(statistics_, ITER_BYTES_READ, key().size() + value().size());
+        PERF_COUNTER_ADD(iter_read_bytes, key().size() + value().size());
       }
     }
   } else {
@@ -1141,6 +1145,7 @@ void DBIter::SeekToLast() {
     if (valid_) {
       RecordTick(statistics_, NUMBER_DB_SEEK_FOUND);
       RecordTick(statistics_, ITER_BYTES_READ, key().size() + value().size());
+      PERF_COUNTER_ADD(iter_read_bytes, key().size() + value().size());
     }
   }
   if (valid_ && prefix_extractor_ && prefix_same_as_start_) {

db/db_iterator_test.cc

@@ -1719,12 +1719,15 @@ TEST_F(DBIteratorTest, IteratorWithLocalStatistics) {
 
   std::vector<port::Thread> threads;
   std::function<void()> reader_func_next = [&]() {
+    SetPerfLevel(kEnableCount);
+    get_perf_context()->Reset();
     Iterator* iter = db_->NewIterator(ReadOptions());
 
     iter->SeekToFirst();
     // Seek will bump ITER_BYTES_READ
-    total_bytes += iter->key().size();
+    uint64_t bytes = 0;
-    total_bytes += iter->value().size();
+    bytes += iter->key().size();
+    bytes += iter->value().size();
     while (true) {
       iter->Next();
       total_next++;
@@ -1733,20 +1736,25 @@ TEST_F(DBIteratorTest, IteratorWithLocalStatistics) {
         break;
       }
       total_next_found++;
-      total_bytes += iter->key().size();
+      bytes += iter->key().size();
-      total_bytes += iter->value().size();
+      bytes += iter->value().size();
     }
 
     delete iter;
+    ASSERT_EQ(bytes, get_perf_context()->iter_read_bytes);
+    SetPerfLevel(kDisable);
+    total_bytes += bytes;
   };
 
   std::function<void()> reader_func_prev = [&]() {
+    SetPerfLevel(kEnableCount);
     Iterator* iter = db_->NewIterator(ReadOptions());
 
     iter->SeekToLast();
     // Seek will bump ITER_BYTES_READ
-    total_bytes += iter->key().size();
+    uint64_t bytes = 0;
-    total_bytes += iter->value().size();
+    bytes += iter->key().size();
+    bytes += iter->value().size();
     while (true) {
       iter->Prev();
       total_prev++;
@@ -1755,11 +1763,14 @@ TEST_F(DBIteratorTest, IteratorWithLocalStatistics) {
         break;
       }
       total_prev_found++;
-      total_bytes += iter->key().size();
+      bytes += iter->key().size();
-      total_bytes += iter->value().size();
+      bytes += iter->value().size();
     }
 
     delete iter;
+    ASSERT_EQ(bytes, get_perf_context()->iter_read_bytes);
+    SetPerfLevel(kDisable);
+    total_bytes += bytes;
   };
 
   for (int i = 0; i < 10; i++) {

include/rocksdb/perf_context.h

@@ -30,6 +30,11 @@ struct PerfContext {
   uint64_t block_read_time;           // total nanos spent on block reads
   uint64_t block_checksum_time;       // total nanos spent on block checksum
   uint64_t block_decompress_time;  // total nanos spent on block decompression
+
+  uint64_t get_read_bytes;       // bytes for vals returned by Get
+  uint64_t multiget_read_bytes;  // bytes for vals returned by MultiGet
+  uint64_t iter_read_bytes;      // bytes for keys/vals decoded by iterator
+
   // total number of internal keys skipped over during iteration.
   // There are several reasons for it:
   // 1. when calling Next(), the iterator is in the position of the previous

monitoring/perf_context.cc

@@ -40,6 +40,9 @@ void PerfContext::Reset() {
   block_read_time = 0;
   block_checksum_time = 0;
   block_decompress_time = 0;
+  get_read_bytes = 0;
+  multiget_read_bytes = 0;
+  iter_read_bytes = 0;
   internal_key_skipped_count = 0;
   internal_delete_skipped_count = 0;
   internal_recent_skipped_count = 0;
@@ -117,6 +120,9 @@ std::string PerfContext::ToString(bool exclude_zero_counters) const {
   PERF_CONTEXT_OUTPUT(block_read_time);
   PERF_CONTEXT_OUTPUT(block_checksum_time);
   PERF_CONTEXT_OUTPUT(block_decompress_time);
+  PERF_CONTEXT_OUTPUT(get_read_bytes);
+  PERF_CONTEXT_OUTPUT(multiget_read_bytes);
+  PERF_CONTEXT_OUTPUT(iter_read_bytes);
   PERF_CONTEXT_OUTPUT(internal_key_skipped_count);
   PERF_CONTEXT_OUTPUT(internal_delete_skipped_count);
   PERF_CONTEXT_OUTPUT(internal_recent_skipped_count);