Fix some MultiGet stats (#10673)

Summary:
The stats were not accurate for the coroutine version of MultiGet. This PR fixes it.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10673

Reviewed By: akankshamahajan15

Differential Revision: D39492615

Pulled By: anand1976

fbshipit-source-id: b46c04e15ea27e66f4c31f00c66497aa283bf9d3

HISTORY.md

@@ -9,6 +9,7 @@
 * Update rocksdb.multiget.io.batch.size stat in non-async MultiGet as well.
 * Fix a bug in key range overlap checking with concurrent compactions when user-defined timestamp is enabled. User-defined timestamps should be EXCLUDED when checking if two ranges overlap.
 * Fixed a bug where the blob cache prepopulating logic did not consider the secondary cache (see #10603).
+* Fixed the rocksdb.num.sst.read.per.level, rocksdb.num.index.and.filter.blocks.read.per.level and rocksdb.num.level.read.per.multiget stats in the MultiGet coroutines
 
 ### Public API changes
 * Add `rocksdb_column_family_handle_get_id`, `rocksdb_column_family_handle_get_name` to get name, id of column family in C API

db/version_set.cc

@@ -2655,8 +2655,8 @@ Status Version::ProcessBatch(
     std::unordered_map<uint64_t, BlobReadContexts>* blob_ctxs,
     autovector<FilePickerMultiGet, 4>& batches, std::deque<size_t>& waiting,
     std::deque<size_t>& to_process, unsigned int& num_tasks_queued,
-    uint64_t& num_filter_read, uint64_t& num_index_read,
-    uint64_t& num_sst_read) {
+    std::unordered_map<int, std::tuple<uint64_t, uint64_t, uint64_t>>&
+        mget_stats) {
   FilePickerMultiGet& fp = *batch;
   MultiGetRange range = fp.GetRange();
   // Initialize a new empty range. Any keys that are not in this level will
@@ -2706,19 +2706,29 @@ Status Version::ProcessBatch(
     leftover += ~file_range;
     range -= ~file_range;
     if (!file_range.empty()) {
+      int level = fp.GetHitFileLevel();
+      auto stat = mget_stats.find(level);
+      if (stat == mget_stats.end()) {
+        auto entry = mget_stats.insert({level, {0, 0, 0}});
+        assert(entry.second);
+        stat = entry.first;
+      }
+
       if (waiting.empty() && to_process.empty() &&
           !fp.RemainingOverlapInLevel() && leftover.empty() &&
           mget_tasks.empty()) {
         // All keys are in one SST file, so take the fast path
         s = MultiGetFromSST(read_options, file_range, fp.GetHitFileLevel(),
                             skip_filters, skip_range_deletions, f, *blob_ctxs,
-                            table_handle, num_filter_read, num_index_read,
-                            num_sst_read);
+                            table_handle, std::get<0>(stat->second),
+                            std::get<1>(stat->second),
+                            std::get<2>(stat->second));
       } else {
         mget_tasks.emplace_back(MultiGetFromSSTCoroutine(
             read_options, file_range, fp.GetHitFileLevel(), skip_filters,
-            skip_range_deletions, f, *blob_ctxs, table_handle, num_filter_read,
-            num_index_read, num_sst_read));
+            skip_range_deletions, f, *blob_ctxs, table_handle,
+            std::get<0>(stat->second), std::get<1>(stat->second),
+            std::get<2>(stat->second)));
         ++num_tasks_queued;
       }
     }
@@ -2756,9 +2766,7 @@ Status Version::MultiGetAsync(
   std::deque<size_t> to_process;
   Status s;
   std::vector<folly::coro::Task<Status>> mget_tasks;
-  uint64_t num_filter_read = 0;
-  uint64_t num_index_read = 0;
-  uint64_t num_sst_read = 0;
+  std::unordered_map<int, std::tuple<uint64_t, uint64_t, uint64_t>> mget_stats;
 
   // Create the initial batch with the input range
   batches.emplace_back(range, &storage_info_.level_files_brief_,
@@ -2780,20 +2788,10 @@ Status Version::MultiGetAsync(
       // Look through one level. This may split the batch and enqueue it to
       // to_process
       s = ProcessBatch(options, batch, mget_tasks, blob_ctxs, batches, waiting,
-                       to_process, num_tasks_queued, num_filter_read,
-                       num_index_read, num_sst_read);
+                       to_process, num_tasks_queued, mget_stats);
       if (!s.ok()) {
         break;
       }
-      // Dump the stats since the search has moved to the next level
-      if (num_filter_read + num_index_read) {
-        RecordInHistogram(db_statistics_,
-                          NUM_INDEX_AND_FILTER_BLOCKS_READ_PER_LEVEL,
-                          num_index_read + num_filter_read);
-      }
-      if (num_sst_read) {
-        RecordInHistogram(db_statistics_, NUM_SST_READ_PER_LEVEL, num_sst_read);
-      }
       // If ProcessBatch didn't enqueue any coroutine tasks, it means all
       // keys were filtered out. So put the batch back in to_process to
       // lookup in the next level
@@ -2840,6 +2838,30 @@ Status Version::MultiGetAsync(
     }
   }
 
+  uint64_t num_levels = 0;
+  for (auto& stat : mget_stats) {
+    if (stat.first == 0) {
+      num_levels += std::get<2>(stat.second);
+    } else {
+      num_levels++;
+    }
+
+    uint64_t num_meta_reads =
+        std::get<0>(stat.second) + std::get<1>(stat.second);
+    uint64_t num_sst_reads = std::get<2>(stat.second);
+    if (num_meta_reads > 0) {
+      RecordInHistogram(db_statistics_,
+                        NUM_INDEX_AND_FILTER_BLOCKS_READ_PER_LEVEL,
+                        num_meta_reads);
+    }
+    if (num_sst_reads > 0) {
+      RecordInHistogram(db_statistics_, NUM_SST_READ_PER_LEVEL, num_sst_reads);
+    }
+  }
+  if (num_levels > 0) {
+    RecordInHistogram(db_statistics_, NUM_LEVEL_READ_PER_MULTIGET, num_levels);
+  }
+
   return s;
 }
 #endif

db/version_set.h

@@ -1014,15 +1014,14 @@ class Version {
   // queue coroutine tasks to mget_tasks. It may also split the input batch
   // by creating a new batch with keys definitely not in this level and
   // enqueuing it to to_process.
-  Status ProcessBatch(const ReadOptions& read_options,
-                      FilePickerMultiGet* batch,
-                      std::vector<folly::coro::Task<Status>>& mget_tasks,
-                      std::unordered_map<uint64_t, BlobReadContexts>* blob_ctxs,
-                      autovector<FilePickerMultiGet, 4>& batches,
-                      std::deque<size_t>& waiting,
-                      std::deque<size_t>& to_process,
-                      unsigned int& num_tasks_queued, uint64_t& num_filter_read,
-                      uint64_t& num_index_read, uint64_t& num_sst_read);
+  Status ProcessBatch(
+      const ReadOptions& read_options, FilePickerMultiGet* batch,
+      std::vector<folly::coro::Task<Status>>& mget_tasks,
+      std::unordered_map<uint64_t, BlobReadContexts>* blob_ctxs,
+      autovector<FilePickerMultiGet, 4>& batches, std::deque<size_t>& waiting,
+      std::deque<size_t>& to_process, unsigned int& num_tasks_queued,
+      std::unordered_map<int, std::tuple<uint64_t, uint64_t, uint64_t>>&
+          mget_stats);
 #endif
 
   ColumnFamilyData* cfd_;  // ColumnFamilyData to which this Version belongs