Add benchmark for GetMergeOperands() (#9785)

Summary:
There's an existing benchmark, "getmergeoperands", but it is unconventional in that it has multiple phases and hardcoded setup parameters.

This PR adds a different one, "readrandomoperands", that follows the pattern of other benchmarks of having a single phase and taking its configuration from existing flags.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9785

Test Plan:
```
$ ./db_bench -benchmarks=mergerandom -merge_operator=StringAppendOperator -write_buffer_size=1048576 -max_bytes_for_level_base=4194304 -target_file_size_base=1048576 -compression_type=none -disable_auto_compactions=true
$ ./db_bench -use_existing_db=true -benchmarks=readrandomoperands -merge_operator=StringAppendOperator -disable_auto_compactions=true -duration=10
...
readrandomoperands :     542.082 micros/op 1844 ops/sec;    0.2 MB/s (11980 of 18999 found)
```

Reviewed By: jay-zhuang

Differential Revision: D35290412

Pulled By: ajkr

fbshipit-source-id: fb367ca614b128cef844a75f0e5d9dd7c3328d85

tools/db_bench_tool.cc

@@ -160,6 +160,7 @@ IF_ROCKSDB_LITE("",
     "randomreplacekeys,"
     "timeseries,"
     "getmergeoperands",
+    "readrandomoperands,"
 
     "Comma-separated list of operations to run in the specified"
     " order. Available benchmarks:\n"
@@ -246,7 +247,11 @@ IF_ROCKSDB_LITE("",
     "key "
     "by doing a Get followed by binary searching in the large sorted list vs "
     "doing a GetMergeOperands and binary searching in the operands which are"
-    "sorted sub-lists. The MergeOperator used is sortlist.h\n");
+    "sorted sub-lists. The MergeOperator used is sortlist.h\n"
+    "\treadrandomoperands -- read random keys using `GetMergeOperands()`. An "
+    "operation includes a rare but possible retry in case it got "
+    "`Status::Incomplete()`. This happens upon encountering more keys than "
+    "have ever been seen by the thread (or eight initially)\n");
 
 DEFINE_int64(num, 1000000, "Number of key/values to place in database");
 
@@ -1541,6 +1546,9 @@ DEFINE_bool(persist_stats_to_disk,
 DEFINE_uint64(stats_history_buffer_size,
               ROCKSDB_NAMESPACE::Options().stats_history_buffer_size,
               "Max number of stats snapshots to keep in memory");
+DEFINE_bool(avoid_flush_during_recovery,
+            ROCKSDB_NAMESPACE::Options().avoid_flush_during_recovery,
+            "If true, avoids flushing the recovered WAL data where possible.");
 DEFINE_int64(multiread_stride, 0,
              "Stride length for the keys in a MultiGet batch");
 DEFINE_bool(multiread_batched, false, "Use the new MultiGet API");
@@ -2502,6 +2510,7 @@ class Benchmark {
   int64_t merge_keys_;
   bool report_file_operations_;
   bool use_blob_db_;  // Stacked BlobDB
+  bool read_operands_;  // read via GetMergeOperands()
   std::vector<std::string> keys_;
 
   class ErrorHandlerListener : public EventListener {
@@ -2892,11 +2901,11 @@ class Benchmark {
         merge_keys_(FLAGS_merge_keys < 0 ? FLAGS_num : FLAGS_merge_keys),
         report_file_operations_(FLAGS_report_file_operations),
 #ifndef ROCKSDB_LITE
-        use_blob_db_(FLAGS_use_blob_db)  // Stacked BlobDB
+        use_blob_db_(FLAGS_use_blob_db),  // Stacked BlobDB
 #else
-        use_blob_db_(false)  // Stacked BlobDB
+        use_blob_db_(false),  // Stacked BlobDB
 #endif  // !ROCKSDB_LITE
-  {
+        read_operands_(false) {
     // use simcache instead of cache
     if (FLAGS_simcache_size >= 0) {
       if (FLAGS_cache_numshardbits >= 1) {
@@ -3409,6 +3418,9 @@ class Benchmark {
       } else if (name == "verifyfilechecksums") {
         method = &Benchmark::VerifyFileChecksums;
 #endif                             // ROCKSDB_LITE
+      } else if (name == "readrandomoperands") {
+        read_operands_ = true;
+        method = &Benchmark::ReadRandom;
       } else if (!name.empty()) {  // No error message for empty name
         fprintf(stderr, "unknown benchmark '%s'\n", name.c_str());
         ErrorExit();
@@ -4294,6 +4306,7 @@ class Benchmark {
     options.persist_stats_to_disk = FLAGS_persist_stats_to_disk;
     options.stats_history_buffer_size =
         static_cast<size_t>(FLAGS_stats_history_buffer_size);
+    options.avoid_flush_during_recovery = FLAGS_avoid_flush_during_recovery;
 
     options.compression_opts.level = FLAGS_compression_level;
     options.compression_opts.max_dict_bytes = FLAGS_compression_max_dict_bytes;
@@ -5634,6 +5647,12 @@ class Benchmark {
     std::unique_ptr<const char[]> key_guard;
     Slice key = AllocateKey(&key_guard);
     PinnableSlice pinnable_val;
+    std::vector<PinnableSlice> pinnable_vals;
+    if (read_operands_) {
+      // Start off with a small-ish value that'll be increased later if
+      // `GetMergeOperands()` tells us it is not large enough.
+      pinnable_vals.resize(8);
+    }
     std::unique_ptr<char[]> ts_guard;
     Slice ts;
     if (user_timestamp_size_ > 0) {
@@ -5671,17 +5690,45 @@ class Benchmark {
       }
       Status s;
       pinnable_val.Reset();
+      for (size_t i = 0; i < pinnable_vals.size(); ++i) {
+        pinnable_vals[i].Reset();
+      }
+      ColumnFamilyHandle* cfh;
       if (FLAGS_num_column_families > 1) {
-        s = db_with_cfh->db->Get(options, db_with_cfh->GetCfh(key_rand), key,
-                                 &pinnable_val, ts_ptr);
+        cfh = db_with_cfh->GetCfh(key_rand);
       } else {
-        s = db_with_cfh->db->Get(options,
-                                 db_with_cfh->db->DefaultColumnFamily(), key,
-                                 &pinnable_val, ts_ptr);
+        cfh = db_with_cfh->db->DefaultColumnFamily();
+      }
+      if (read_operands_) {
+        GetMergeOperandsOptions get_merge_operands_options;
+        get_merge_operands_options.expected_max_number_of_operands =
+            static_cast<int>(pinnable_vals.size());
+        int number_of_operands;
+        s = db_with_cfh->db->GetMergeOperands(
+            options, cfh, key, pinnable_vals.data(),
+            &get_merge_operands_options, &number_of_operands);
+        if (s.IsIncomplete()) {
+          // Should only happen a few times when we encounter a key that had
+          // more merge operands than any key seen so far. Production use case
+          // would typically retry in such event to get all the operands so do
+          // that here.
+          pinnable_vals.resize(number_of_operands);
+          get_merge_operands_options.expected_max_number_of_operands =
+              static_cast<int>(pinnable_vals.size());
+          s = db_with_cfh->db->GetMergeOperands(
+              options, cfh, key, pinnable_vals.data(),
+              &get_merge_operands_options, &number_of_operands);
+        }
+      } else {
+        s = db_with_cfh->db->Get(options, cfh, key, &pinnable_val, ts_ptr);
       }
+
       if (s.ok()) {
         found++;
         bytes += key.size() + pinnable_val.size() + user_timestamp_size_;
+        for (size_t i = 0; i < pinnable_vals.size(); ++i) {
+          bytes += pinnable_vals[i].size();
+        }
       } else if (!s.IsNotFound()) {
         fprintf(stderr, "Get returned an error: %s\n", s.ToString().c_str());
         abort();