Add a stat for MultiGet keys found, update memtable hit/miss stats

Summary:
1. Add a new ticker stat rocksdb.number.multiget.keys.found to track the
number of keys successfully read
2. Update rocksdb.memtable.hit/miss in DBImpl::MultiGet(). It was being done in
DBImpl::GetImpl(), but not MultiGet
Closes https://github.com/facebook/rocksdb/pull/3730

Differential Revision: D7677364

Pulled By: anand1976

fbshipit-source-id: af22bd0ef8ddc5cf2b4244b0a024e539fe48bca5

HISTORY.md

@@ -3,6 +3,7 @@
 ### Public API Change
 * Add a BlockBasedTableOption to align uncompressed data blocks on the smaller of block size or page size boundary, to reduce flash reads by avoiding reads spanning 4K pages.
 * The background thread naming convention changed (on supporting platforms) to "rocksdb:<thread pool priority><thread number>", e.g., "rocksdb:low0".
+* Add a new ticker stat rocksdb.number.multiget.keys.found to count number of keys successfully read in MultiGet calls
 
 ### New Features
 * Introduce TTL for level compaction so that all files older than ttl go through the compaction process to get rid of old data.

db/db_impl.cc

@@ -1164,6 +1164,7 @@ std::vector<Status> DBImpl::MultiGet(
   // First look in the memtable, then in the immutable memtable (if any).
   // s is both in/out. When in, s could either be OK or MergeInProgress.
   // merge_operands will contain the sequence of merges in the latter case.
+  size_t num_found = 0;
   for (size_t i = 0; i < num_keys; ++i) {
     merge_context.Clear();
     Status& s = stat_list[i];
@@ -1185,11 +1186,11 @@ std::vector<Status> DBImpl::MultiGet(
       if (super_version->mem->Get(lkey, value, &s, &merge_context,
                                   &range_del_agg, read_options)) {
         done = true;
-        // TODO(?): RecordTick(stats_, MEMTABLE_HIT)?
+        RecordTick(stats_, MEMTABLE_HIT);
       } else if (super_version->imm->Get(lkey, value, &s, &merge_context,
                                          &range_del_agg, read_options)) {
         done = true;
-        // TODO(?): RecordTick(stats_, MEMTABLE_HIT)?
+        RecordTick(stats_, MEMTABLE_HIT);
       }
     }
     if (!done) {
@@ -1198,11 +1199,12 @@ std::vector<Status> DBImpl::MultiGet(
       super_version->current->Get(read_options, lkey, &pinnable_val, &s,
                                   &merge_context, &range_del_agg);
       value->assign(pinnable_val.data(), pinnable_val.size());
-      // TODO(?): RecordTick(stats_, MEMTABLE_MISS)?
+      RecordTick(stats_, MEMTABLE_MISS);
     }
 
     if (s.ok()) {
       bytes_read += value->size();
+      num_found++;
     }
   }
 
@@ -1230,6 +1232,7 @@ std::vector<Status> DBImpl::MultiGet(
 
   RecordTick(stats_, NUMBER_MULTIGET_CALLS);
   RecordTick(stats_, NUMBER_MULTIGET_KEYS_READ, num_keys);
+  RecordTick(stats_, NUMBER_MULTIGET_KEYS_FOUND, num_found);
   RecordTick(stats_, NUMBER_MULTIGET_BYTES_READ, bytes_read);
   MeasureTime(stats_, BYTES_PER_MULTIGET, bytes_read);
   PERF_COUNTER_ADD(multiget_read_bytes, bytes_read);

include/rocksdb/statistics.h

@@ -320,6 +320,9 @@ enum Tickers : uint32_t {
   // # of times snapshot_mutex_ is acquired in the fast path.
   TXN_SNAPSHOT_MUTEX_OVERHEAD,
 
+  // Number of keys actually found in MultiGet calls (vs number requested by caller)
+  // NUMBER_MULTIGET_KEYS_READ gives the number requested by caller
+  NUMBER_MULTIGET_KEYS_FOUND,
   TICKER_ENUM_MAX
 };
 
@@ -471,6 +474,7 @@ const std::vector<std::pair<Tickers, std::string>> TickersNameMap = {
      "rocksdb.txn.overhead.mutex.old.commit.map"},
     {TXN_DUPLICATE_KEY_OVERHEAD, "rocksdb.txn.overhead.duplicate.key"},
     {TXN_SNAPSHOT_MUTEX_OVERHEAD, "rocksdb.txn.overhead.mutex.snapshot"},
+    {NUMBER_MULTIGET_KEYS_FOUND, "rocksdb.number.multiget.keys.found"},
 };
 
 /**

java/rocksjni/portal.h

@@ -3295,8 +3295,10 @@ class TickerTypeJni {
         return 0x5C;
       case rocksdb::Tickers::NUMBER_ITER_SKIP:
         return 0x5D;
-      case rocksdb::Tickers::TICKER_ENUM_MAX:
+      case rocksdb::Tickers::NUMBER_MULTIGET_KEYS_FOUND:
         return 0x5E;
+      case rocksdb::Tickers::TICKER_ENUM_MAX:
+        return 0x5F;
 
       default:
         // undefined/default
@@ -3497,6 +3499,8 @@ class TickerTypeJni {
       case 0x5D:
         return rocksdb::Tickers::NUMBER_ITER_SKIP;
       case 0x5E:
+        return rocksdb::Tickers::NUMBER_MULTIGET_KEYS_FOUND;
+      case 0x5F:
         return rocksdb::Tickers::TICKER_ENUM_MAX;
 
       default:

java/src/main/java/org/rocksdb/TickerType.java

@@ -465,7 +465,17 @@ public enum TickerType {
      */
     NUMBER_RATE_LIMITER_DRAINS((byte) 0x5C),
 
-    TICKER_ENUM_MAX((byte) 0x5D);
+    /**
+     * Number of internal skipped during iteration
+     */
+    NUMBER_ITER_SKIP((byte) 0x5D),
+
+    /**
+     * Number of MultiGet keys found (vs number requested)
+     */
+    NUMBER_MULTIGET_KEYS_FOUND((byte) 0x5E),
+
+    TICKER_ENUM_MAX((byte) 0x5F);
 
 
     private final byte value;