Divide `NO_ITERATORS` into two counters `NO_ITERATOR_CREATED` and `NO_ITERATOR_DELETE` (#4498)

Summary:
Currently, `Statistics` can record tick by `recordTick()` whose second parameter is an `uint64_t`.
That means tick can only increase.
If we want to reduce tick, we have to work around like `RecordTick(statistics_, NO_ITERATORS, uint64_t(-1));`.
That's kind of a hack.

So, this PR divide `NO_ITERATORS` into two counters `NO_ITERATOR_CREATED` and `NO_ITERATOR_DELETE`, making the counters increase only.

Fixes #3013 .
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4498

Differential Revision: D10395010

Pulled By: sagar0

fbshipit-source-id: cfb523b22a37411c794b4e9da090f1ae30293db2

HISTORY.md

@@ -1,5 +1,7 @@
 # Rocksdb Change Log
 ## Unreleased
+### Public API Change
+* `NO_ITERATORS` is divided into two counters `NO_ITERATOR_CREATED` and `NO_ITERATOR_DELETE`. Both of them are only increasing now, just as other counters.
 
 ## 5.18.0 (11/12/2018)
 ### New Features

db/db_iter.cc

@@ -142,7 +142,7 @@ class DBIter final: public Iterator {
         allow_blob_(allow_blob),
         is_blob_(false),
         start_seqnum_(read_options.iter_start_seqnum) {
-    RecordTick(statistics_, NO_ITERATORS);
+    RecordTick(statistics_, NO_ITERATOR_CREATED);
     prefix_extractor_ = mutable_cf_options.prefix_extractor.get();
     max_skip_ = max_sequential_skip_in_iterations;
     max_skippable_internal_keys_ = read_options.max_skippable_internal_keys;
@@ -158,9 +158,7 @@ class DBIter final: public Iterator {
     if (pinned_iters_mgr_.PinningEnabled()) {
       pinned_iters_mgr_.ReleasePinnedData();
     }
-    // Compiler warning issue filed:
+    RecordTick(statistics_, NO_ITERATOR_DELETED);
-    // https://github.com/facebook/rocksdb/issues/3013
-    RecordTick(statistics_, NO_ITERATORS, uint64_t(-1));
     ResetInternalKeysSkippedCounter();
     local_stats_.BumpGlobalStatistics(statistics_);
     if (!arena_mode_) {

include/rocksdb/statistics.h

@@ -155,7 +155,7 @@ enum Tickers : uint32_t {
   // Disabled by default. To enable it set stats level to kAll
   DB_MUTEX_WAIT_MICROS,
   RATE_LIMIT_DELAY_MILLIS,
-  NO_ITERATORS,  // number of iterators currently open
+  NO_ITERATOR_CREATED,  // number of iterators created
 
   // Number of MultiGet calls, keys read, and bytes read
   NUMBER_MULTIGET_CALLS,
@@ -322,6 +322,8 @@ enum Tickers : uint32_t {
   // 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,
+
+  NO_ITERATOR_DELETED,  // number of iterators deleted
   TICKER_ENUM_MAX
 };
 
@@ -392,7 +394,7 @@ const std::vector<std::pair<Tickers, std::string>> TickersNameMap = {
     {STALL_MICROS, "rocksdb.stall.micros"},
     {DB_MUTEX_WAIT_MICROS, "rocksdb.db.mutex.wait.micros"},
     {RATE_LIMIT_DELAY_MILLIS, "rocksdb.rate.limit.delay.millis"},
-    {NO_ITERATORS, "rocksdb.num.iterators"},
+    {NO_ITERATOR_CREATED, "rocksdb.num.iterator.created"},
     {NUMBER_MULTIGET_CALLS, "rocksdb.number.multiget.get"},
     {NUMBER_MULTIGET_KEYS_READ, "rocksdb.number.multiget.keys.read"},
     {NUMBER_MULTIGET_BYTES_READ, "rocksdb.number.multiget.bytes.read"},
@@ -474,6 +476,7 @@ const std::vector<std::pair<Tickers, std::string>> TickersNameMap = {
     {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"},
+    {NO_ITERATOR_DELETED, "rocksdb.num.iterator.deleted"},
 };
 
 /**

java/rocksjni/portal.h

@@ -3301,7 +3301,7 @@ class TickerTypeJni {
         return 0x36;
       case rocksdb::Tickers::RATE_LIMIT_DELAY_MILLIS:
         return 0x37;
-      case rocksdb::Tickers::NO_ITERATORS:
+      case rocksdb::Tickers::NO_ITERATOR_CREATED:
         return 0x38;
       case rocksdb::Tickers::NUMBER_MULTIGET_CALLS:
         return 0x39;
@@ -3379,8 +3379,10 @@ class TickerTypeJni {
         return 0x5D;
       case rocksdb::Tickers::NUMBER_MULTIGET_KEYS_FOUND:
         return 0x5E;
-      case rocksdb::Tickers::TICKER_ENUM_MAX:
+      case rocksdb::Tickers::NO_ITERATOR_DELETED:
         return 0x5F;
+      case rocksdb::Tickers::TICKER_ENUM_MAX:
+        return 0x60;
 
       default:
         // undefined/default
@@ -3505,7 +3507,7 @@ class TickerTypeJni {
       case 0x37:
         return rocksdb::Tickers::RATE_LIMIT_DELAY_MILLIS;
       case 0x38:
-        return rocksdb::Tickers::NO_ITERATORS;
+        return rocksdb::Tickers::NO_ITERATOR_CREATED;
       case 0x39:
         return rocksdb::Tickers::NUMBER_MULTIGET_CALLS;
       case 0x3A:
@@ -3583,6 +3585,8 @@ class TickerTypeJni {
       case 0x5E:
         return rocksdb::Tickers::NUMBER_MULTIGET_KEYS_FOUND;
       case 0x5F:
+        return rocksdb::Tickers::NO_ITERATOR_DELETED;
+      case 0x60:
         return rocksdb::Tickers::TICKER_ENUM_MAX;
 
       default:

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

@@ -304,9 +304,9 @@ public enum TickerType {
     RATE_LIMIT_DELAY_MILLIS((byte) 0x37),
 
     /**
-     * Number of iterators currently open.
+     * Number of iterators created.
      */
-    NO_ITERATORS((byte) 0x38),
+    NO_ITERATOR_CREATED((byte) 0x38),
 
     /**
      * Number of MultiGet calls.
@@ -475,7 +475,12 @@ public enum TickerType {
      */
     NUMBER_MULTIGET_KEYS_FOUND((byte) 0x5E),
 
-    TICKER_ENUM_MAX((byte) 0x5F);
+    /**
+     * Number of iterators deleted.
+     */
+    NO_ITERATOR_DELETED((byte) 0x5F),
+
+    TICKER_ENUM_MAX((byte) 0x60);
 
 
     private final byte value;