From e03377c7fd86f117c6c64d35955140dab400eb3c Mon Sep 17 00:00:00 2001
From: Manuel Ung <mung@fb.com>
Date: Mon, 6 Nov 2017 10:52:17 -0800
Subject: [PATCH] Add lock wait time as a perf context counter

Summary:
Adds two new counters:

`key_lock_wait_count` counts how many times a lock was blocked by another transaction and had to wait, instead of being granted the lock immediately.
`key_lock_wait_time` counts the time spent acquiring locks.
Closes https://github.com/facebook/rocksdb/pull/3107

Differential Revision: D6217332

Pulled By: lth

fbshipit-source-id: 55d4f46da5550c333e523263422fd61d6a46deb9
---
 include/rocksdb/perf_context.h                 | 5 +++++
 monitoring/perf_context.cc                     | 4 ++++
 utilities/transactions/transaction_lock_mgr.cc | 3 +++
 utilities/transactions/transaction_test.cc     | 6 ++++++
 4 files changed, 18 insertions(+)

diff --git a/include/rocksdb/perf_context.h b/include/rocksdb/perf_context.h
index 1095d063b..3bb7f5c0b 100644
--- a/include/rocksdb/perf_context.h
+++ b/include/rocksdb/perf_context.h
@@ -131,6 +131,11 @@ struct PerfContext {
   // total number of SST table bloom misses
   uint64_t bloom_sst_miss_count;
 
+  // Time spent waiting on key locks in transaction lock manager.
+  uint64_t key_lock_wait_time;
+  // number of times acquiring a lock was blocked by another transaction.
+  uint64_t key_lock_wait_count;
+
   // Total time spent in Env filesystem operations. These are only populated
   // when TimedEnv is used.
   uint64_t env_new_sequential_file_nanos;
diff --git a/monitoring/perf_context.cc b/monitoring/perf_context.cc
index 791f4bdbe..a80b9e470 100644
--- a/monitoring/perf_context.cc
+++ b/monitoring/perf_context.cc
@@ -79,6 +79,8 @@ void PerfContext::Reset() {
   bloom_memtable_miss_count = 0;
   bloom_sst_hit_count = 0;
   bloom_sst_miss_count = 0;
+  key_lock_wait_time = 0;
+  key_lock_wait_count = 0;
 
   env_new_sequential_file_nanos = 0;
   env_new_random_access_file_nanos = 0;
@@ -158,6 +160,8 @@ std::string PerfContext::ToString(bool exclude_zero_counters) const {
   PERF_CONTEXT_OUTPUT(bloom_memtable_miss_count);
   PERF_CONTEXT_OUTPUT(bloom_sst_hit_count);
   PERF_CONTEXT_OUTPUT(bloom_sst_miss_count);
+  PERF_CONTEXT_OUTPUT(key_lock_wait_time);
+  PERF_CONTEXT_OUTPUT(key_lock_wait_count);
   PERF_CONTEXT_OUTPUT(env_new_sequential_file_nanos);
   PERF_CONTEXT_OUTPUT(env_new_random_access_file_nanos);
   PERF_CONTEXT_OUTPUT(env_new_writable_file_nanos);
diff --git a/utilities/transactions/transaction_lock_mgr.cc b/utilities/transactions/transaction_lock_mgr.cc
index a72c2a12f..9485067d5 100644
--- a/utilities/transactions/transaction_lock_mgr.cc
+++ b/utilities/transactions/transaction_lock_mgr.cc
@@ -20,6 +20,7 @@
 #include <string>
 #include <vector>
 
+#include "monitoring/perf_context_imp.h"
 #include "rocksdb/slice.h"
 #include "rocksdb/utilities/transaction_db_mutex.h"
 #include "util/cast_util.h"
@@ -347,6 +348,8 @@ Status TransactionLockMgr::AcquireWithTimeout(
                          &expire_time_hint, &wait_ids);
 
   if (!result.ok() && timeout != 0) {
+    PERF_TIMER_GUARD(key_lock_wait_time);
+    PERF_COUNTER_ADD(key_lock_wait_count, 1);
     // If we weren't able to acquire the lock, we will keep retrying as long
     // as the timeout allows.
     bool timed_out = false;
diff --git a/utilities/transactions/transaction_test.cc b/utilities/transactions/transaction_test.cc
index 80aabb943..0c9ce53ff 100644
--- a/utilities/transactions/transaction_test.cc
+++ b/utilities/transactions/transaction_test.cc
@@ -19,6 +19,7 @@
 #include "db/db_impl.h"
 #include "rocksdb/db.h"
 #include "rocksdb/options.h"
+#include "rocksdb/perf_context.h"
 #include "rocksdb/utilities/transaction.h"
 #include "rocksdb/utilities/transaction_db.h"
 #include "table/mock_table.h"
@@ -187,15 +188,18 @@ TEST_P(TransactionTest, WaitingTxn) {
         ASSERT_EQ(cf_id, 0);
       });
 
+  get_perf_context()->Reset();
   // lock key in default cf
   s = txn1->GetForUpdate(read_options, "foo", &value);
   ASSERT_OK(s);
   ASSERT_EQ(value, "bar");
+  ASSERT_EQ(get_perf_context()->key_lock_wait_count, 0);
 
   // lock key in cfa
   s = txn1->GetForUpdate(read_options, cfa, "foo", &value);
   ASSERT_OK(s);
   ASSERT_EQ(value, "bar");
+  ASSERT_EQ(get_perf_context()->key_lock_wait_count, 0);
 
   auto lock_data = db->GetLockStatusData();
   // Locked keys exist in both column family.
@@ -231,6 +235,8 @@ TEST_P(TransactionTest, WaitingTxn) {
   s = txn2->GetForUpdate(read_options, "foo", &value);
   ASSERT_TRUE(s.IsTimedOut());
   ASSERT_EQ(s.ToString(), "Operation timed out: Timeout waiting to lock key");
+  ASSERT_EQ(get_perf_context()->key_lock_wait_count, 1);
+  ASSERT_GE(get_perf_context()->key_lock_wait_time, 0);
 
   rocksdb::SyncPoint::GetInstance()->DisableProcessing();
   rocksdb::SyncPoint::GetInstance()->ClearAllCallBacks();