From 8a81342c104a78c9d84b2877c111a4cb87e3cdff Mon Sep 17 00:00:00 2001
From: Lloyd-Pottiger <60744015+Lloyd-Pottiger@users.noreply.github.com>
Date: Fri, 10 Jun 2022 21:42:30 +0800
Subject: [PATCH] add some notes about `getMemoryAmount()` and
 `getNumberOfPhysicalCPUCores()` (#5126)

close pingcap/tiflash#5125
---
 dbms/src/Common/getNumberOfPhysicalCPUCores.h   | 1 +
 dbms/src/Storages/DeltaMerge/workload/Handle.h  | 6 ++++--
 libs/libcommon/include/common/getMemoryAmount.h | 1 +
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/dbms/src/Common/getNumberOfPhysicalCPUCores.h b/dbms/src/Common/getNumberOfPhysicalCPUCores.h
index 6f7eaef4bb4..b3ab65a66e5 100644
--- a/dbms/src/Common/getNumberOfPhysicalCPUCores.h
+++ b/dbms/src/Common/getNumberOfPhysicalCPUCores.h
@@ -15,4 +15,5 @@
 #pragma once
 
 /// Get number of CPU cores without hyper-threading.
+/// Note: do not support environment under resource isolation mechanism like Docker, CGroup.
 unsigned getNumberOfPhysicalCPUCores();
diff --git a/dbms/src/Storages/DeltaMerge/workload/Handle.h b/dbms/src/Storages/DeltaMerge/workload/Handle.h
index c4949c15a1f..2bbd1bd409d 100644
--- a/dbms/src/Storages/DeltaMerge/workload/Handle.h
+++ b/dbms/src/Storages/DeltaMerge/workload/Handle.h
@@ -51,14 +51,16 @@ class HandleLock
 
     std::vector<std::unique_lock<std::recursive_mutex>> getLocks(const std::vector<uint64_t> & handles)
     {
-        std::vector<uint64_t> indexes(handles.size());
+        std::vector<uint64_t> indexes;
+        indexes.reserve(handles.size());
         for (const auto & h : handles)
         {
             indexes.push_back(index(h));
         }
         // Sort mutex indexes to avoid dead lock.
         sort(indexes.begin(), indexes.end());
-        std::vector<std::unique_lock<std::recursive_mutex>> locks(indexes.size());
+        std::vector<std::unique_lock<std::recursive_mutex>> locks;
+        locks.reserve(indexes.size());
         for (auto i : indexes)
         {
             locks.push_back(getLockByIndex(i));
diff --git a/libs/libcommon/include/common/getMemoryAmount.h b/libs/libcommon/include/common/getMemoryAmount.h
index 98aa87661c3..0807c6f8e12 100644
--- a/libs/libcommon/include/common/getMemoryAmount.h
+++ b/libs/libcommon/include/common/getMemoryAmount.h
@@ -19,5 +19,6 @@
 /**
 * Returns the size of physical memory (RAM) in bytes.
 * Returns 0 on unsupported platform
+* Note: do not support environment under resource isolation mechanism like Docker, CGroup.
 */
 uint64_t getMemoryAmount();