MySQL Thread Pool: Problem Definition
A new thread pool plugin is now a part of the MySQL Enterprise Edition.
In this blog we will cover the problem that the thread pool is solving
and some high-level description of how it solves this problem.
In the traditional MySQL server model there is a one-to-one mapping between
thread and connection. Even the MySQL server has lots of code where thread
or some abbreviation of thread is actually representing a connection.
Obviously this mapping has served MySQL very well over the years, but there
are some cases where this model don't work so well.
One such case is where there are much more connections executing queries
simultaneously compared to the number of CPUs available in the server. The
MySQL Server also have scalability bottlenecks where performance suffers
when too many connections execute in parallel.
So effectively there are two reasons that can make performance suffer in
the original MySQL Server model.
The first is that many connections executing in parallel means that the
amount of data that the CPUs work on increases. This will decrease the
CPU cache hit rates. Lowering the CPU cache hit rate can have a significant
negative impact on server performance. Actually in some cases the amount
of memory allocated by the connections executing in parallel could at times
even supersede the memory available in the server. In this case we enter a
state called swapping which is very detrimental to performance.
The second problem is that the number of parallel queries and transactions
can have a negative impact on the throughput through the "critical sections"
of the MySQL Server (critical section is where mutexes are applied to
ensure only one CPU changes a certain data structure at a time, when such
a critical section becomes a scalability problem we call it a hot spot).
Statements that writes are more affected since they use more critical
sections.
Neither of those problems can be solved in the operating system scheduler.
However there are some operating systems that have attempted solving this
problem for generic applications on a higher level in the operating system.
Both of those problems have the impact that performance suffers more and
more as the number of statements executed in parallel increases.
In addition there are hot spots where the mutex is held for a longer time
when many concurrent statements and/or transactions are executed in
parallel. One such example is the transaction list in InnoDB where each
transaction is listed in a linked list. Thus when the number of concurrent
transactions increases the time to scan the list increases and the time
holding the lock increases and thus the hot spot becomes even hotter
as the concurrency increases.
Current solutions to these issues exist in InnoDB through use of the
configuration parameter --innodb-thread-concurrency. When this parameter
is set to a nonzero value, this indicates how many threads are
able to run through InnoDB code concurrently. This solution have its
use cases where it works well. It does however have the drawback that
the solution itself contains a hot spot that limits the MySQL server
scalability. It does also not contain any solution to limiting the
number of concurrent transactions.
In a previous alpha version of the MySQL Server (MySQL 6.0) a thread
pool was developed. This thread pool solved the problem with limiting
the number of concurrent threads executing. It did nothing to solve
the problem with limiting the number of concurrent transactions.
It was also a scalability bottleneck in itself. Finally it didn't
solve all issues regarding long queries and blocked queries.
This made it possible for the MySQL Server to become completely
blocked.
When developing the thread pool extension now available in the MySQL
Enterprise Edition we decided to start from a clean plate with the
following requirements:
1) Limit the number of concurrently executing statements to ensure
that each statement execution has sufficient CPU and memory resources
to fulfill its task.
2) Split threads and connection into thread groups that are
independently managed. This is to ensure that the thread pool
plugin itself doesn't become a scalability bottleneck. The
aim is that each thread group has one or zero active threads
at any point in time.
3) Limit the number of concurrently executing transactions
through prioritizing queued connections dependent on if
they have started a transaction or not.
4) Avoid deadlocks when a statement execution becomes long or
when the statement is blocked for some reason for an extended
time.
If you are interested in knowing more details of how the new
thread pool solves these requirements there will be a
webinar on Thursday 20 Oct 2011 at 9.00 PDT. Check here
for details on how to access it.
If you want to try out the thread pool go here.
参考:
http://mikaelronstrom.blogspot.ae/2011/10/mysql-thread-pool-problem-definition.html
MySQL Thread Pool: Problem Definition的更多相关文章
- MySQL thread pool【转】
本文来自:http://blog.chinaunix.net/uid-26896862-id-3993773.html 刚刚经历了淘宝的双11,真实感受到了紧张的氛围.尽管DB淡定的度过,但是历程中的 ...
- mysql thread pool
转自:http://blog.csdn.net/wyzxg/article/details/8258033 mysql 线程处理流程图: Mysql支持单线程和多线程两种连接线程模式,如果单线程,则在 ...
- MySQL学习分享--Thread pool实现
基于<MySQL学习分享--Thread pool>对Thread pool架构设计的详细了解,本文主要对Thread pool的实现进行分析,并根据Mariadb和Percona提供的开 ...
- MySQL线程池(THREAD POOL)的原理
MySQL常用(目前线上使用)的线程调度方式是one-thread-per-connection(每连接一个线程),server为每一个连接创建一个线程来服务,连接断开后,这个线程进入thread_c ...
- Improve Scalability With New Thread Pool APIs
Pooled Threads Improve Scalability With New Thread Pool APIs Robert Saccone Portions of this article ...
- 【MySQL】mysql buffer pool结构分析
转自:http://blog.csdn.net/wyzxg/article/details/7700394 MySQL官网配置说明地址:http://dev.mysql.com/doc/refman/ ...
- 线程安全 Thread Safety Problem scala concurrency 并发
小结: 1.基于java并发模型 Scala concurrency is built on top of the Java concurrency model. 2. 将每个请求放入一个新的线程 T ...
- MySQL--线程池(Thread Pool)
================================================================= 线程池技术 在MySQL社区版中,MySQL使用one-thread ...
- Thread pool引起的程序连接数据库响应慢
数据库版本:percona-mysql 5.6.16 在很长一段时间,都会出现程序连接数据库,出现响应慢的情况,正常在几到几十毫秒之间,但是偶尔会出现上百毫秒的情况: 开始由于开发重新设置并调整过程 ...
随机推荐
- Moto G如何进入开发者选项
最近买了个Moto G做应用开发,突然发现开发者选项居然没有,搜索了一下发现是Google隐藏了此选项. http://allaboutmotog.com/moto-g-how-to-guide/ac ...
- STL 源码分析《5》---- lower_bound and upper_bound 详解
在 STL 库中,关于二分搜索实现了4个函数. bool binary_search (ForwardIterator beg, ForwardIterator end, const T& v ...
- ubuntu命令chmod755
使用方式 : 在终端切换到文件目录 输入 chmod775 hello.py 这样就将hello.py变成了可执行文件 当然作为 python文件 还需要再开头加上 #!/usr/bin/env py ...
- PHP中使用的变量
变量是用于临时的存储值的容器.这些值可以是数字.文本,或者复杂得多的排列组合. 变量在任何编程语言中都居于核心地位,理解它们是使用PHP的关键所在.变量又是指在程序的运行过程中随时可以发生变化的量,是 ...
- Palindrome Number ---- LeetCode 009
Determine whether an integer is a palindrome. Do this without extra space. Some hints: Could negativ ...
- 禁止VMware用户在系统里删除网卡的操作的方法
点击选项-常规-配置参数,如下图所示: 8)点击“添加行”,在新的栏目中,左栏输入:devices.hotplug,右边栏输入:false
- HDU 1053 & HDU 2527 哈夫曼编码
http://acm.hdu.edu.cn/showproblem.php?pid=1053 #include <iostream> #include <cstdio> #in ...
- 转:DataTable.Compute()用法
转自:http://www.cnblogs.com/fanyf/archive/2012/05/11/2495919.html一.DataTable.Compute()方法說明如下 作用: 计算用来传 ...
- c++11编码规范 NULL还是nullptr
0和nullptr/NULL 至于指针(地址值),根据实际选择用0.NULL还是nullptr.对使用了C++11特性的项目,选用nullptr:对于C++03项目,推荐NULL,因为它像是一个指针
- win7录屏工具
psr.exe http://jingyan.baidu.com/article/aa6a2c14d330710d4d19c47c.html