性能调优：主要从以下几个方面入手

• 应用代码：假如代码开发的不好，它会导致性能问题，比如数据库的连接在该关闭的时候没有适当的关闭，将会导致应用运行慢。
• 数据库的调优：如果数据库的响应比较慢，那么应用也肯定就会回应的比较慢了。
• JVM的调优：假如应用需要较多的内存来运行，而你分配比较小的内存，那么就会导致内存溢出，因而也会导致性能问题。
• 中间件服务：比如我们在选择消息队列，缓存或者设计好时，也会导致性能问题。
• 基础架构和OS：比如，网络丢包，系统配置不合理等。

适当的日志记录和监控：日志和监控有助于分析和排错。

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Tomcat连接器的类型：

Java HTTP 连接器：

是基于HTTP协议，支持HTTP1.1，它使tomcat服务器扮演一个独立 服务器和JSP/servlet功能的服务器。

Java AJP 连接器：

JAVA AJP是基于Apache JServ 协议的，该连接器常常是在你不想暴露自己的Java servlet容器到Internet.

APR(AJP/HTTP)连接器：

Apache Portable Runtime（APR）是在扩容，性能和不同web服务器之间的兼容最好 的。它提供了比如OPENSSL，共享内存，Unix大套接字等。

线程调优：

线程沲定义了web服务器连接请求连接的数量，可以定义两种线程沲：一是共享沲，二是专用沲。该配置在TOMCAT_HOME/conf/server.xml文件中定义的。

共享线程沲：

假如你配置了四个连接器，那么你可以共享使用这个线程沲。
配置如下：

（1）定义线程沲

（2）引用定义的线程沲

专用线程沲：也是在server.xml文件中进行定义的

下表是专用线程沲和共享线程沲经常使用场景对比

• Features Shared thread pool Dedicated thread pool
• Number of users less High
• Environment Development Production
• Performance low Good

maxThreads:

默认定义的最大线程沲是150个，在生产环境中，可以根据服务器的性能来调下该参数。

maxKeepAlive:

也相当于并发数一样，默认值是1，也就是相当于关闭。

JVM的调优：

JMAP(内存映射)

JMAP显示共享JAVA虚拟机内存信息，对查看共享内存的状态有用的。下面是一些常用选项：
Options Description

• -dump Dumps the Java heap in hprof binary format
• -finalizer info Prints information on objects awaiting finalization
• -heap Prints a heap summary
• -histo Prints a histogram of the heap
• -permstat Prints class loader-wise statistics of permanent generation of the Java heap

jmap的语法：

./jmap --heap

比如我们的JAVA的ID是4306，那么就执行./jmap -heap 4306

Attaching to process ID 4306, please wait...
Debugger attached successfully.
Client compiler detected.
JVM version is 19.1-b02
using thread-local object allocation.
Mark Sweep Compact GC
Heap Configuration:
MinHeapFreeRatio = 40
MaxHeapFreeRatio = 70
MaxHeapSize = 268435456 (256.0MB)
NewSize = 1048576 (1.0MB)
MaxNewSize = 4294901760 (4095.9375MB)
OldSize = 4194304 (4.0MB)
NewRatio = 2
SurvivorRatio = 8
PermSize = 12582912 (12.0MB)
MaxPermSize = 67108864 (64.0MB)
Heap Usage:
New Generation (Eden + 1 Survivor Space):
capacity = 5111808 (4.875MB)
used = 3883008 (3.703125MB)
free = 1228800 (1.171875MB)
75.96153846153847% used
Eden Space:
capacity = 4587520 (4.375MB)
used = 3708360 (3.5365676879882812MB)
free = 879160 (0.8384323120117188MB)
80.83583286830357% used
From Space:
capacity = 524288 (0.5MB)
used = 174648 (0.16655731201171875MB)
free = 349640 (0.33344268798828125MB)
33.31146240234375% used
To Space:
capacity = 524288 (0.5MB)
used = 0 (0.0MB)
free = 524288 (0.5MB)
0.0% used
tenured generation:
capacity = 11206656 (10.6875MB)
used = 3280712 (3.1287307739257812MB)
free = 7925944 (7.558769226074219MB)
29.274673908077485% used
Perm Generation:
capacity = 12582912 (12.0MB)
used = 6639016 (6.331459045410156MB)
free = 5943896 (5.668540954589844MB)
52.762158711751304% used

从上面看可以看到如下主要信息：

• 应用的堆配置
• 每个JVM组件的堆内存利用率
• 垃圾收集器使用的算法

堆内存的配置：

在catalina.sh中JAVA_OPTS的选项。
JAVA_OPTS="-Xms128m -Xmx512m -XX:MaxPermSize=256m"

垃圾收集器主要有三种方式：

• 串行收集
• 并行收集
• 并发低暂停收集

串行收集的特征如下：

• Features Serial collector
• Process Single thread is used for GC
• GC pause High
• Threading Single threaded
• Application Small application (data less than 100 MB)
• Advantage There is single thread communication

并行收集的特征如下：

• Features Parallel collector
• Process Parallel thread does minor GC
• GC pause Less than Serial
• Threading Multithreaded
• Application Mid-large
• Advantage Used in applications when peak performance is needed

并发收集的特征如下：

• Features Concurrent collector
• Process GC is done concurrently
• GC pause Short pause
• Threading Multithreaded
• Application Mid-large
• Advantage Used in applications when a response is needed

JVM的选项分为标准和非标准：

主要有以下选项：

• Options Parameter Description
• Behavioral Options -XX:+ScavengeBeforeFullGC Do young generation GC prior to a full GC
• Behavioral Options --XX:-UseParallelGC Use parallel garbage collection for scavenges
• Performance Options -XX:MaxNewSize=size Maximum size of new generation (in bytes)
• Performance Options -XX:MaxPermSize=64m Size of the Permanent Generation (after exceeding Xmxvalue)
• Performance Options -Xms Minimum heap memory for the startup of Tomcat
• Performance Options Xmx Maximum memory allocated to the instance
• Performance Options -Xss Stack size for the heap
• Debugging Options -XX:-CITime Prints time spent in the JIT Compiler
• Debugging Options -XX:ErrorFile=./hs_err_pid.log If an error occurs, save the error data to this file
• Debugging Options -XX:HeapDumpPath=./java_pid.hprof Path to the directory or filename for the heap dump
• Debugging Options -XX:-HeapDumpOnOutOfMemoryError Dump the heap to the file whenjava.lang.OutOfMemoryError is thrown
• Options Parameter Description
• Debugging Options -XX:OnError=";" Run user-defined commands on fatal error
• Debugging Options -XX:OnOutOfMemoryError="; Run user-defined commands when an OutOfMemoryError is first thrown
• Debugging Options -XX:-PrintClassHistogram Print a histogram of class instances on Ctrl-Break
• Parameters displayed in the logs for GC
• GC prints the output of the garbage collection to the stdout stream. At every garbage collection, the following five fields are printed:

• [%T %B->%A(%C), %D]

• %T: This is "GC" when the garbage collection is a scavenge, and "Full GC:" is performed, then scavenge collects live objects from the new generation only, whereas a full garbage collection collects objects from all spaces in the Java heap.
• %B: It is the size of the Java heap used before the garbage collection, in KB.
• %A: It is the size of the Java heap after the garbage collection, in KB.
• %C: It is the current capacity of the entire Java heap, in KB.

• %D: It is the duration of the collection in seconds.

• SurvivorRatio
• It is defined as a ratio of eden to the survivor space size. The default value is 8, meaning that eden is 8 times bigger than from and to, each. The syntax for the SurvivorRatio is -XX:SurvivorRatio=.
• The following are some examples:

系统调优：

• 建议选择64位系统
• 文件尺寸限制
• 打开连接限制
• 大页面尺寸

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