我们有一个 java 应用程序，我可以说它也使用了相当多的字符串变量。此外，我们将最大内存和初始内存都设置为 256Mb。此后它运行了一段时间，直到最近我们发现它首先是一个 GC，近 2 周后又是一个 GC。因此我们发现FC的平均值是0.2145s，YGC是0.0511s。我们不确定这些值是否合适或导致其他问题？我们决定将内存增加到 512Mb 并查看其他一些 GC 设置，例如 CMS 设置？还应该优化字符串变量的使用等代码吗？通常什么是对象或变量类型将移入旧对象？
Timestamp S0 S1 E O P YGC YGCT FGC FGCT GCT
2752472.6 69.74 0.00 3.67 51.72 44.17 4614 235.630 2 0.429 236.059
2752477.6 69.74 0.00 5.38 51.72 44.17 4614 235.630 2 0.429 236.059
2752482.6 69.74 0.00 7.51 51.72 44.17 4614 235.630 2 0.429 236.059
2752487.6 69.74 0.00 9.52 51.72 44.17 4614 235.630 2 0.429 236.059
2752492.6 69.74 0.00 10.55 51.72 44.17 4614 235.630 2 0.429 236.059
代码片段
BoneCP connectionPool = null;
class ConnectionHandler implements Runnable {
private Socket receivedSocketConn1;
ConnectionHandler(Socket receivedSocketConn1) {
this.receivedSocketConn1=receivedSocketConn1;
}
Connection dbconn = null;
public void run() { // etc
BufferedWriter writeBuffer = null;
BufferedReader readBuffer = null;
String capturedMessage="";
try{
dbconn = connectionPool.getConnection();
dbconn.setAutoCommit(false);
while ((nextChar=readBuffer.read()) != -1){
capturedMessage += (char) nextChar;
if (nextChar == '*')
{
try{
//all queries here.
//for insert query this how i do
Statement stmt1 = null;
stmt1 = dbconn.createStatement();
String insertQuery3 =........
count = stmt9.executeUpdate(insertQuery3);
try{
if ( stmt1!= null ){ stmt1.close();
}
else{
System.out.println("No stm1 exist");
}
}catch(SQLException ex){
System.out.println("SQLException has been caught for stmt1");
ex.printStackTrace(System.out);
}
///For select we do this
Statement stmt2 = null;
stmt2 = dbconn.createStatement();
String selectQuery2= .........
ResultSet rs2 = stmt2.executeQuery(selectQuery2);
if(rs2.next())
{
}
try{
if ( rs2!= null ){
rs2.close();
} else{
System.out.println("No rs2 exist");
}
if ( stmt2!= null ){
stmt2.close();
} else{
System.out.println("No stm2 exist");
}
}catch(SQLException ex)
{
System.out.println("SQLException has been caught for stmt2");
ex.printStackTrace(System.out);
}
dbconn.commit
}
catch (SQLException ex){
ex.printStackTrace(System.out);
try{
dbconn.rollback();
}
catch (Exception rollback){
rollback.printStackTrace(System.out);
}
}
catch (Exception e){
e.printStackTrace(System.out);
try{
dbconn.rollback();
}
catch (Exception rollback){
rollback.printStackTrace(System.out);
}
}
finally
{
}
}
catch (SocketTimeoutException ex){
ex.printStackTrace();
}
catch (IOException ex){
ex.printStackTrace();
}
catch (Exception ex){
ex.printStackTrace(System.out);
}
finally{
try{
if ( dbconn != null ){
dbconn.close();
}
else{
System.out.println("dbConn is null in finally close");
}
}
catch(SQLException ex){
ex.printStackTrace();
}
try{
if ( writeBuffer != null ){
writeBuffer.close();
}
else{
System.out.println("w is null in finally close");
}
}
catch(IOException ex){
ex.printStackTrace(System.out);
}
}
}
}
来自 sun.misc.Launcher$ExtClassLoader @ 0xe003a648 (50%) 的终结器分析 大小：11.2 MB 类：196 对象：201.7k 类加载器：7
共有 91 个对象实现了 finalize 方法。
Histogram of Objects with Finalize Method
Class Name Objects Shallow Heap
com.mysql.jdbc.JDBC4Connection
First 10 of 38 objects 38 42,560
java.net.SocksSocketImpl
First 10 of 39 objects 39 4,368
java.util.jar.JarFile
All 6 objects 6 384
java.util.zip.Inflater
All 6 objects 6 192
java.util.concurrent.ScheduledThreadPoolExecutor
All 1 objects 1 80
java.util.concurrent.ThreadPoolExecutor
All 1 objects 1 72
Total: 6 entries
91 47,656
终结器分析来自
(46%) 大小：13.6 MB 类：578 个对象：304.8k 类加载器：4
共有 19,341 个对象实现了 finalize 方法。
Class Name Objects Shallow Heap
java.net.SocksSocketImpl
First 10 of 18,354 objects 18,354 2,055,648
com.sun.mail.smtp.SMTPTransport
First 10 of 162 objects 162 25,920
java.io.FileOutputStream
First 10 of 742 objects 742 23,744
com.mysql.jdbc.JDBC4Connection
First 10 of 15 objects 15 16,800
java.util.jar.JarFile
First 10 of 20 objects 20 1,280
java.util.zip.Inflater
First 10 of 25 objects 25 800
java.util.concurrent.ThreadPoolExecutor
All 8 objects 8 576
sun.net.www.protocol.jar.URLJarFile
All 5 objects 5 400
java.util.concurrent.ScheduledThreadPoolExecutor
All 2 objects 2 160
java.lang.ClassLoader$NativeLibrary
All 4 objects 4 128
java.io.FileInputStream
All 3 objects 3 96
sun.jdbc.odbc.JdbcOdbcDriver
All 1 objects 1 24
Total: 12 entries
19,341 2,125,576
来自 org.rzo.yajsw.boot.WrapperClassLoader @ 0xe02818c0 (4%) 的终结器分析 大小：966.3 KB 类：361 对象：19.9k 类加载器：3
共有 22 个对象实现了 finalize 方法。
Histogram of Objects with Finalize Method
Class Name Objects Shallow Heap
java.util.jar.JarFile
First 10 of 11 objects 11 704
java.util.zip.Inflater
All 10 objects 10 320
java.util.concurrent.ThreadPoolExecutor
All 1 objects 1 72
Total: 3 entries
22 1,096
Histo 实时结果。
num #instances #bytes class name
----------------------------------------------
1: 6001 18078232 [I
2: 44562 7196072 [B
3: 103183 6054240 [C
4: 31832 4786936 <constMethodKlass>
5: 31832 4340240 <methodKlass>
6: 31638 3543456 java.net.SocksSocketImpl
7: 20127 3542352 com.mysql.jdbc.JDBC4ResultSet
8: 41022 3461576 [Ljava.util.HashMap$Entry;
9: 104185 3333920 java.lang.String
10: 20198 3070096 com.mysql.jdbc.StatementImpl
11: 20323 2926512 com.mysql.jdbc.Field
12: 60329 2895792 java.util.TreeMap
13: 2343 2800032 <constantPoolKlass>
14: 61239 2449560 java.util.TreeMap$Entry
15: 149690 2395040 java.lang.Object
16: 41000 1968000 java.util.HashMap
17: 2343 1895080 <instanceKlassKlass>
18: 1954 1569536 <constantPoolCacheKlass>
19: 31623 1517904 java.net.SocketInputStream
套接字的初始开始
71: 2 224 java.net.SocksSocketImpl
176: 1 32 java.net.Socket
202: 1 24 java.net.InetSocketAddress
206: 1 24 java.net.ServerSocket
运行 50 个套接字后。
19: 52 5824 java.net.SocksSocketImpl
37: 50 2400 java.net.SocketInputStream
48: 51 1632 java.net.Socket
88: 8 384 java.net.SocketOutputStream
95: 8 320 java.net.SocketTimeoutException
135: 7 112 java.net.Socket$3
136: 7 112 java.net.Socket$2
229: 1 24 java.net.ServerSocket