Java GC和YGC的发生和下一步行动
我们有一个java应用程序，我可以说它也使用了很多字符串变量。此外，我们在启动时将最大内存和初始内存设置为256Mb。此后，它运行了一段时间，直到最近，我们发现，首先是一个GC，近2周后，又是一个GC。因此，我们发现FC的平均值为0.2145s，YGC为0.0511s。我们不确定这些值是否合适或是否会导致其他结果？我们决定将内存增加到512Mb，并研究其他一些GC设置，如CMS设置？还应该优化代码，例如字符串变量的使用？通常，什么类型的对象或变量会移动到旧对象中Java GC和YGC的发生和下一步行动,java,memory-management,garbage-collection,Java,Memory Management,Garbage Collection,我们有一个java应用程序，我可以说它也使用了很多字符串变量。此外，我们在启动时将最大内存和初始内存设置为256Mb。此后，它运行了一段时间，直到最近，我们发现，首先是一个GC，近2周后，又是一个GC。因此，我们发现FC的平均值为0.2145s，YGC为0.0511s。我们不确定这些值是否合适或是否会导致其他结果？我们决定将内存增加到512Mb，并研究其他一些GC设置，如CMS设置？还应该优化代码，例如字符串变量的使用？通常，什么类型的对象或变量会移动到旧对象中 Timestamp S0
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
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);
}
}
}
}
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
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$NativeLibrary
All 4 objects 4 128
java.io.FileInputStream
All 3 objects 3 96
sun.jdbc.odbc.JdbcOdbcDriver
All 1 objects 1 24
Total: 12 entries
19,341 2,125,576
Histogram of Objects with Finalize Method
Class Name Objects Shallow Heap
java.util.jar.JarFile
First 10 of 11 objects 11 704
java.util.zip.Inflater
All 10 objects 10 320
java.util.concurrent.ThreadPoolExecutor
All 1 objects 1 72
Total: 3 entries
22 1,096
Histogram of Objects with Finalize Method
Class Name Objects Shallow Heap
com.mysql.jdbc.JDBC4Connection
First 10 of 38 objects 38 42,560
java.net.SocksSocketImpl
First 10 of 39 objects 39 4,368
java.util.jar.JarFile
All 6 objects 6 384
java.util.zip.Inflater
All 6 objects 6 192
java.util.concurrent.ScheduledThreadPoolExecutor
All 1 objects 1 80
java.util.concurrent.ThreadPoolExecutor
All 1 objects 1 72
Total: 6 entries
91 47,656
Class Name Objects Shallow Heap
java.net.SocksSocketImpl
First 10 of 18,354 objects 18,354 2,055,648
com.sun.mail.smtp.SMTPTransport
First 10 of 162 objects 162 25,920
java.io.FileOutputStream
First 10 of 742 objects 742 23,744
com.mysql.jdbc.JDBC4Connection
First 10 of 15 objects 15 16,800
java.util.jar.JarFile
First 10 of 20 objects 20 1,280
java.util.zip.Inflater
First 10 of 25 objects 25 800
java.util.concurrent.ThreadPoolExecutor
All 8 objects 8 576
sun.net.www.protocol.jar.URLJarFile
All 5 objects 5 400
java.util.concurrent.ScheduledThreadPoolExecutor
All 2 objects 2 160
java.lang.ClassLoader$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
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
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
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$NativeLibrary
All 4 objects 4 128
java.io.FileInputStream
All 3 objects 3 96
sun.jdbc.odbc.JdbcOdbcDriver
All 1 objects 1 24
Total: 12 entries
19,341 2,125,576
Histogram of Objects with Finalize Method
Class Name Objects Shallow Heap
java.util.jar.JarFile
First 10 of 11 objects 11 704
java.util.zip.Inflater
All 10 objects 10 320
java.util.concurrent.ThreadPoolExecutor
All 1 objects 1 72
Total: 3 entries
22 1,096
num #instances #bytes class name
----------------------------------------------
1: 6001 18078232 [I
2: 44562 7196072 [B
3: 103183 6054240 [C
4: 31832 4786936 <constMethodKlass>
5: 31832 4340240 <methodKlass>
6: 31638 3543456 java.net.SocksSocketImpl
7: 20127 3542352 com.mysql.jdbc.JDBC4ResultSet
8: 41022 3461576 [Ljava.util.HashMap$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
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
512MB听起来没那么多，可能不值得你花时间进一步优化它。顺便说一句，512MB是512兆位 中长期存活的对象最终会出现在老一代 您可以使用内存分析器优化代码，以减少字符串的使用。您可以使用StringBuilder回收对象并降低GC压力，这是导致对象错误地进入永久空间的常见原因
如果将其发挥到极致，您可能会发现您可以消除所有字符串生成，但我怀疑这是否值得，将内存增加到1GB可能更简单/更便宜。中期对象的寿命足够长，可以到达永久空间，然后死亡。长期目标在旧世代持续很长时间。StringBuilder是一个选项，但我看不出有什么需要，因为您只需要多一点内存。我使用你的工具包，但我会先试用VisualVM，因为它是免费的，内置的。你可以用不到500英镑的价格买到64 GB，也就是说每GB大约12美元。节省几美元的内存（当然，假设这是您或您的客户的成本）值得付出多少努力。CMS可以通过同时清理来避免填充旧的gen。如果CMS不能跟上您产生垃圾的速度，即在您填充旧一代之前，它没有清理足够的垃圾，则会发生完全GC。CMS使用更多的CPU，但如果不是这样，您可能会有空闲的CPU。如果您有一台所有CPU大部分时间都很忙的机器，那么使用并行收集器更好。Perm gen不容易清理，但这只在卸载类装入器时发生。您经常这样做吗？perm gen在加载和编译新方法时会增加。小幅度的增长也是正常的。CMS可以再增加10%的CPU，但在你的事业中，我怀疑它会更低。如果您不必担心类装入器，那么就不必担心perm gen。