Archive for 十月, 2005


JVM Heap Space问题

Java Heap Size Options


You achieve best performance by individually tuning each of your applications. Configuring the JVM heap size options listed in Table 2-2 increases performance for most applications.


The options listed in Table 2-2 may differ depending on your architecture and operating system. See your vendor’s documentation for platform-specific JVM tuning options.




Table 2-2 Java Heap Size Options





























Task


Option


Description


Setting the New generation heap size


-XX:NewSize


Use this option to set the New generation Java heap size. Set this value to a multiple of 1024 that is greater than 1MB. As a general rule, set -XX:NewSize to be one-fourth the size of the maximum heap size. Increase the value of this option for larger numbers of short-lived objects.


Be sure to increase the New generation as you increase the number of processors. Memory allocation can be parallel, but garbage collection is not parallel.


Setting the maximum New generation heap size


-XX:MaxNewSize


Use this option to set the maximum New generation Java heap size. Set this value to a multiple of 1024 that is greater than 1MB.


Setting New heap size ratios


-XX:SurvivorRatio


The New generation area is divided into three sub-areas: Eden, and two survivor spaces that are equal in size.


Use the -XX:SurvivorRatio=X option to configure the ratio of the Eden/survivor space size. Try setting this value to 8 and then monitor your garbage collection.


Setting minimum heap size


-Xms


Use this option to set the minimum size of the memory allocation pool. Set this value to a multiple of 1024 that is greater than 1MB. As a general rule, set minimum heap size (-Xms) equal to the maximum heap size (-Xmx).


Setting maximum heap size


-Xmx


Use this option to set the maximum Java heap size. Set this value to a multiple of 1024 that is greater than 1MB.



 

2台mysql server:
192.168.0.11 (master)
192.168.0.12 (slave)


如果要在master-slave之间复制bbs库,首先


在master上创建replication用户(赋予‘复制’权限):
mysql>GRANT REPLICATION SLAVE ON *.*
TO ‘repl’@'%’ IDENTIFIED BY ’slavepass’;


mysql>GRANT FILE ON *.* TO ‘repl’@'%’ IDENTIFIED BY ’slavepass’;


锁定只能操作读权限
mysql>FLUSH TABLES WITH READ LOCK;


在master上创建bbs库的快照(snapshot)
tar -cvf /tmp/bbs.tar ./bbs


在slave上还原快照:
tar -xvf /tmp/bbs.tar


mysql> UNLOCK TABLES;


修改slave上/etc/my.cnf
[mysqld]
master-host=192.168.0.11
master-user=repl
master-password=slavepass
master-port=3306
server-id=2
master-connect-retry=60
replicate-do-db=bbs
log-slave-updates


master服务器修改my.cnf文件,一般路径在/etc/my.cnf,添加如下内容:
[mysqld]
log-bin
server-id=1  #分配一个id
sql-bin-update-same 
binlog-do-db=bbs #要同步的库名


master
mysql > SHOW MASTER STATUS;


slave
mysql > SHOW SLAVE STATUS;

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