buffer size already checked in buffer pool
when rarely conditon ,write queue is empty and cur writing not finished
write header to buffer and not direct write bytes
and child log example
Volatile内部变量没有必要，因为一个线程操纵
Merge pull request #60 from opencloudb/master

Important bug fix
Merge pull request #61 from wdw1206/master

批量insert计算路由时，字符串的值多了单引号
1.4-dev-begin
Merge branch 'master' of https://github.com/MyCATApache/Mycat-Server
fixed:java.lang.NullPointerException at org.opencloudb.parser.druid.DruidShardingParseInfo.addShardingExpr(DruidShardingParseInfo.java:54)