mysql-SQLError:1205,SQLState:41000

[WARN ] 2015-04-19 09:00:00,760 method:org.hibernate.util.JDBCExceptionReporter.logExceptions(JDBCExceptionReporter.java:77)
SQL Error: 1205, SQLState: 41000
[ERROR] 2015-04-19 09:00:00,764 method:org.hibernate.util.JDBCExceptionReporter.logExceptions(JDBCExceptionReporter.java:78)
Lock wait timeout exceeded; try restarting transaction
[ERROR] 2015-04-19 09:00:00,765 method:com.opensymphony.xwork2.util.logging.commons.CommonsLogger.error(CommonsLogger.java:38)
Exception occurred during processing request: could not execute update query
org.hibernate.exception.GenericJDBCException: could not execute update query
at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:103)
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:91)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
Caused by: java.sql.SQLException: Lock wait timeout exceeded; try restarting transaction
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1073)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4096)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4028)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2490)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2651)
当时网站不能访问，tomcat的进程还在，重启tomcat就好了，最近每礼拜周末都来一次
求助各位大大这是咋回事儿