日志文件比较大时，使用语句减少大小。

USE DATABASENAME;
GO
-- Truncate the log by changing the database recovery model to SIMPLE.
ALTER DATABASE DATABASENAME
SET RECOVERY SIMPLE;
GO
-- Shrink the truncated log file to 1 MB.
DBCC SHRINKFILE (DATABASENAME_Log, 1);
GO
-- Reset the database recovery model.
ALTER DATABASE DATABASENAME
SET RECOVERY FULL;
GO