Schema Changes History数据从哪里来？

SQL Server提供了Schema Changes History report可以用来追踪DDL相关信息。 但是Schema Changes History report的数据是从哪里来的呢？

 

首先我启动SQL Profiler trace然后打开Schema Changes History report（Management studio->Report->Standard report->Schema Changes History report）

 

从Profiler trace我看到下面的SQL 语句：

 

        select@curr_tracefilename
= pathfrom
sys.traces
where is_default = 1
;

        set@curr_tracefilename
= reverse(@curr_tracefilename)

        select@indx 
= PATINDEX(''%\%'', @curr_tracefilename)

        set@curr_tracefilename
= reverse(@curr_tracefilename)

        set@base_tracefilename
= LEFT(@curr_tracefilename,len(@curr_tracefilename)- @indx)
+ ''\log.trc'';

 

        insert into @temp_trace

        selectObjectName

        ,       DatabaseName

        ,      StartTime

        ,       EventClass

        ,       EventSubClass

        ,       ObjectType

        ,       ServerName

        ,       LoginName

        ,       ApplicationName

        ,       ''temp''

        from ::fn_trace_gettable( @base_tracefilename,default
)

        whereEventClass
in(46,47,164)
and EventSubclass = 0and DatabaseID
<>2

 

        update@temp_trace
set ddl_operation =
''CREATE''
where event_class =46

        update@temp_trace
set ddl_operation =
''DROP''
where event_class =47

        update@temp_trace
set ddl_operation =
''ALTER''
where event_class =164

 

        select@d1 =
min(start_time)
from @temp_trace

        set@diff=
datediff(hh,@d1,getdate())

        set@diff=@diff/24;

 

        select  @diff
as difference

        ,       @d1 as
date

        ,       object_type
asobj_type_desc

        ,       *

        from@temp_trace
where object_type not
in(21587)

        order by start_time
desc

end

 

 我们看一下event_class 46,47,164代表什么：

 

 select trace_event_id,name from sys.trace_events where trace_event_id in ('46','47','164')

trace_event_id name

-------------- --------------------------------------------------------------------------------------------------------------------------------

46             Object:Created

47             Object:Deleted

164            Object:Altered

(3 row(s) affected)

 

从上面的内容我们可以看到这个Report只是从Default trace中抓取了创建删除和更改三个事件，然后展现给我们。 所以如果我们Disable了Default trace file，就无法从这张Report中查询到数据。

 

另外如果DDL发生在当前Default trace file开始之前也是显示不出来的，但是我们可以将上面的脚本修改一下，直接用当时的Trace File就可以获得相关信息了（SQL Server 默认会保存5份Trace文件）