INF: Determining User Segments from Segmap Values

ID: Q101241

The information in this article applies to:

SUMMARY

This article describes a stored procedure which can be used to determine which user segments map to a Microsoft SQL Server device based on the values from the master.dbo.sysusages segmap column.


MORE INFORMATION

One difficulty in administering databases in which user segments have been defined is determining which segments map to each database device.

Each user segment in a database is assigned a segment number unique in that database, this number is recorded in the dbo.syssegments table in each database. The master.dbo.sysusages table indicates how each database maps to its devices. The segmap column in the sysusages table holds the information about which segments map onto each device.

The stored procedure has been kept simple so that users can run it even in new systems to which they have not yet migrated user databases. The syntax is:

execute sp_segmap <segmap value>

sp_segmap returns a column segment_num which contains segment numbers which will match the column segment in the table dbo.syssegments in the user database.

Example

For an example of sp_segmap's use, assume that a database has one line in sysusages which has a segmap value of 7.
execute sp_segmap 7

returns segment_num values of 0, 1, and 2. Looking in the syssegments table for that database will show that segments 0, 1, and 2 are the system, default, and logsegment segments.

Type the following into a file segmap.sql: 

use master
go
if exists (select * from sysobjects
                where name = 'sp_segmap')
  drop procedure sp_segmap
go
create procedure sp_segmap
@segmap int
as
create table #seg
      (segment_num int NULL)
declare @segnum int
declare @pattern int
select @segnum = 0
select @pattern = 1
if @segmap = 0
/* no segments mapped */ 
begin
  insert #seg values(NULL)
  select * from #seg
  order by segment_num
  return
end
while (@segnum < 30)
begin
  if (@segmap & @pattern) != 0
    insert #seg values(@segnum)
  select @pattern = @pattern * 2
  select @segnum = @segnum + 1
end

/* Test final bit in @pattern */ 

if (@segmap & @pattern) != 0
  insert #seg values(@segnum)

/* Test if segment 31 bit on */ 

if @segmap <= -1
  insert #seg values(31)

select * from #seg
order by segment_num
go

grant execute on sp_segmap to public
go

Run segmap.sql in isql as the sa user:

isql /Usa /P<password> /S<server> /e /isegmap.sql /osegmap.sql

Additional query words: segments Transact_SQL Windows NT 


Keywords          : kbprg SSrvAdmin SSrvWinNT 
Version           : 4.2 | 4.2
Platform          : OS/2 WINDOWS 
Issue type        :

Last Reviewed: March 17, 1999