Re: measure hidden free memory

[Saibabu Devabhaktuni <saibabu_d@xxxxxxxxx>]

"I have recently problems with a DB where the
permanent memory went up to 185m 
due to heavy fragmentation"

I guess "permanent mem" in x$ksmsp never grows unless
SGA is resized dynamically.

"Can we make the assumption that the part of free
memory hidden into the 
permanent memory is equal to the value reported in
v$SGASTAT - value reported 
into X$KSMSP ?"

The "free memory" reported in v$sgastat is the correct
value, which includes "free memory" from x$ksmsp and
the free memory hidden into the "permanent mem".
Oracle would release free memory from "permanent mem"
as the memory pressure increases.

Thanks,
 Sai.
http://sai-oracle.blogspot.com


just to check the validity of a theory :
 
 I have recently problems with a DB where the
permanent memory went up to 185m 
due to heavy fragmentation :
 
 sums taken from x$ksmsp excluding ksmchon like 'R-%'
:
 
 CONTENTS                           CHUNKS RECREATABLE
  FREEABLE      TOTAL
 ------------------------------ ---------- -----------
---------- ----------
 sql area                            11975      614856
  10337272   10952128
 library cache                        8240     1511400
   3245888    4757288
 free memory                         11637            
             16522128
 permanent memor                     29040            
            183711904
 .
 .
 .
 
 An alter system flush shared poll has no effect on
the fragmentation of the 
free memory we were forced to rebounce the DB in order
to reclaim these 29040 
chunks of free memory for a total of 184 meg.
 
 Just after the reboot we got the following figures :
 
 
 CONTENTS                           CHUNKS RECREATABLE
  FREEABLE      TOTAL
 ------------------------------ ---------- -----------
---------- ----------
 sql area                              671      403296
   1293944    1697240
 library cache                        1975      424880
    852464    1277344
 free memory                           219            
            251236016
 permanent memor                         4            
             47272080
 
 
 These figures are taken from x$ksms. at the same time
v$sgastat show for free 
memory :
 
 
 Pool         Name                                    
 BYTES
 ------------ ------------------------------
----------------
 buffer_cache                                    
385,875,968
 fixed_sga                                           
742,864
 java pool    free memory                         
83,886,080
 large pool   free memory                         
16,777,216
 log_buffer                                          
787,456
 shared pool  free memory                        
277,666,888
              miscellaneous                       
13,269,208
              dictionary cache                     
4,274,432
              library cache                        
3,945,616
 
 So V$SGASTAT show a free memory of 277 m and X$KSMSP
show 251 m.
 
 So here is my question : 
 
 Can we make the assumption that the part of free
memory hidden into the 
permanent memory is equal to the value reported in
v$SGASTAT - value reported 
into X$KSMSP ?
 
 
 In SQL :
 
 select fa-fb hidden_mem from
           (select 
                /* SGASTAT */sum(ksmsslen)/1048576 fa 
            from x\$ksmss 
            where  
                  ksmssnam='free memory' and 
                  ksmsslen > 1 group by ksmssnam),
           (select 
                /* X$KSMSP */ sum(ksmchsiz)/1048576 fb

            from sys.x\$ksmsp 
            where 
                  ksmchcom = 'free memory'      and 
                  inst_id = userenv('Instance') and 
                  ksmchcls not like 'R%' 
            group by ksmchcom)
 
 
 B. Polarski
 http://www.smenu.org

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