RE: Three billion logical reads?

Thanks Toon, comments in-line below.
   
  
"Koppelaars, Toon" <T.Koppelaars@xxxxxxxxxxxxxxxxxxxx> wrote:
        v\:* {behavior:url(#default#VML);}  o\:* {behavior:url(#default#VML);}  
w\:* {behavior:url(#default#VML);}  .shape {behavior:url(#default#VML);}        
        David,
   
  Your formula assumes only one block access to each of the twelve other 
tables, in case of there being a matching record.
   
  DA: Yes.
   
  « outer joins against non-unique indexex »
  This means those twelve tables are all child-tables to the 80 million table?
   
  DA: No, just a badly designed/implemented CRM system :)
   
  So there can be more than one matching record? Then you need to account for 
the clustering factor too: and factor that in into your formula (currently 
assuming only one block access for matching record(s?)).
   
  DA: Actually that's true in one case, as two of joins are actually self-joins 
to the same 80 million row table, once to get potential parents (0 or 1 match) 
and once to get potential children (0 .. n matches). There may be a number of 
table block access required for the children but I'm looking more for a 
best-case scenario so i'm underestimating where there is doubt.
   
  « outer joined to many smaller tables »
  This sounds like the twelve tables are ?lookup? tables to the 80 million 
table? (i.e. the 80 million table is the child table, like in a star schema).
   
  DA: Yes, mostly thay are, sometimes they are not. 
   
  There is some contradiction here...
   
  Are there any predicates against those twelve other tables?
   
  DA: No.
   
  Could you give us the query?
   
  It's very simple in form, with no predicates and just outer joins. It's an 
extract from a CRM system as part of an out-of-the-box ETL process. The 
rojected columns do require table access and can't be read from the indexes, so 
where a record is founf a table access is required in all cases ...
   
  SELECT <column(s)  from each table>
  FROM
  80mill_row_tab a,
  80mill_row_tab b,
  80mill_row_tab c,
  smaller_tab01 d,
  ...
  smaller_tab10 x
  where
  a.par_col = b.id(+) and
  a.chi_col = c.id(+) and
  a.col3 = d.col and
  ...
  a.col10 = x.col(+)
   
  Toon
   
      
---------------------------------
  
  From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On 
Behalf Of David Aldridge
Sent: vrijdag 26 oktober 2007 13:45
To: oracle-l@xxxxxxxxxxxxx
Subject: Three billion logical reads?

   
    Part 1: If I have a table of 80 million records and I outer join that to 
twelve other tables, and the tables are accessed with nested loop outer joins 
against non-unique indexes having a blevel of 3, and if there is only a 50% 
(say) chance of there being a matching record in those tables, then is the 
number of logical reads to perform the join equal to something in the order of:

     

    80,000,000*12*(3+.5)

     

    ?

     

    In other words, around 3.3 billion logical reads? Or do I need more coffee 
this morning?

     

    Part 2: What would you say is a reasonable ballpark time for a logical 
read, on a decently equipped server with SAN storage? Millisecond? Less?

     

     

     

    Background: I'm stuck in version 9 with large tabes outer-joined to many 
smaller tables -- no inut join swapping and hence no (reasonably efficient) 
hash outer joins.

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