Tuesday, August 19, 2014

Zone Map Zone ID's

Just a quick follow up to my previous post on how Zone ID's are calculated.

Let's take the following example:
SQL> select rid, sys_op_zone_id(rid) zone_id
  2   from
  3   (
  4    select chartorowid('AAAS5KAAHAAABYDAAA') rid
  5     from dual
  6   );
 
RID                     ZONE_ID
------------------ ------------
AAAS5KAAHAAABYDAAA 324580438021

Recalling that extended ROWID has the following format (a nice picture from Oracle Documentation):



In the binary format that would correspond to:
  • Data Object Number -- 32 bits
  • Relative File Number -- 10 bits
  • Block Number -- 22 bits
  • Row Number -- 16 bits
We know that Row Number is irrelevant for the Zone Maps because they deal with block ranges. With that in mind a simple conversion to a (base 10) number would be:

(Block Number) + (Relative File Number) * 2 ^ 22 + (Data Object Number) * 2 ^ 32

Applying the above formula to our ROWID:
SQL> select
  2    dbms_rowid.rowid_block_number(rid) +
  3    dbms_rowid.rowid_relative_fno(rid) * power(2,22) +
  4    dbms_rowid.rowid_object(rid) * power(2,32) base_10
  5   from
  6   (
  7    select chartorowid('AAAS5KAAHAAABYDAAA') rid
  8     from dual
  9   );
 
        BASE_10
---------------
332370368534019

What's left after that is to slice the number into Zone Map chunk size (2^10 by default, thanks to Timur for pointing that out in the comments sections for the previous post):
SQL> select
  2    trunc((
  3    dbms_rowid.rowid_block_number(rid) +
  4    dbms_rowid.rowid_relative_fno(rid) * power(2,22) +
  5    dbms_rowid.rowid_object(rid) * power(2,32)
  6    )/power(2,10)) zone_id,
  7    sys_op_zone_id(rid) sys_zone_id
  8   from
  9   (
 10    select chartorowid('AAAS5KAAHAAABYDAAA') rid
 11     from dual
 12   );
 
     ZONE_ID  SYS_ZONE_ID
------------ ------------
324580438021 324580438021

That's all there is to it!

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