Как идентифицировать горячие блоки при cache buffer chains латчах :

note 163424.1

SQL> select CHILD#  "cCHILD"
    ,      ADDR    "sADDR"
    ,      GETS    "sGETS"
    ,      MISSES  "sMISSES"
    ,      SLEEPS  "sSLEEPS"
    from v$latch_children
    where name = 'cache buffers chains'
    order by 5, 1, 2, 3;

Run the above query a few times to to establish the id(ADDR) that has the most
consistent amount of sleeps. Once the id(ADDR) with the highest sleep count is found
then this latch address can be used to get more details about the blocks
currently in the buffer cache protected by this latch.
The query below should be run just after determining the ADDR with
the highest sleep count.

column segment_name format a35
    select /*+ RULE */
      e.owner ||'.'|| e.segment_name  segment_name,
      e.extent_id  extent#,
      x.dbablk - e.block_id + 1  block#,
      x.tch,
      l.child#
    from
      sys.v$latch_children  l,
      sys.x$bh  x,
      sys.dba_extents  e
    where
      x.hladdr  = '&ADDR' and
      e.file_id = x.file# and
      x.hladdr = l.addr and
      x.dbablk between e.block_id and e.block_id + e.blocks -1
    order by x.tch desc ;

Example of the output :
SEGMENT_NAME                     EXTENT#      BLOCK#       TCH    CHILD#
-------------------------------- ------------ ------------ ------ ----------
SCOTT.EMP_PK                       5            474          17     7,668
SCOTT.EMP                          1            449           2     7,668

И не большой солюшн:

Depending on the TCH column (The number of times the block is hit by a SQL
statement), you can identify a hotblock. The higher the value of the TCH column,
the more frequent the block is accessed by SQL statements.

In order to reduce contention for this object the following mechanisms can be put in place:

1) Examine the application to see if the execution of certain DML and SELECT statements
can be reorganized to eliminate contention on the object.

2) Decrease the buffer cache -although this may only help in a small amount of cases.

3) DBWR throughput may have a factor in this as well.
If using multiple DBWR's then increase the number of DBWR's.

4) Increase the PCTFREE for the table storage parameters via ALTER TABLE
or rebuild. This will result in less rows per block.

5) Consider implementing reverse key indexes
(if range scans aren't commonly used against the segment)