Gather_table_stats with a method opt of "for all indexed columns size 0"

Question

I have 9 databases I support that contain the same structure, and very similar data concentrations. We are seeing inconsistent performance in the different databases due to bind variable peeking.. I have tracked it down to the Min and Max values that are gathered during the analyze. I analyze from one cluster, and export/import those statistics into the other clusters.. I then go about locking down the stats gathered. Some of the statistics are on tables that contain transient data (the older data is purged, and new data gets a new PK sequence number).
Since I am gathering statistics with a 'FOR ALL INDEXED COLUMNS SIZE 1', a min and max value are grabbed. This value is only appropriate for a short period of time, and only for a specific database. I do want oracle to know the density to help calculate, but I don't want cardinality based on whether the current bind values fall in this range..
Example
COLUMN PK
When I analyze the min is 1 and max is 5. I then let the database run, and the new min is 100 and max is 105.. same number of rows, but different min/max. At first a select * from table where pk>=1 and pk <=5 would return a cardinality of 5.. Later, a seelct * from tables where pk>=100 and pk<=105 would return a cardinaility 1.
Any ideas how to avoid this other than trying set min and max to something myself (like min =1 max = 99999999). ??

Answer 1

MarkDPowell wrote:
The Oracle documentation on bind variable peeking said it did not peek without histograms and I cannot remember ever seeing on 9.2 where the trace showed otherwise. Mark,
see this simple test case run on 9.2.0.8. No histograms, but bind variable peeking, as you can see that the EXPLAIN PLAN output generated by AUTOTRACE differs from the estimated cardinality of the actual plan used at runtime.
Which documentation do you refer to?
SQL>
SQL> alter session set nls_language = 'AMERICAN';
Session altered.
SQL>
SQL> drop table bind_peek_test;
Table dropped.
SQL>
SQL> create table bind_peek_test
  2  as
  3  select
  4             100 as n1
  5           , cast(dbms_random.string('a', 20) as varchar2(20)) as filler
  6  from
  7             dual
  8  connect by
  9             level <= 1000;
Table created.
SQL>
SQL> exec dbms_stats.gather_table_stats(null, 'bind_peek_test', method_opt=>'FOR ALL COLUMNS SIZE 1')
PL/SQL procedure successfully completed.
SQL>
SQL> variable n number
SQL>
SQL> variable n2 number
SQL>
SQL> alter system flush shared_pool;
System altered.
SQL>
SQL> exec :n := 1; :n2 := 50;
PL/SQL procedure successfully completed.
SQL>
SQL> set autotrace traceonly
SQL>
SQL> select * from bind_peek_test where n1 >= :n and n1 <= :n2;
no rows selected
Execution Plan
   0      SELECT STATEMENT Optimizer=CHOOSE (Cost=2 Card=1000 Bytes=24
          000)
   1    0   FILTER
   2    1     TABLE ACCESS (FULL) OF 'BIND_PEEK_TEST' (Cost=2 Card=100
          0 Bytes=24000)
Statistics
        236  recursive calls
          0  db block gets
         35  consistent gets
          0  physical reads
          0  redo size
        299  bytes sent via SQL*Net to client
        372  bytes received via SQL*Net from client
          1  SQL*Net roundtrips to/from client
          4  sorts (memory)
          0  sorts (disk)
          0  rows processed
SQL>
SQL> set autotrace off
SQL>
SQL> select
  2             cardinality
  3  from
  4             v$sql_plan
  5  where
  6             cardinality is not null
  7  and      hash_value in (
  8    select
  9            hash_value
10    from
11            v$sql
12    where
13            sql_text like 'select * from bind_peek_test%'
14    );
CARDINALITY
          1
SQL>
SQL> alter system flush shared_pool;
System altered.
SQL>
SQL> exec :n := 100; :n2 := 100;
PL/SQL procedure successfully completed.
SQL>
SQL> set autotrace traceonly
SQL>
SQL> select * from bind_peek_test where n1 >= :n and n1 <= :n2;
1000 rows selected.
Execution Plan
   0      SELECT STATEMENT Optimizer=CHOOSE (Cost=2 Card=1000 Bytes=24
          000)
   1    0   FILTER
   2    1     TABLE ACCESS (FULL) OF 'BIND_PEEK_TEST' (Cost=2 Card=100
          0 Bytes=24000)
Statistics
        236  recursive calls
          0  db block gets
        102  consistent gets
          0  physical reads
          0  redo size
      34435  bytes sent via SQL*Net to client
       1109  bytes received via SQL*Net from client
         68  SQL*Net roundtrips to/from client
          4  sorts (memory)
          0  sorts (disk)
       1000  rows processed
SQL>
SQL> set autotrace off
SQL>
SQL> select
  2             cardinality
  3  from
  4             v$sql_plan
  5  where
  6             cardinality is not null
  7  and      hash_value = (
  8    select
  9            hash_value
10    from
11            v$sql
12    where
13            sql_text like 'select * from bind_peek_test%'
14    );
CARDINALITY
       1000
SQL>
SQL> spool offRegards,
Randolf
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