Data pump + statistics + dba_tab_modifications

Question

Database 11.2, persons involved with replicating data are using data pump and importing the statistics (that's all I know about their process). When I look at this query:
select /*mods.table_owner,
       mods.table_name,*/
       mods.inserts,
       mods.updates,
       mods.deletes,
       mods.timestamp,
       tabs.num_rows,
       tabs.table_lock,
       tabs.monitoring,
       tabs.sample_size,
       tabs.last_analyzed
from   sys.dba_tab_modifications mods join dba_tables tabs
       on mods.table_owner = tabs.owner and mods.table_name = tabs.table_name
where  mods.table_name = &tab;I see this:
INSERTS          UPDATES     DELETES     TIMESTAMP          NUM_ROWS     TABLE_LOCK     MONITORING     SAMPLE_SIZE     LAST_ANALYZED
119333320     0     0     11/22/2011 19:27     116022939     ENABLED          YES          116022939     10/24/2011 23:10As we can see, the source database last gathered stats on 10/24 and the data was loaded in the destination on 11/22.
The database is giving bad execution plans as indicated in previous thread: Re: Understanding results from dbms_xplan.display_cursor
My first inclination is to run the following, but since they imported the stats, should they already be "good" and it's a matter of dba_tab_modifications getting out of sync? What gives?
exec dbms_stats.gather_schema_stats(
     ownname          => 'SCHEMA_NAME',
     options          => 'GATHER AUTO'
   )

Answer 1

In your previous post you mentioned that the explain plan has 197 records. That is one big SQL statement, so the CBO has plenty of opportunity to mess it up.
That said, it is a good idea to verify that your statistics are fine. One way to accomplish that is to gather statistics into a pending area and compare the pending area stats with what is currently in the dictionary using DBMS_STATS.DIFF_TABLE_STATS_IN_PENDING.
As mentioned by Tubby in your previous post, extended stats are powerful and easy way to improve the quality of CBO’s plans. Note that in 11.2.0.2 you can create extended stats specifically tailored to your SQLs (based on AWR or from live system) - http://iiotzov.wordpress.com/2011/11/01/get-the-max-of-oracle-11gr2-right-from-the-start-create-relevant-extended-statistics-as-a-part-of-the-upgrade/
Iordan Iotzov
http://iiotzov.wordpress.com/
Edited by: Iordan Iotzov on Jan 6, 2012 12:45 PM