Scheduled Job to gather stats for multiple tables - Oracle 11.2.0.1.0

Question

Hi,
My Oracle DB Version is:
BANNER Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
PL/SQL Release 11.2.0.1.0 - Production
CORE 11.2.0.1.0 Production
TNS for Linux: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production
In our application, we have users uploading files resulting in insert of records into a table. file could contain records ranging from 10000 to 1 million records.
I have written a procedure to bulk insert these records into this table using limit clause. After the insert, i noticed my queries run slow against these tables if huge files are uploaded simultaneously. After gathering stats, the cost reduces and the queries executed faster.
We have 2 such tables which grow based on user file uploads. I would like to schedule a job to gather stats during a non peak hour apart from the nightly automated oracle job for these two tables.
Is there a better way to do this?
I plan to execute the below procedure as a scheduled job using DBMS_SCHEDULER.
--Procedure
create or replace
PROCEDURE p_manual_gather_table_stats AS
TYPE ttab
IS
    TABLE OF VARCHAR2(30) INDEX BY PLS_INTEGER;
    ltab ttab;
BEGIN
    ltab(1) := 'TAB1';
    ltab(2) := 'TAB2';
    FOR i IN ltab.first .. ltab.last
    LOOP
        dbms_stats.gather_table_stats(ownname => USER, tabname => ltab(i) , estimate_percent => dbms_stats.auto_sample_size,
        method_opt => 'for all indexed columns size auto', degree =>
        dbms_stats.auto_degree ,CASCADE => TRUE );
    END LOOP;
END p_manual_gather_table_stats;
--Scheduled Job
BEGIN
    -- Job defined entirely by the CREATE JOB procedure.
    DBMS_SCHEDULER.create_job ( job_name => 'MANUAL_GATHER_TABLE_STATS',
    job_type => 'PLSQL_BLOCK',
    job_action => 'BEGIN p_manual_gather_table_stats; END;',
    start_date => SYSTIMESTAMP,
    repeat_interval => 'FREQ=DAILY; BYHOUR=12;BYMINUTE=45;BYSECOND=0',
    end_date => NULL,
    enabled => TRUE,
    comments => 'Job to manually gather stats for tables: TAB1,TAB2. Runs at 12:45 Daily.');
END;Thanks,
Somiya

Answer 1

The question was, is there a better way, and you partly answered it.
Somiya, you have to be sure the queries have appropriate statistics when the queries are being run. In addition, if the queries are being run while data is being loaded, that is going to slow things down regardless, for several possible reasons, such as resource contention, inappropriate statistics, and having to maintain a read consistent view for each query.
The default collection job decides for each table based on changes it perceives in the data. You probably don't want the default collection job to deal with those tables. You probably do want to do what Dan suggested with the statistics. But it's hard to tell from your description. Is the data volume and distribution volatile? You surely want representative statistics available when each query is started. You may want to use all the plan stability features available to tell the optimizer to do the right thing (see for example http://jonathanlewis.wordpress.com/2011/01/12/fake-baselines/ ). You may want to just give up and use dynamic sampling, I don't know, entire books, blogs and papers have been written on the subject. It's sufficiently advanced technology to appear as magic.