Question

I have a procedure to find the first, last, max and min prices for a series of transactions in a very large table which is organized by date, object name, and a code. I also need the sum of quantities transacted. There are about 3 billion rows in the table and this procedure takes many days to run. I would like to cut that time down as much as possible. I have an index on the distinct fields in the trans table, and looking at the explain plan on the select portion of the queries, the index is being used. I am open to suggestions on an alternate approach. I use Oracle 11g R2. Thank you.

    declare
    cursor c_iter is select distinct dt, obj, cd from trans;
    r_iter c_iter%ROWTYPE;
    v_fir number(15,8);
    v_las number(15,8);
    v_max number(15,8);
    v_min number(15,8);
    v_tot number;
    begin
    open c_iter;
    loop
        fetch c_iter into r_iter;
        exit when c_iter%NOTFOUND;

      select max(fir), max(las) into v_fir, v_las 
      from 
            ( select 
                first_value(prc) over (order by seq) as "FIR",
                first_value(prc) over (order by seq desc) as "LAS"
              from trans
              where dt = r_iter.DT and obj = r_iter.OBJ and cd = r_iter.CD );

            select max(prc), min(prc), sum(qty) into v_max, v_min, v_tot
            from trans
            where dt = r_iter.DT and obj = r_iter.OBJ and cd = r_iter.CD;

            insert into stats (obj, dt, cd, fir, las, max, min, tot )
            values (r_iter.OBJ, r_iter.DT, r_iter.CD, v_fir, v_las, v_max, v_min, v_tot);

            commit;
    end loop;
    close c_iter;
end;

Answer 1

alter session enable parallel dml;

insert /*+ append parallel(stats)*/
into stats(obj, dt, cd, fir, las, max, min, tot)
select /*+ parallel(trans) */ obj, dt, cd
    ,max(prc) keep (dense_rank first order by seq) fir
    ,max(prc) keep (dense_rank first order by seq desc) las
    ,max(prc) max, min(prc) min, sum(qty) tot
from trans
group by obj, dt, cd;

commit;

• A single SQL statement is usually significantly faster than multiple SQL statements. They sometimes require more resources, like more temporary tablespace, but your distinct cursor is probably already sorting the entire table on disk anyway.
• You may want to also enable parallel DML and parallel query, although depending on your object and system settings this may already be happening. (And it may not necessarily be a good thing, depending on your resources, but it usually helps large queries.)
• Parallel write and APPEND should improve performance if the SQL writes a lot of data, but it also means that the new table will not be recoverable until the next backup. (Parallel DML will automatically use direct path writes, but I usually include APPEND anyway just in case the parallelism doesn’t work correctly.)

There’s a lot to consider, even for such a small query, but this is where I’d start.