提高每个账户查询三条最近记录的保存性能

我在Oracle(10gXE)数据库中有一个表,我将清理它,并且只保留每个帐户的三个最近记录。我现在正在做的是:

CREATE TABLE ACCOUNT_TRANSACTION_TMP NOLOGGING AS SELECT * FROM ACCOUNT_TRANSACTION WHERE 1=2;


DECLARE
    CURSOR mbsacc_cur (account_id_var account_transaction.account_id%TYPE) IS
        SELECT * FROM account_transaction WHERE account_id = account_id_var ORDER BY transaction_time DESC;

    account_transaction_rec account_transaction%ROWTYPE;
BEGIN
    FOR i IN (SELECT DISTINCT(account_id) FROM account_transaction) LOOP
        OPEN mbsacc_cur(i.account_id);
        LOOP
            FETCH mbsacc_cur INTO account_transaction_rec;
            EXIT WHEN mbsacc_cur%NOTFOUND OR mbsacc_cur%ROWCOUNT > 3;
            INSERT /*+ append */ INTO account_transaction_tmp VALUES account_transaction_rec;
        END LOOP;
        CLOSE mbsacc_cur;
    END LOOP;
END;
/

然后我将删除旧表,将新表重命名为旧表,并添加约束。

但问题是,上述代码将永远运行(约3-4小时),保持大约100万条记录,其中大约一半应该被删除。

有什么方法可以提高这方面的性能吗?