SQLLDR default character length & ways to fix it - oracle

Question

I faced with a situation where one the columns data to be uploaded exceeded 255 and it threw Error Field in data file exceeds maximum length error.
I found a way to fix it. Please find link here explaining the logic.
The question is that in a control file, is there any difference between
Comments CHAR(255) "TRIM(:Comments)" ,
and
Comments CHAR "TRIM(:Comments)" ,
when it comes to the internal workings of sqlldr or it means the same right ?
Also while uploading, because the integrity of the data file cannot be trusted, we create a table with all columns as 255 [which i will fix for columns > 255 length] and I never specify the CHAR length in the control file.
I would like to know if the difference between
using default 255 for all columns
vs
keeping little extra than expected length [actual target table column length values] eg. actual expected length [which might range from 10 to 150 etc.] + 50/100
is very significant if i use sqlldr atleast 2000 times a day on small data files with average of 250 records.
Thanks in advance for the clarification.

Answer 1

I think they are the same as internally that is what the buffer size is as well.
After dealing with this enough times I created a real rough utility script that generates a skeleton control file that uses the column's actual size. It gets me 90% of the way there and no column sizing issues. It may be better on memory as its not going to use the full 255 chars available if the column is smaller. Give it a try if you want. It may give you some ideas anyway.
/********************************************************************************************************
Name: GEN_CTL_FILE
Desc: Generates a skeleton control file for loading data via SQL*Loader.
Args: tablename_in IN VARCHAR2, delim_in IN VARCHAR2 DEFAULT '|'
Returns: None.
Usage: utilities.gen_ctl_file('tablename');
Notes: Prints a skeleton control file.
If a template for a fixed-length data file is desired, use 'FIXED' for the delim_in string.
FIXED needs more work to put actual lengths in. For now just placeholders.
Example usage:
set serveroutput on;
execute utilities.gen_ctl_file('test', utilities.TAB);
REVISIONS:
Ver Date Author Description
--------- ---------- --------------- ------------------------------------
1.1 6/6/2013 gary_w - Created procedure.
1.2 10/8/2013 gary_w - Fixed decode statement.
- Added option to generate a fixed-length template.
************************************************************************************************************************/
PROCEDURE GEN_CTL_FILE(tablename_in IN VARCHAR2, delim_in VARCHAR2 DEFAULT '|') IS
ERRNULLTABLENAME CONSTANT NUMBER := -20103; -- User-defined error numbers and messages.
ERRNULLTABLENAMEMSG CONSTANT VARCHAR2(100) := 'A table name is required.';
USAGE CONSTANT VARCHAR2(100) := '* USAGE: UTILITIES.GEN_CTL_FILE(tablename_in IN VARCHAR2, fieldsep_in VARCHAR2 DEFAULT ''|'')';
v_delim VARCHAR2(20) := NVL(delim_in, '|');
CURSOR COL_CUR IS
SELECT COLUMN_NAME,
DECODE(COLUMN_ID, 1, ' ', ',') || RPAD(COLUMN_NAME, 32) || case upper(v_delim)
when 'FIXED' then 'POSITION(99:99) '
else NULL
end|| DECODE(DATA_TYPE,
'VARCHAR2', 'CHAR('||DATA_LENGTH||') NULLIF(' || COLUMN_NAME || '=BLANKS)',
'FLOAT', 'DECIMAL EXTERNAL NULLIF(' || COLUMN_NAME || '=BLANKS)',
'NUMBER', DECODE( DATA_PRECISION,
0, 'INTEGER EXTERNAL NULLIF (' || COLUMN_NAME || '=BLANKS)',
DECODE(DATA_SCALE, 0, 'INTEGER EXTERNAL NULLIF (' || COLUMN_NAME || '=BLANKS)', 'DECIMAL EXTERNAL NULLIF (' || COLUMN_NAME || '=BLANKS)')),
'DATE', 'DATE "MM/DD/YYYY" NULLIF (' || COLUMN_NAME || '=BLANKS)',
data_type)
AS COL_DATA
FROM USER_TAB_COLUMNS
WHERE TABLE_NAME = UPPER(tablename_in)
ORDER BY COLUMN_ID;
BEGIN
IF tablename_in IS NULL THEN
RAISE_APPLICATION_ERROR(ERRNULLTABLENAME, ERRNULLTABLENAMEMSG || CR || USAGE);
END IF;
DBMS_OUTPUT.PUT_LINE('--');
DBMS_OUTPUT.PUT_LINE('-- NOTE - When using DIRECT=TRUE to perform block inserts to a table,');
DBMS_OUTPUT.PUT_LINE('-- the table''s triggers will not be used! Plan accordingly to');
DBMS_OUTPUT.PUT_LINE('-- manually perform the trigger actions after loading, if needed.');
DBMS_OUTPUT.PUT_LINE('--');
DBMS_OUTPUT.PUT_LINE('OPTIONS (DIRECT=TRUE)');
DBMS_OUTPUT.PUT_LINE('UNRECOVERABLE');
DBMS_OUTPUT.PUT_LINE('LOAD DATA');
DBMS_OUTPUT.PUT_LINE('APPEND');
DBMS_OUTPUT.PUT_LINE('INTO TABLE ' || UPPER(tablename_in));
DBMS_OUTPUT.PUT_LINE('EVALUATE CHECK_CONSTRAINTS');
if upper(v_delim) != 'FIXED' then
DBMS_OUTPUT.PUT_LINE('FIELDS TERMINATED BY ' || '''' || v_delim || '''');
DBMS_OUTPUT.PUT_LINE('OPTIONALLY ENCLOSED BY ''"'' ');
DBMS_OUTPUT.PUT_LINE('TRAILING NULLCOLS');
end if;
DBMS_OUTPUT.PUT_LINE('(');
-- The cursor for loop construct implicitly opens and closes the cursor.
FOR COL IN COL_CUR
LOOP
IF COL.COLUMN_NAME != 'LOAD_DATE' THEN
IF COL.COLUMN_NAME = 'LOAD_SEQ_ID' THEN
dbms_output.put_line(','||RPAD('LOAD_SEQ_ID', 32)||'CONSTANT 0');
ELSE
DBMS_OUTPUT.PUT_LINE(COL.COL_DATA);
END IF;
END IF;
END LOOP;
DBMS_OUTPUT.PUT_LINE(')' || CHR(10));
EXCEPTION
WHEN OTHERS THEN
RASIE;
END; -- GEN_CTL_FILE
The output looks like this:
--
-- NOTE - When using DIRECT=TRUE to perform block inserts to a table,
-- the table's triggers will not be used! Plan accordingly to
-- manually perform the trigger actions after loading, if needed.
--
OPTIONS (DIRECT=TRUE)
UNRECOVERABLE
LOAD DATA
APPEND
INTO TABLE TEST
EVALUATE CHECK_CONSTRAINTS
FIELDS TERMINATED BY '|'
OPTIONALLY ENCLOSED BY '"'
TRAILING NULLCOLS
(
COLA CHAR(200) NULLIF(COLA=BLANKS)
,COLB CHAR(100) NULLIF(COLB=BLANKS)
,COLC CHAR(500) NULLIF(COLC=BLANKS)
,COLD DECIMAL EXTERNAL NULLIF (COLD=BLANKS)
,COLE CLOB
)
If you tweak it, please share your changes.