Thursday, October 30, 2008

SQL*Loader Part #2

The Discard File

As SQL*Loader executes, it may create a file called the discard file. This file is created only when it is needed, and only if you have specified that a discard file should be enabled. The discard file contains records that were filtered out of the load because they did not match any record-selection criteria specified in the control file. The discard file therefore contains records that were not inserted into any table in the database. You can specify the maximum number of such records that the discard file can accept. Data written to any database table is not written to the discard file.

Log File and Logging Information

When SQL*Loader begins execution, it creates a log file. If it cannot create a log file, execution terminates. The log file contains a detailed summary of the load, including a description of any errors that occurred during the load.

Conventional Path Loads

During conventional path loads, the input records are parsed according to the field specifications, and each data field is copied to its corresponding bind array. When the bind array is full (or no more data is left to read), an array insert is executed. SQL*Loader stores LOB fields after a bind array insert is done. Thus, if there are any errors in processing the LOB field (for example, the LOBFILE could not be found), the LOB field is left empty. Note also that because LOB data is loaded after the array insert has been performed, BEFORE and AFTER row triggers may not work as expected for LOB columns. This is because the triggers fire before SQL*Loader has a chance to load the LOB contents into the column. For instance, suppose you are loading a LOB column, C1, with data and that you want a BEFORE row trigger to examine the contents of this LOB column and derive a value to be loaded for some other column, C2, based on its examination. This is not possible because the LOB contents will not have been loaded at the time the trigger fires.

Direct Path Loads

A direct path load parses the input records according to the field specifications, converts the input field data to the column datatype, and builds a column array. The column array is passed to a block formatter, which creates data blocks in Oracle database block format. The newly formatted database blocks are written directly to the database, bypassing much of the data processing that normally takes place. Direct path load is much faster than conventional path load, but entails several restrictions.

A parallel direct path load allows multiple direct path load sessions to concurrently load the same data segments (allows intrasegment parallelism). Parallel direct path is more restrictive than direct path.


Invoking SQL*Loader

When you invoke SQL*Loader, you can specify certain parameters to establish session characteristics. Parameters can be entered in any order, optionally separated by commas. You specify values for parameters, or in some cases, you can accept the default without entering a value. For example:

SQLLDR CONTROL=sample.ctl, LOG=sample.log, BAD=baz.bad, DATA=etc.dat
USERID=scott/tiger, ERRORS=999, LOAD=2000, DISCARD=toss.dsc, DISCARDMAX=5

If you invoke SQL*Loader without specifying any parameters, SQL*Loader displays a help screen similar to the following. It lists the available parameters and their default values.


Alternative Ways to Specify Parameters

If the length of the command line exceeds the size of the maximum command line on your system, you can put certain command-line parameters in the control file by using the OPTIONS clause. You can also group parameters together in a parameter file. You specify the name of this file on the command line using the PARFILE parameter when you invoke SQL*Loader.

Examples:

1. One can load data into an Oracle database by using the sqlldr utility. Invoke the utility as follows:

sqlldr username@server/password control=loader.ctl
sqlldr username/password@server control=loader.ctl

This sample control file (loader.ctl) will load an external data file containing delimited data:
-------------------------------------------------------------------------------------------------------------------------------------
load data
infile 'c:\data\mydata.csv'
into table emp
fields terminated by "," optionally enclosed by '"'
( empno, empname, sal, deptno )
-----------------------------------------------------------------------------------------------------------------------------------
The mydata.csv file may look like this:

10001,"Scott Tiger", 1000, 40
10002,"Frank Naude", 500, 20
-----------------------------------------------------------------------------------------------------------------------------------

2. Another Sample control file with in-line data formatted as fix length records. The trick is to specify "*" as the name of the data file, and use BEGINDATA to start the data section in the control file:
--------------------------------------------------------------------------------------------------------------------------------------
load data
infile *
replace
into table departments
( dept position (02:05) char(4),
deptname position (08:27) char(20)
)
begindata
COSC COMPUTER SCIENCE
ENGL ENGLISH LITERATURE
MATH MATHEMATICS
POLY POLITICAL SCIENCE
-------------------------------------------------------------------------------------------------------------------------------------

3. Data can be modified as it loads into the Oracle Database. One can also populate columns with static or derived values. However, this only applies for the conventional load path (and not for direct path loads). Here are some examples:
--------------------------------------------------------------------------------------------------------------------------------
LOAD DATA
INFILE *
INTO TABLE modified_data
( rec_no "my_db_sequence.nextval",
region CONSTANT '31',
time_loaded "to_char(SYSDATE, 'HH24:MI')",
data1 POSITION(1:5) ":data1/100",
data2 POSITION(6:15) "upper(:data2)",
data3 POSITION(16:22)"to_date(:data3, 'YYMMDD')"
)
BEGINDATA
11111AAAAAAAAAA991201
22222BBBBBBBBBB990112
--------------------------------------------------------------------------------------------------------------------------------------
LOAD DATA
INFILE 'mail_orders.txt'
BADFILE 'bad_orders.txt'
APPEND
INTO TABLE mailing_list
FIELDS TERMINATED BY ","
( addr,
city,
state,
zipcode,
mailing_addr "decode(:mailing_addr, null, :addr, :mailing_addr)",
mailing_city "decode(:mailing_city, null, :city, :mailing_city)",
mailing_state
)
------------------------------------------------------------------------------------------------------------------------------------

For more examples please go here :

Related Topic:
  1. SQL*Loader Part #1
  2. SQL*Loader Part #2
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