Conventional Path Load and Direct Path Load : Simple to use in complex situations

One of my seminar participant asked me about what actually happens at oracle data block level during direct path loading in comparison to conventional path uploading. Even I was eager to know when first time I got this question. I patiently told participant that I will find out root of this question. Here is my analysis.

A conventional path load executes SQL INSERT statements to populate tables in an Oracle database. A direct path load eliminates much of the Oracle database overhead by formatting Oracle data blocks and writing the data blocks directly to the database files.

A direct load does not compete with other users for database resources, so it can usually load data at near disk speed.

To start SQL*Loader in direct path load mode, set the DIRECT parameter to true on the command line or in the parameter file, if used, in the format:

DIRECT=true

By default, the loading method is Conventional.

The script, which creates the views used by the Direct Path, is: catldr.sql (OH\rdbms\admin)

(This script is run by catalog.sql, by default).

Conventional Path	Direct Path
SQL*Loader uses the SQL INSERT statement and bind array buffer to load data.	It passes on the data to the Load Engine of the database, which creates a Column Array structure.
Makes use of the Database buffer cache and may increase contention for the resources among other users.	Avoids buffer cache and writes directly to the Disk. Can make use of Asynchronous I/O if available/supported on the OS.
Slower since the SQL INSERT statements have to be generated, passed to Oracle, and executed.	Faster since, the Load Engine converts the column array structure directly to Oracle Data Blocks and adds it to the Table’s existing segment.
While loading the data, searches for blocks with enough free space, into which the rows can be inserted.	Does not search the existing blocks. New blocks are formatted and added to the existing segment.
Does not lock the table being loaded into.	Locks table in Exclusive mode. Hence, should not be used if concurrent access to the table is required during the load. The 10046 trace output shows: ‘Lock table <table_name> exclusive mode nowait;’
Can be used to load into Clustered tables	Cannot be used to load into a cluster.
Check constraints are enabled during the load. Records not satisfying the constraint are rejected and written into the BAD file.	The constraints are disabled during the load. It explicitly executes an ‘alter table <table_name> disable constraint <constraint_name>’ statement before loading into the table.
Can be used to load into Varrays	Cannot be used to load into Varrays
Can be used to load into BFILE columns.	Cannot be used to load into BFILE columns.
Can be used to load into a Single partition of a table having Global indexes	Direct path cannot be used to load into a particular partition of the table if the table has a global index defined on it.
Cannot be used for loading data in Parallel. But, you can use multiple load session concurrently inserting into the same table.	Parallel loading of data is possible.
Automatically inserts default values for the columns, if any.	The default value specified for the column is not inserted. If it is a ‘null’ column, it inserts a null.
Indexes
Unique Index on the table is in a valid state after the load. The uniqueness of the data for the index column is maintained. Records violating the uniqueness are rejected and written into the BAD file.	The Uniqueness of the data is not validated. The unique index is in an ‘UNUSABLE’ state at the end of the load.
If the table has any indexes, corresponding keys are added into the index for each new row inserted into the table.	After each block is formatted, the new index keys are put in a sort (temporary) segment. The old index and the new keys are merged at load finish time to create the new index.
The index does not require a re-build at the end of the load. Also, no extra storage is required. But, since the index is updates for each new row, it increases the processing time.	The index needs to be re-built at the end of the load. The old index, new index and sort segment all require storage space until the indexes are merged.
Loading into Objects
If the type has a User-defined constructor matching the arguments of the attribute-value constructor, conventional path calls the User-defined constructor.	Direct path calls the Argument-value constructor.
If the type has a User-defined constructor not matching the arguments of the attribute-value constructor, you can invoke the user-defined using an SQL Expression.	It is not possible to invoke the user-defined constructor in direct path loading.
Can be used to load into Parent and child table at the same time.	Cannot be used to load into Parent and child table at the same time