Archives of the TeradataForum

Message Posted: Mon, 11 Jul 2011 @ 09:27:36 GMT

	<Prev	Next>		<<First	<Prev	Next>	Last>>

Hi Sukul,

Not sure how much detail you want, but what I'm reasonably certain happens is:

- after logon, FL creates the two error tables

- during "phase 1" FL transfers data rows from the client system directly into the target table, storing each data row on the correct AMP. During this phase the data is not accessible.

- after all the data is transferred, FL enters "phase 2" (this is triggered by the "End Loading" command in the FL script). During this phase the data rows are sorted (by rowhash ?) which puts the rows into the correct logical order and also removes any duplicate rows. (Note that FL cannot load duplicate rows - even into a multiset table).

- once phase 2 is complete, locks are released, error tables are dropped (if they are empty) and the target table is now accessible by regular sql requests.

Multiload is similar in some respects, but very different in others.

- after logon, ML creates the two error tables and a work table for each target table, and one restart log table

- during "acquisition phase" ML transfers data rows from the client system into the work table(s), storing each data row on the correct AMP. During this phase the data in the target table IS accessible. I think that this phase stores the data in the work table(s) in rowhash order (but not certain).

- after all the data is transferred, ML enters the "application phase". During this phase the target table is changed with rows being inserted, updated and/or deleted as required. Secondary indexes are then updated.

- once the Application Phase is complete, locks are released, work table(s) is/are dropped, error tables are dropped if they are empty, the restart log table is dropped if the job ran ok and the target table is now accessible by regular sql requests.

Yes, there are a couple of minor phases in between but that's the major elements to what happens.

Does that help ?

Cheers,

Dave

Ward Analytics Ltd - Information in motion (www.ward-analytics.com)

	<Prev	Next>		<<First	<Prev	Next>	Last>>