Comparision of Sort Stage and Order by clause

[Roopanwita]

Hi,
Can any one tell me why Order by clause gives better performance than Sort Stage of DataSatge. Basically how Sort Stage of DS works.

[ray.wurlod]

Define "performance" in an ETL context.

The ORDER BY clause is possibly helped by an index. B-tree indexes are already stored in sorted order.

DataStage has no such help.

[Roopanwita]

So having an index will improve performance. So SQL order by clause should give better performance than DS sort Stage. But in real scenario, in one of my job DS sort stage is performing better than Order by clause.So I just want to know how DS sort stage work internally(i.e. internanal processes involved in sorting)

[ray.wurlod]

That suggests that the ORDER BY column is not indexes.

No information is published on the sorting algorithm used by DataStage other than "it's faster than UNIX sort command".

I suspect it's a multi-threaded heap-merge sort, but can offer no proof.