Category Archives: ETL

Temporal Joins with SQL Macros in Oracle 20c

In a previous post on SQL macros in Oracle Database 20c we saw how SQL macros can be used to create a kind of “parameterized” views to establish a simplified access tier to temporal data. In this post I’d like to explore more possibilities to hide the complexity of SQL statements behind a functional syntax provided by using SQL macros. As an example we’ll stay with a temporal data introduced in the previous post and explore how we can do a temporal join of this versioned data.

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Issue with the Hint ENABLE_PARALLEL_DML

Performing an ETL with large data sets, it is often a good idea to run DML in parallel. But, in contrast to parallel query or DDL, parallel DML have to be explicitly enabled. You had to issue ALTER SESSION ENABLE PARALLEL DML in the past. Starting with 12c you can enable parallel DML specifically for each query using the hint ENABLE_PARALLEL_DML. For a few years now, I’ve been using the hint now and then and was quite happy. An observation I made a few days ago can lead to a rethinking. What I could observe is that for the SQL with embedded hint a new child cursor was created each time. Let’s test it!

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Online Statistics Gathering for ETL – Part 3

Preparing my session on Online Statistics Gathering for ETL for the DOAG conference, I noticed some points that I didn’t covered in the previous two blog posts. The first point is showing the problem that may arise if indexes are involved. The second one is about partition exchange load and it completes the topic of partitioned tables started in part 2. No blog posting on Oracle products is nowadays complete without mentioning the cloud. The third point is about Autonomous Data Warehouse Cloud Service and Online Statistics Gathering improvements. Continue reading