Since SQL Server 2014, Tables with Columnstore Index are no longer read only and are updatable. This post is only applicable to SQL Server 2012.
Columnstore Index on fact tables provide significant improvements in response time especially for aggregated queries. One of the first things I did after migrating my databases to SQL Server 2012 was to create Columnstore Index on fact tables. Now I can run aggregated queries that fetch results in reasonable response a time which is great for development, unit testing and helps testers to run their test scripts faster.
One caveat to be aware of is that the table on which a Columnstore Index is defined cannot be inserted, updated or deleted (at the time of writing this post). Continue Reading
Late Arriving Dimension/Early Arriving Fact as the name implies is a dimension record which is not available when the ETL loads the related fact record but becomes available at a later time.
This scenario could happen for a variety of reasons;
- It might be a perfectly valid business process. For e.g. in an emergency ward, the patient interventions could be recorded first as priority while the patient details that is collected could be recorded into the system at a later time.
- Sometimes due to operational reasons, the data might arrive at different times from their respective source systems. For e.g. The dimensions could be extracted from Master Data repository while the facts are extracted directly from the transaction system at different periods.
- It might be due a failed ETL run.