Design Tips for Query Rewrite
Although Query Rewrite on Materialized Views is a powerful feature which is available in Oracle databases for a long time, it is rarely used. Many developers and database administrators don’t know about it or do not use it because they think it is too complex….
Data Vault Queries and Join Elimination
If you work with Data Vault for a data warehouse running in an Oracle database, I strongly recommend to use Oracle 12.2 or higher. Why that? Since Oracle 12c Release 2, join elimination works for more than one join column. This is essential for queries…
Constants vs. Parameterless Functions
Do you use parameterless PL/SQL functions in your queries? Did you know that this may cause performance issues? In this blog post I explain why parameterless functions can be the reason for bad execution plans in any Oracle Database. I recently had to analyze this…
Integrate SQL*Plus Scripts in SQL Developer
I envy my DBA colleagues when they work with the Oracle Database from the command line in an incredibly efficient way. They just call a series of scripts with some parameters to get the desired information. Everything looks so easy, so smooth, so natural. I’m…
Partition Pruning and NLS Settings
NLS (National Language Support) parameters are very useful for multilingual applications in an Oracle database. But it is important to understand their impact on query performance. I was aware that NLS is important for indexes, but never thought about its impact on partitioning. In a…
Bitmap-based COUNT(DISTINCT) Functions in Oracle 19c
Oracle 19c provides a set of new SQL functions for bitmap operations. They allow fast computation of COUNT(DISTINCT) expressions. What is the purpose of these functions? The Oracle documentation is very sparse, but at least it tells us that the main focus are Materialized Views on…
Materialized View Refresh for Dummies
Materialized Views are often used in data warehouses to improve query performance on aggregated data. But what if it takes too long to refresh the materialized views? Here are some basic rules to improve refresh performance. Unlike indexes, materialized views are not automatically updated with…
MemOptimized RowStore in Oracle Database 19c
Since February, 13 2019 Oracle Database 19c is available. I blogged about this feature here and here. Time for an update. So, what’s new in 19c regarding the MemOptimized Rowstore? Fast Lookup Works with JDBC Thin Driver I listed 16 prerequisites for the MemOptimized Rowstore in this…
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….
ORA-22905 when calling ODCI Table functions from PL/SQL
Back in 2015 I experimented using ODCITable* functions to dynamically parse delimited text (see blog post here.) Now blog reader Daniel Cabanillas points out, that it raises an error when used in PL/SQL. Silly me – I had only tried it out in SQL (my…
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