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July 2018

Complex materialized views and fast refresh

Just a quick discovery that came across the AskTOM “desk” recently. We have an outstanding bug in some instances of fast refresh materialized views when the definition of the materialized view references a standard view.

Here’s a simple demo of the issue – I’ll use a simplified version of the EMP and DEPT tables, linked by a foreign key in the usual way:

Index Column Order – Impact On Index Branch Blocks Part II (The Weeping Song)

In Part I, I discussed how the order of columns in an index makes no real difference to the effectiveness of the index if all columns are referenced via equality predicates. If the leading column has a high number of distinct columns, it might result in less necessary data within index branches as less data […]

I Got Here On My Own

Click bait worthy title, eh? </p />
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18c: some optimization about redo size

Some years ago, at the time of 12.1 release, I published in the SOUG newsletter some tests to show the amount of redo generated by different operations on a 10000 rows table. I had run it on 12.2 without seeing the differences and now on 18.1
I get the statistics from mystat using a script that displays them as columns, with the value being the difference from the previous run. I’ve run the same as in the article, and most of the statistics were in the same ballpark.

Standard Edition–different optimizer but still cool

One cool technique that the optimizer can employ is the BITMAP CONVERSION TO ROWIDS method to take advantage of B-tree indexes in a means that we would normally associate with a bitmap index. This can be particularly useful with multiple predicates on individually indexed columns because it lets us establish the rows of interest before having to visit the heap blocks.  Here’s an example of that in action, even when the indexes in question are Text indexes.

Enterprise Edition plan

Announcement: New Europe Seminar in Brussels, Belgium 27-28 September 2018

Due to popular demand, I’ll be running another of my acclaimed seminars in Europe later in the year, this time in Brussels, Belgium on 27-28 September 2018. This is a must attend seminar of benefit to not only DBAs, but also to Developers, Solution Architects and anyone else interested in designing, developing or maintaining high […]

Event Sourcing: CQN is not a replacement for CDC

We are in an era where software architects want to stream the transactions out of the database and distribute them, as events, to multiple microservices. Don’t ask why, but that’s the trend: store inconsistent eventually consistent copies of data in different physical components, rather than simply using logical views in the same database, where the data is ACIDely stored, processed and protected. Because it was decided that this segregation, in CQRS (Command Query Responsibility Segregation), will be physical, on different systems, the need for logical replication and change data capture is raising, with a new name: Event Sourcing.

Automation and Analytics

They say the devil is in the details and as I come from the DevOps side of the house, it would only be natural that I’d be attracted to how Microsoft Flow works with Power BI.  For those that aren’t familiar with Microsoft Flow, think of it like If This Then That, (IFTTT) from Microsoft.

I used IFTTT to automate a number of tasks at my previous company-  everything from posting to social media automation, notifications on Slack, creating weekly status reports and other tedious tasks that I hated having to do manually.

Clustering_Factor

Here’s another little note on the clustering_factor for an index and the table preference table_cached_blocks that can be set with a call to dbms_stats.set_table_prefs(). I might be repeating a point that someone made in a comment on an older posting but if that’s the case I can’t find the comment at present, and it’s worth its own posting anyway.