Observations About the Scalability of Data Loads in ADWC

In the last days, I am running a number of tests based on the TPC-DS benchmark against Oracle’s Autonomous Data Warehouse Cloud service (ADWC). One of the first thing I did is of course to create the TPC-DS schema and populate it. The aim of this blog post is to share some observations related to the population step.

I started by generating the data with the tool provided by TPC-DS: dsdgen. With the following command, (more...)

Which Privileges Are Required to Use the ADWC Service Console?

The Autonomous Data Warehouse Cloud (ADWC) service provides a Service Console that can be used to monitor the service activity and to carry out a small number of administration tasks (e.g. changing some resource management rules).

The documentation specifically says to use the ADMIN user to login. But, actually, any unlocked database user having the CREATE SESSION privilege can be used to login. This is not only useful, but, in my opinion, necessary. In (more...)

DBMS_CLOUD Package – A Reference Guide

The Appendix A of the Using Oracle Autonomous Data Warehouse Cloud guide describes the DBMS_CLOUD package. Unfortunately, it documents only a subset of the subroutines. And, for some of them, the description could also be enhanced. Therefore, while I was testing all the subroutines the DBMS_CLOUD package provides, I took a number of notes. By the end of my tests, I got what I can call my personal reference guide to the package. Since it (more...)

Partition-Wise Operations – New Features in 12c and 18c

Partition-wise operations are not something new. I do not remember when they were introduced, but at that time the release number was still a single digit. Anyway, the aim of this post is not to describe the basics, but only to describe what is new in that area in 12c and 18c.

The new features can be grouped in three categories:

  • Partition-wise GROUP BY enhancements available as of version 12.2
  • Partition-wise DISTINCT enhancements available (more...)

TKPROF’s Argument PDBTRACE

If you run TKPROF without arguments, you get a complete list of its arguments with a short description for each of them (here the output generated by version 18.1.0):

$ tkprof
Usage: tkprof tracefile outputfile [explain= ] [table= ]
              [print= ] [insert= ] [sys= ] [sort= ]
  table=schema.tablename   Use 'schema.tablename' with 'explain=' option.
  explain=user/password    Connect to ORACLE and issue EXPLAIN PLAN.
  print=integer    List only the first 'integer' SQL statements.
  pdbtrace=user/password   Connect  (more...)

Scripts to Download Oracle Database 18c Documentation

In the past I already shared with you the scripts I use to download the Oracle Database documentation. The aim of this short post is to reference the scripts I just wrote for 18c.

Happy downloading as well as happy reading!

PS: I also refreshed the scripts for 12.1 and 12.2.

CDB Views and Query Optimizer Cardinality Estimations

Today I faced a performance problem caused by a bad cardinality estimation involving a CDB view in a 12.1.0.2 multitenant environment. While solving the problem I did a number of observations that I try to summarize in this blog post.

First of all, when checking the execution plan of a query already running for more than two hours, I noticed that, in the execution plan, neither the referenced CDB view nor one (more...)

How Well a Query Optimizer Handles Subqueries?

At the beginning of December, at the UKOUG Tech17 conference in Birmingham (GB), I presented a comparison of the query optimizers of MySQL 8.0.3 and PostgreSQL 10.1. One of the things I talked about is their ability to handle subqueries. I summarized my findings with the following sentence:

Simple sub-queries that are not correctly optimized were observed.

It goes without saying that such a sentence leaves a lot of questions open. After (more...)

Purging Unused Triples Is a Never-ending Operation

This is a short post to point out a problem I recently discovered and for which I couldn’t find information online. Hence, in case you hit it, thanks to this short post I hope that you’ll save some time.

The documentation describes a procedure you can use to get rid of dangling triples stored in a semantic network. Simply put, you must execute a PL/SQL block like the following:

BEGIN
  sem_apis.purge_unused_values(flags => 'PARALLEL');
END;

(more...)

SQL_ADAPTIVE_PLAN_RESOLVED Is Broken

You can use the V$SQL.IS_RESOLVED_ADAPTIVE_PLAN column to know whether the execution plan associated to a child cursor is adaptive or not. Specifically, to know whether the query optimizer selected either an adaptive join method or an adaptive star transformation (notice that it is not set when the hybrid hash distribution is involved).

The column takes one of the following values:

  • NULL: the execution plan associated to the cursor is not adaptive
  • N: (more...)