Creating a SQL Patch with Many Hints Requires a Hack
In the past, when I created a SQL patch, I always specified a small number of hints. Last week, for the first time, I created one with more than 100 of them. Given their number, I didn’t want to...
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Observations About the Scalability of Data Loads in Snowflake
In the last weeks, I was running a number of tests based on the TPC-DS benchmark against Snowflake. One of the first thing I did is of course to create the TPC-DS schema and populate it. The aim of...
View ArticleAWR: Multitenant-Specific Initialization Parameters
By default, the database engine automatically takes snapshots in the root container only. Such snapshots cover the root container as well as all open PDBs belonging to it. From version 12.2 onward, you...
View ArticleAWR Flush Levels
From version 12.1.0.2 onward, for taking AWR snapshots, you have the choice between four AWR flush levels: BESTFIT, LITE, TYPICAL and ALL. If you check the Oracle Database documentation, you won’t find...
View ArticleMIN/MAX Optimization and Asynchronous Global Index Maintenance
In this short post I would like to point out a non-obvious issue that one of my customers recently hit. On the one hand, it’s a typical case where the query optimizer generates a different (suboptimal)...
View ArticleV$SQL_CS_HISTOGRAMS: What Are the Buckets’ Thresholds?
The contents of the V$SQL_CS_HISTOGRAM view is used by the SQL engine to decide when a cursor is made bind aware, and therefore, when it should use adaptive cursor sharing. For each child cursor, the...
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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...
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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...
View ArticleDBMS_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...
View ArticlePartition-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...
View ArticleTKPROF’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...
View ArticleScripts 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. download18.cmd...
View ArticleCDB 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...
View ArticleHow 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...
View ArticlePurging 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...
View ArticleSQL_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...
View ArticleSPD State Does Not Change If Adaptive Statistics Are Disabled
The aim of this post is to point out an issue (bug?) that I recently discovered. But, before talking about it, I need to go through a rather long introduction about the state of SQL plan directive...
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The APPROX_MEDIAN Function – A Test Case
The aim of this post is not to explain how the APPROX_MEDIAN function works (you find basic information in the documentation) but to show you the results of a test case I ran to assess how well it...
View ArticleActivating and Deactivating Performance Feedback
Performance feedback is one of the adaptive query optimizer features introduced in Oracle Database 12c. The aim of this short post isn’t to explain how it works, but to simply warn you about a buggy...
View ArticleOffline Analysis of ASH Data with ASHDUMP
From time to time, it happens to me to carry out offline analyses of ASH data. For that, I mean to analyze the ASH data without having access to the database instance that generated it. For that...
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