Oracle

At the end of the previous post on index hints I mentioned that I had been prompted to complete a draft from a few years back because I’d been sent an email by Kaley Crum showing the optimizer ignoring an index_rs_asc() hint in a very simple query. Here, with some cosmetic changes, is the example he sent me.

I’ve lost count of the number of times I’ve reminded people that hinting (correctly) is hard. Even the humble /*+ index() */ hint and its close relatives are open to misunderstanding and accidental misuse, leading to complaints that “Oracle is ignoring my hint”.

Strange though it may seem, I’m still not 100% certain of what some of the basic index hints are supposed to do, and even the “hint report” in the most recent versions of dbms_xplan.display_xxx() hasn’t told me everything I’d like to know. So if you think you know all about hints and indexing this blog note is for you.

I’ll start with a brief, and approximate, timeline for the basic index hints – starting from 8.0

In today’s video we’ll quickly demonstrate long identifiers, introduced in Oracle database 12.2.

The video is based on this article.

This is just a quick blog post to inform readers that SLOB 2.5.3 is now available at the following webpage: click here.

SLOB 2.5.3 is a bug fix release. One of the fixed bugs has to do with how SLOB sessions get connected to RAC instances. SLOB users can surely connect to the SCAN service but for more repeatable testing I advise SLOB 2.5.3 and SQL*Net services configured one per RAC node. This manner of connectivity establishes affinity between schemas and RAC nodes. For example, repeatability is improved if sessions performing SLOB Operations against, say, user7’s schema, it is beneficial to do so connected to the same RAC node as you iterate through your testing.

The following is cut and pasted from SLOB/misc/sql_net/README:

In my previous post in this series, I discussed out Automatic Indexing currently does not consider Non-Equality predicates. Automatic Indexing will index columns based only on Equality predicates. So how does Oracle handle the scenario when an SQL has a mixture of both Equality and Non-Equality predicates? I’ll begin by creating two very similar tables, […]

VirtualBox 6.1.18 has been released.

The downloads and changelog are in the usual places.

I’ve installed it on Windows 10, macOS Big Sur and Oracle Linux 7 hosts with no problems.

I’ll be running new Packer builds for the oraclebase/oracle-7 and oraclebase/oracle-8 vagrant boxes, so they should appear with the new version of the guest additions over the next day or so.

Cheers

Tim…

Links:

This is a list of possible explanations of errors that you might see in the Hint Report section of an execution plan. It’s just a list of the strings extracted from a chunk of the 19.3 executable around the area where I found something I knew could be reported, so it may have some errors and omissions – but there are plenty of things there that might give you some idea why (in earlier versions of Oracle) you might have seen Oracle “ignoring” a hint:

A little case study based on an example just in on the Oracle-L list server. This was supplied with a complete, working, test case that was small enough to understand and explain very quickly.

The user created a table, and used calls to dbms_stats to fake some statistics into place. Here, with a little cosmetic editing, is the code they supplied.

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The January Oracle quarterly patches were released yesterday, which prompted me to do some new builds.

We got Oracle REST Data Services (ORDS) 20.4 and SQLcl 20.4, which I use in a number of my Vagrant and Docker builds, so I updated them and ran some builds.

The Vagrant database builds, which include ORDS, can be found here.

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A few days ago Oracle announced the APEX Application Development Service on Oracle Cloud.