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A tribute to Natural Join

By Franck Pachot

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I know that lot of people are against the ANSI join syntax in Oracle. And this goes beyond the limits when talking about NATURAL JOIN. But I like them and use them quite often.

Masterclass – 1

A recent thread on the Oracle developer community database forum raised a fairly typical question with a little twist. The basic question is “why is this (very simple) query slow on one system when it’s much faster on another?” The little twist was that the original posting told use that “Streams Replication” was in place to replicate the data between the two systems.

The size of Oracle Home: from 9GB to 600MB

By Franck Pachot

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This is research only and totally unsupported. When building docker images to run Oracle Database in a container, we try to get the smallest image possible. One way is to remove some subdirectories that we know will not be used. For example, the patch history is not used anymore once we have the required version. The dbca templates can be removed as soon as we have created the database… In this post I take the opposite approach: run some workload on a normal Oracle Home, and keep only the files that were used.

I have Oracle Database 18c installed in /u00/app/oracle/product/18EE and it takes 9GB on my host:

[oracle@vmreforatun01 ~]$ du --human-readable --max-depth=1 $ORACLE_HOME | sort -h | tail -10
 
352M /u00/app/oracle/product/18EE/jdk
383M /u00/app/oracle/product/18EE/javavm
423M /u00/app/oracle/product/18EE/inventory

ORACLE_HOME with symbolic link and postupgrade_fixups

By Franck Pachot

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Here is a quick post you may google into if you got the following error when running postupgrade_fixups.sql after an upgrade:

ERROR - Cannot open the preupgrade_messages.properties file from the directory object preupgrade_dir
DECLARE
*
ERROR at line 1:
ORA-29283: invalid file operation
ORA-06512: at "SYS.DBMS_PREUP", line 3300
ORA-06512: at "SYS.UTL_FILE", line 536
ORA-29283: invalid file operation
ORA-06512: at "SYS.UTL_FILE", line 41
ORA-06512: at "SYS.UTL_FILE", line 478
ORA-06512: at "SYS.DBMS_PREUP", line 3260
ORA-06512: at "SYS.DBMS_PREUP", line 9739
ORA-06512: at line 11

18c runInstaller -silent

By Franck Pachot

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ATP vs ADW – the Autonomous Database lockdown profiles

By Franck Pachot

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The Oracle database has always distinguished two types of workloads: transactional (OLTP) and datawarehouse (VLDB, DWH, DSS, BI, analytics). There is the same idea in the managed Oracle Cloud with two autonomous database services.

To show how this is old, here is how they were defined in the Oracle7 Tuning Book:

CaptureOLTPvsDSS

The definition has not changed a lot. But the technology behind DSS/DWH has improved. Now, with In-Memory Column Store, Smart Scan, Result Cache we can even see that indexes, materialized views, star transformation, hints,.. are disabled in the Autonomous Datawarehouse cloud service.

MERGE JOIN CARTESIAN: a join method or a join type?

By Franck Pachot

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I’ll present about join methods at POUG and DOAG. I’ll show how the different join methods work in order to better understand them. The idea is to show Nested Loops, Hash Join, Sort Merge Join, Merge Join Cartesian on the same query. I’ll run a simple join between DEPT and EMP with the USE_NL, USE_HASH, USE_MERGE and USE_MERGE_CARTESIAN hints. I’ll show the execution plan, with SQL Monitoring in text mode. And I’ll put some gdb breakpoints on the ‘qer’ (query execution rowsource) functions to run the plan operations step by step. Then I’ll do the same on a different query in order to show in detail the 12c adaptive plans.

How much free space can be reclaimed from a segment?

By Franck Pachot

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You have the feeling that your table takes more blocks than it should? Here are the queries I use to quickly check the free space. The idea is to call DBMS_SPACE.SPACE_USAGE and infer the minimum space from the percentages. For example, a block in FS3 (defined as having at least 50 to 75% free space) is supposed to have at least 50% of free space. Of course it can have more, but you don’t know.

CQRS, Event Sourcing and the Oracle Database

By Franck Pachot

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This blog post relates my thoughts when reading about Command Query Responsibility Separation and Event Sourcing, in the context of the Oracle Database (but it can probably apply to any database). We see those terms in the new software architecture diagrams, but they are actually quite old:

Command-Query separation

Command-Query separation was defined by Bertrand Meyer 15 years ago, not for the database but for the Eiffel language. See page 22-44 of Eiffel: a language for software engineering.