Oracle 18c Download and New Feature Scalable Sequence..!!

ByJoel Pérez ( Oracle ACE Director )

Oracle 18c Download and New Feature Scalable Sequence..!!

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Oracle 18c Download and New Feature Scalable Sequence..!!

By Eygle Gai ( Oracle ACE Director )

Oracle 18c has released and is currently available for download in the Oracle Edelivery website:

Searching Oracle Database” in the site, You can see the software media of the 18th edition,The current declared media is Exadata only, but it should be possible to install on non-Exadata Linux system platforms. OEL is Oracle’s best recommended support platform:

The current media contains three major files, the clients, software and Grid installation package. The first version of the Linux system is supported (Baidu Cloud shares a copy of software. Search The keyword ’18cNF’ these Files can found in the directory):

We have noticed an interesting feature: Extensible Sequence – Scalable Sequence

By specifying the SCALE clause in a CREATE SEQUENCE or ALTER SEQUENCE statement, you can make the sequence robustly extensible.

How is this feature implemented? What is it to solve?

Let’s review a online lesson of Andrew Holdsworth, who is the Vice President of the Oracle RWP teamIn this video, Andrew mentioned the various index competitions encountered during optimization:

Now let’s take a look at the definition of the scalable sequence in 18c:

The scalable sequence is defined by the following syntax:

When the SCALE statement is specified, a 6-digit number is specified as the sequence prefix, followed by the normal sequence number, and these two number are combined into a new sequence:

How do we get the 6-digit prefix? It is generated by instance number and session number:

6 digit scalable sequence offset number = 3 digit instance offset number || 3 digit session offset number.
The 3 digit instance offset number is generated as [(instance id % 100) + 100]. The 3 digit session offset number is generated as [session id % 1000].

So, this design is exact the same as Andrew’s previous description, which is exactly the guidance from practice that ultimately promoted the progress of Oracle database products.

Lets do a little test:

drop sequence enmo_seq;


SELECT enmo_seq.nextval FROM dual;

Because there is a 6-bit prefix, the sequence must have a minimum length of 7 bits

Even with 7 bits, there will be only 9 available values for a single process connection:

ORA-64603: NEXTVAL cannot be instantiated for ENMO_SEQ. Widen the sequence by 1 digits or alter sequence with SCALE EXTEND.

through this sequential, data can be truly dispersed from different instances, and system has got the lower index competition, higher performance and scalable sequence as well.

Until here the article. Thanks for Reading!

We hope the content could be useful for your Oracle DBA Tasks!

This article is brought by Yunhe Enmo (Beijing) Technology Co.,LTD

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Joel Pérez is an Expert DBA ( Oracle ACE Director, Maximum Availability OCM, OCM Cloud Admin. & OCM12c/11g ) with over 17 years of Real World Experience in Oracle Technology, specialised in design and implement solutions of: High Availability, Disaster Recovery, Upgrades, Replication, Cloud and all area related to Oracle Databases. International consultant with duties, conferences & activities in more than 50 countries and countless clients around the world. Habitual and one of leading writers of Technical Oracle articles for: OTN Spanish, Portuguese, English and more. Regular Speaker in worldwide Oracle events like: OTN LAD (Latin America), OTN MENA (Middle East & Africa), OTN APAC ( Asian Pacific), DTCC China, Oracle Code.. . Joel has always been known for being a pioneer in Oracle technology since the early days of his career being the first Latin American awarded as “OTN Expert” at year 2003 by Oracle Corp., one of the first “Oracle ACE” globally in the Oracle ACE Program at year 2004. He was honoured as one of the first “OCM Database Cloud Administrator” & Maximum Availability OCM in the world. Currently Joel works as Senior Cloud Database Architect in “Yunhe Enmo (Beijing) Technology Co.,Ltd”., company located in Beijing, China

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