OOW 2019 - Significant Oracle Multitenant Announcements

Background

During Oracle OpenWorld 2019, there were significant announcements related to my favorite Oracle option in recent years - the Oracle Multitenant option. In this blog post I will summarize the highlights.

Oracle 19c Exciting News

Prior to Oracle 19c (Oracle 12c through 18c), in order to use pluggable databases (usually for consolidation purposes), one had to own the multitenant option which is an extra option (=cost) on top of the oracle enterprise edition. There was also a single-tenant option which allows running the multitenant architecture but with only one pluggable database; hence, single-tenant. You can read more about that in a blog post I wrote about Oracle's deployment options (Non-CDB, Single-Tenant, Multitenant).

Starting with Oracle 19c, customers can run 3 pluggable databases with no extra cost, i.e. without the multitenant license.

Oracle 20c - End of Era?

For years the non-cdb architecture has been defined officially by Oracle as deprecated and "may be desupported in the future". In OOW19, it was announced that the next Oracle release (20c) will be the first one that the non-cdb architecture will be officially desupported.

Oracle 19c - Automation and Manageability Enhancements

Introduction
DBAs should always aim to automate their tasks and avoid as much as possible manual repetitive tasks. This was always true; however, not always implemented; now with the new DevOps era, I see more and more Database teams who have been "hit" by the DevOps trend which demands more automation and collaboration in order to accelerate application updates & delivery

DBCA Silent Mode 
One of the common and popular ways to achieve automation when it comes to installation, configuration, and patching, is to leverage Oracle DBCA (Database Configuration Assistant) tool with the silent mode which is basically and alternative to the regular "GUI" mode DBCA.
When using silent mode, customers can run scripts that will handle a require operation without manual process which requires the "traditional" GUI mode.

Oracle 19c - Automation and Manageability Enhancements

The recent Oracle 19c release has introduced several interesting enhancements in the area of the DBCA silent mode. Now, the following operations can be used with the Silent mode:

• Ability to Create a Duplicate of an Oracle Database Using DBCA in Silent Mode
• Ability to Create a PDB by Cloning a Remote PDB Using DBCA in Silent Mode
• Ability to Relocate a PDB to Another CDB Using DBCA in Silent Mode

Oracle 19c New Features - Automatic flashback standby database when Primary database is flashed back

Prior to Oracle 19c, when using the "Flashback Database" feature on a primary database in a data guard environment would result in a standby database which is no longer in sync with the primary database; in previous releases, in order to ensure both primary and secondary are synced, then a manual procedure to flash back to standby database was required.

Starting with Oracle 19c, a standby database that is in a mounted state can automatically follow the primary database after a RESETLOGS operation on the primary. This simplifies standby management after a RESETLOGS operation on the primary.

This process is handled by the MRP (Managed Recovery Process) process that will automatically do the work for us.

For more information, see: https://docs.oracle.com/en/database/oracle/oracle-database/19/sbydb/managing-oracle-data-guard-physical-standby-databases.html#GUID-252097AC-3070-43B6-88D8-919AE27F97AD

Oracle 19c Privilege Analysis - Positive Licensing Update!

Introduction

One of the most valuable security related features which have been introduced recently (in Oracle 12c to be specific) is the Privilege Analysis feature. Using this feature, the DBA can easily understand which privileges are actually being used by users. Once the analysis has been completed, the DBA can revoke all of the unnecessary privileges/roles.
I actually wrote a dedicated blog post about this topic with some code examples. See: http://oracledbpro.blogspot.com/2015/12/oracle-12c-privilege-analysis.html

Oracle Database 19c Positive Licensing Update!
Prior to version 19c, this extremely helpful and useful feature was only available for Enterprise Edition with Oracle Database Vault (extra cost option).
Starting from 19c this feature is available with Enterprise Edition; in other words, no need for the data vault option which, is mentioned previously, is an extra cost option.

This is a really nice update from Oracle - let's hope that one day the Diagnostics & Tuning pack features (e.g. AWR, ADDM, ASH, etc.) will be included with the Enterprise Edition without forcing customers to buy the extra cost diagnostics & tuning packs options :)

Reference
https://docs.oracle.com/en/database/oracle/oracle-database/19/newft/new-features.html#GUID-57C5AD70-55F2-4E4E-879A-B2D88A237A24

Oracle RAC with Standard Edition (SE) 2 is not supported in 19c

Introduction
For so many years (starting in the early 2000's, when 10g was released) Oracle RAC option (Real Application Clusters) was available with Oracle Standard Editions; even when Oracle introduced Oracle Standard Edition 2 (SE2) back in version 12.1.0.2 (see my blog post about SE2 here), they offered the RAC option.

19c Update
With the introduction of the recent 19c release, Oracle did a pretty significant change with SE2 which I believe is worthy of a blog post.
Oracle RAC has been de-supported effective with Oracle Database 19c.
According to Oracle, "SE2 Socket requirements are hard to meet as hardware evolves." In addition, they claim that "SE Oracle RAC has seen diminishing demand with increased high availability requirements, as SE does not provide the full set of high availability capabilities available in the Oracle Database Enterprise Edition".

My Own View

I personally feel like Oracle licensing is too strict and with this recent change it became even stricter. For example, I always believed that Diagnostics and Tuning packs should have been part of the Enterprise Edition by default. I felt like the move to Standard Edition 2 back in 12.1.0.2 was strict as it was more limited than Standard Edition with the same price. I believe that the recent 19c SE2 change is a (valid) tactic to move people to Oracle cloud. The positive news is that from my experience of working with my customer base, the impact on the market should be very low as it's pretty rare to see customers use SE2 with RAC given the limitations of SE2.

Additional Information 

• https://www.slideshare.net/MarkusMichalewicz/oracle-rac-19c-with-standard-edition-se-2-support-update

Oracle Database 19c is Live!

I hope that by now most of you already heard the exciting news that Oracle 19c is GA on Linux x86-64 (since 25-Apr-2019) and on Oracle Solaris SPARC 64-bit (since 26-Apr-2019). Other platforms such as Windows, HP UX, IBM AIX, etc. are targeted to be release in Q2CY19 according to Document ID 742060.1 on MOS (My Oracle Support) titled "Release Schedule of Current Database Releases"

Where should I test some of the cool new features and enhancements?
You can access LiveSQL which is a cloud-based, free platform to rung and share SQL and PL/SQL. For more info, see: https://blogs.oracle.com/oracle-database/oracle-database-19c-now-available-on-livesql

How to mitigate the performance/protection trade-off in Oracle Data Guard - Part 2 (Axxana)

Introduction

In the previous blog post titled "How to mitigate the performance/protection trade-off in Oracle Data Guard"  I reviewed the common performance vs. protection trade-off between the various data protection modes in Data Guard : Maximum performance (default), maximum availability and maximum protection.

In that blog post I mentioned how far syn can be used in order to achieve both performance (due to the smaller network latency between primary and local far sync instance) while allowing for higher data protection as the far sync instance is always synced with the primary database.

The Challenge
As the far sync instance is located in a near location to the primary database (probably the same data center), what happens if the entire data center is down due to an unexpected site disaster?
In that case there is a good chance that some of the transactions are not protected as there is an asynchronous replication between the far sync instance and the standby instance. In other words, even when using Far sync, it's not possible to guarantee RPO-0 (zero data loss).

Optional Solution
One solution that I came across in several Oracle conferences (such as Oracle OpenWorld and IOUG Collaborate) which you may consider is Axxana
Axxana is like an Oracle Database "black box" which provides a protected storage unit with DR capabilities Installed at the production site, the Black Box is designed to withstand a wide variety of extreme conditions that may occur during a disaster.

According to the official Azxxana website: "Axxana’s Phoenix for Oracle Far Sync, supported by Oracle, is a self-contained, physically indestructible solution that houses, protects, and supports the Oracle Far Sync instance from within the primary (production) data center. Because a nearby data center is not needed, the risk of a nearby synchronous site failing (e.g., due to a power outage or downed communication lines) no longer exists. Zero data loss is guaranteed, increasing the probability of successful failover. In addition, because the instance can reside at the primary site, communication lines are a matter of feet instead of miles and network latency is negligible. Given that it easily and cost-effectively resolves the challenges associated with standalone versions of Far Sync, there is simply no good reason to use the Far Sync software on any other platform—or for that matter, to use three data centers. IT leaders owe it to their company and their customers to take advantage of the risk reduction, cost savings, and other opportunities that Phoenix for Oracle Far Sync offers."

How to mitigate the performance/protection trade-off in Oracle Data Guard

Introduction
The most know trade-off in Oracle Data Guard is the performance vs. protection.
Oracle Data Guard brings several protection modes, which brings companies the flexibility in choosing the right configuration in order to meet the application SLA policies.

Data Protection Modes
There are 3 protection modes in Oracle Data Guard, which can be summarized in the following table:

Data Protection Modes - Key Considerations

•  Maximum Performance = compromise on protection 
•  Maximum Protection = compromise on performance (usually)
•  Better to use at least 2 standby databases when running maximum protection
•  NET_TIMEOUT parameter of LOG_ARCHIVE_DEST_n=30 seconds (default)

Mitigating the performance/protection trade-off in Oracle Data Guard
Oracle 12cR1 introduced a feature which can enable both performance and protection for far standby environments. For example, when the standby database is very far from the primary database, setting a "maximum protection" configuration will likely affect the performance due to the network lag and it may take time to acknowledge commit back to the primary database.
In order to address this challenge, Oracle introduced a feature  called "Far Sync". Far Sync enables having a lightweight instance which resides close to the primary database and is synchronized with the primary database. This light-wight instance has only control files, standby redo logs and archived redo logs. It does not have data files and therefore it cannot be opened for access. The redo entries will be transported from the near "far sync" instance to the "regular" standby database asynchronously.
This feature enables achieving both performance (due to the smaller network latency between primary and far sync instance) while allowing for higher data protection as the far sync instance is always synced with the primary database.

Here is an illustration of this new feature:

Licensing

This feature requires having the Active Data Guard license which is an extra option in Oracle Enterprise Edition. For more information about licensing: https://docs.oracle.com/en/database/oracle/oracle-database/18/dblic/Licensing-Information.html#GUID-B6113390-9586-46D7-9008-DCC9EDA45AB4

Useful Links

• Oracle Documentation: https://docs.oracle.com/database/121/SBYDB/create_fs.htm#SBYDB5416
• White Paper: https://www.oracle.com/technetwork/database/availability/farsync-2267608.pdf

RMOUG 2019 - Slide Decks Are Available!

Hi everybody,

I'd like to share with you the slide decks I presented on April 21 in the Rocky Mountain Oracle User Group (RMOUG) conference.
Thanks to everybody who attended my sessions.

Winning Performance Challenges in Oracle Standard Editions

Oracle Diagnostics and Tuning packs offer comprehensive, valuable performance diagnostics and tuning features such as AWR, ADDM, ASH, ASH Analytics, etc. These optional packs can be licensed only on top of the Oracle Enterprise Edition. Without these packs, diagnosing performance issues may become an overly complex task even for advanced DBAs. In this session, we’ll explore how you could use Oracle’s Statspack report and dictionary views to diagnose performance issues even without using any expensive editions and packs. Also, we’ll see how Quest tools can help DBAs diagnose and solve even the most complex performance issues without relying on the Diagnostics and Tuning packs and for all the Oracle Database editions.

https://www.slideshare.net/PiniDibask/winning-performance-challenges-in-oracle-standard-editions-132800192

Oracle Data Guard for Beginners

Oracle Data Guard is one of the most important options in the Oracle Database, as it allows organizations to ensure high availability, data protection and disaster recovery for their Oracle database environments. In this session, we’ll review the Oracle Data Guard solution from A to Z.

https://www.slideshare.net/PiniDibask/oracle-data-guard-for-beginners-134714942

Oracle Multitenant Enhancements in 18c - The Good and The Bad

Introduction
Oracle Multitenant Option is the one of the most exciting enhancements in the Oracle Database probably in the last decade. It's definitely my favorite feature since 12c due to the elegant way it simplifies database consolidation projects. For more information about Oracle Multitenant, check out my blog post: http://oracledbpro.blogspot.com/2016/10/otn-appreciation-day-oracle-multitenant.html


Oracle Multitenant 18c New Features - The Good
There are several nice Oracle Multitenant related enhancements in 18c which I believe worth mentioning in this blog post

• Refreshable PDB Switchover - In Oracle 12c Release 2, Oracle introduced the refreshable PDB feature which allows to refresh a cloned PDB either on-demand or on a scheduled frequency. You can think of it as a poor-man standby because it's not designed for failover but more for having a cloned environment updated without having to completely clone the entire database every time (which may take a while). This could be very helpful for reporting/query offloading. Oracle 18c took this feature one step ahead and now enables to perform a switchover between the 2 PDBs which could be useful for load balancing purposes (planned switchover) as well as high availability when a PDB fails. Please note that this feature is not a replacement for data guard and should not be used as a DR solution for mission critical applications
• Enhanced Data Guard Integration - In Oracle 12c, when Multitenant was configured in a data guard environment there were some challenges. Oracle 12cR2 introduced the hot clone feature which was a huge improvement as it allowed cloning a PDB with no downtime; however, when hot cloning a PDB, it was not performed on standby - in other words, it wasn't replicated also in the standby CDB (similar to specifying standbys=none). In Oracle 18c this challenge has been addressed by additional steps which required to be done. For more details, see: https://www.oracle.com/technetwork/database/multitenant/learn-more/multitenantwp18c-4396158.pdf
• Snapshot Carousel - Stores historical point in time copies of pluggable databases (up to 8 in the current 18c release). This is useful for historical debugging of data related issues as well as for point-in-time recovery of a PDB (similar to flashback database feature, but without enabling flashback database)
• CDB Fleet Management - CDB allows to manage many PDBs as one (up to 4096 PDBs in Oracle Exadata and Oracle cloud, and 252 for every other deployment) - which is the main benefit of database consolidation. Now, in Oracle 18c using this new feature it's possible to manage many CDBs as one. I personally think this could be useful for the very large enterprise companies who manage huge amount of databases)

Oracle Multitenant 18c New Features - The Bad
According to Oracle documentation, all the above features (except the enhanced data guard integration), are only available either on Oracle Exadata or Oracle cloud. Most of the Oracle customers probably don't use neither Oracle Exadata nor Oracle cloud which makes these features unavailable for most Oracle customers. I hope this will be changed in the future.

Useful Links

• Oracle 18c Multitenant White Paper
• Oracle 18c Licensing Information

Winning Performance Challenges in Oracle Standard Editions

Last week (on October 4th) I presented a webinar for IOUG titled "Winning Performance Challenges in Oracle Standard Editions". For those who missed the webinar a recording is available here: http://www.ioug.org/p/cm/ld/fid=153

Abstract:
Oracle Diagnostics and Tuning packs offer comprehensive valuable performance diagnostics and tuning features such as: AWR, ADDM, ASH, ASH Analytics, etc. These optional packs can be licensed only on top of the Oracle Enterprise Edition. Without these packs, diagnosing performance issues may become a very complex task – even for advanced DBAs. In this session we will explore how you could leverage Oracle’s Statspack report and dictionary views to diagnose performance issues even without using any expensive editions and packs.  In addition we will see how Quest tools can help DBAs to diagnose and solve even the most complex performance issues without relying on the Diagnostics and Tuning packs and for all the Oracle Database editions.

Slide Deck:
Slide deck is also available (https://www.slideshare.net/PiniDibask/winning-performance-challenges-in-oracle-standard-editions)

I'd like to thank everyone who attended and if you have any follow-up questions feel free to contact me (Pini.Dibask@Quest.com).

IOUG Collaborate 2018 - Slide Decks are Available!

Last week I presented 3 sessions at my favorite Oracle conference - the IOUG Collaborate.
The slide decks for my presentations are now available:


Data Guard for Beginners
ASM Conepts, Architecture and Best Practices
Get the Oracle Performance Diagnostics Capabilities You Need without Spending a Fortune


I'd like to thank everybody who attended my sessions! Hope to see you again next year.

RMOUG 18 Slide Decks - Now Available

Hi everybody,

This week I attended the RMOUG (Rocky Mountain Oracle User Group) conference in Denver, Colorado. It was my first time attending RMOUG and I must say that although it's not a very big event (I think around 350 attendees), I was very impressed by the quality of the event and the great content which was presented by very good speakers. I highly recommend it to anybody who considers attending next year's RMOUG. It's a great place to network, learn, and have fun.

I presented 2 sessions. The slide decks are now available:

• Oracle Database Locking Mechanism Demystified
• Winning Performance Challenges in Oracle Multitenant

I'd like to thank everybody who attended my sessions! Hope to see you again next year.

ILOUG Tech Days 2018 Summary

Last week, ILOUG (Israel Oracle User Group) hosted an awesome Oracle conference in Israel which included 30 Oracle speakers from 9 countries and 45 different sessions.
This event was organized by Ami Aharonovich, Zohar Elkayam, and Oren Nakdimon, all good friends and Oracle ACEs.
It was a very well organized event, and awesome content which was delivered by 19(!) Oracle ACEs. In addition, there was a presence of Oracle Product Management as both Maria Colgan and Gerald Venzl attended and delivered several great sessions including an Oscar-candidate show of the IT Wars (DBA vs. Developer).
Also worth mentioning, Chris Saxon from Oracle presented an awesome SQL magic show :)

My session was about overcoming performance challenges when consolidating (pluggable) databases into a single Multitenant container. You can download my presentation here: https://www.slideshare.net/PiniDibask/winning-performance-challenges-in-oracle-multitenant

Thank you everyone who joined my session, and hope to see you again next year!

My Upcoming Speaker Events in H1 2018

Hi everybody,

I'd like to share with you the plans for my upcoming speaking activities for the first half of 2018:

• Israel Oracle User (ILOUG) Group Tech Days 2018 (Jan 22-23) - Very excited to present a session in one of the best Oracle conferences that ever took place in my country. I will be presenting a session titled "Winning Performance Challenging in Oracle Multitenant" on January 23rd about how to effectively monitor and diagnose performance issues in Oracle Multitenant environments and if needed implement resource management plans to ensure high QoS (Quality of Service) for the pluggable databases.
• Rocky Mountain Oracle User Group (RMOUG) Training Days (Feb 20-22) - This will be my first time attending (and speaking) at this event. I will deliver 2 sessions:
• "Winning Performance Challenging in Oracle Multitenant"- similar to the one I will be presenting at ILOUG
• "Oracle Database Locking Mechanism Demystified" - In this session I will be talking about the concepts of Oracle Database locking mechanism, advanced locking scenarios, best practices to avoid performance issues which relate to blocked SQLs, and ways to investigate lock issues using Oracle dictionary views and performance monitoring tools
• Independent Oracle User Group (April 22-26) - IOUG Collaborate is definitely my favorite Oracle Conference in the world - it's a combination of great location and very technical presentations. I got accepted to present the following sessions:
• ASM Concepts, Architecture and Best Practices - Since it was introduced back in 2003 with Oracle 10g, ASM became an essential part of almost every Oracle DBA's life. In this session you will learn ASM from A to Z - starting with the basic concepts of the ASM all the way to the new features of ASM and important best practices that will help you increase the performance and stability of your Database environments.
• Oracle Data Guard for Beginners - Oracle Data Guard is one of the most important options in the Oracle Database as it allows organizations to ensure high availability, data protection, and disaster recovery for their Oracle database environments. In this session we'll review Oracle Data Guard solution from A to Z.

I invite you all to my sessions and looking forward to meeting you there!

I'm an Oracle ACE - thank you Oracle for this recognition!

Hi everybody,

Yesterday I received the following email from the Oracle ACE Program:

"I am pleased to inform you that you have been accepted to receive the Oracle ACE award. You have been chosen based on your significant contribution and activity in the Oracle technical community. Like your fellow Oracle ACEs, you have demonstrated a proficiency in Oracle technology as well as a willingness to share your knowledge and experiences with the community."

I received this recognition from Oracle and I'm proud to be part of the awesome Oracle ACE family - thank you Oracle ACE Program!


Thank you IOUG (Independent Oracle User Group) for choosing me to present sessions at IOUG Collaborate 16 & 17 and also for inviting me to present on behalf of the IOUG at Oracle OpenWorld 2016 & 2017. I would also like to thank additional local user groups: DOAG, AOUG, OUNG for choosing me to speak at their annual user group conferences.

Here is a link to my Oracle ACE page: https://apex.oracle.com/pls/apex/f?p=19297:4:::NO:4:P4_ID:16480

ODC Appreciation Day : Online Move Data File Operation

I've decided to dedicate my ODC Appreciation Day blog post to "Online Move Data File Operation" - a feature which has been introduced in Oracle 12c.
As a quick background to this blog post, ODC (Oracle Developer Community) appreciation day is Tim Hall's (Oracle-Base) initiative which started last year (when it was OTN Appreciation Day).

So what is online move data file operation?

Moving data files is a common-use case, for example, when the DBA would like to move data files to a faster/larger disk. Another common use case is when DBA would like to migrate the files from traditional file systems to Oracle's Automatic Storage Management (more information about Oracle ASM is available in my ODC published article : https://community.oracle.com/docs/DOC-995178)

Prior to Oracle 12c, there was no way to accomplish this task with zero downtime. Common solution was to take the entire tablespace or data file offline, move it to the new location, change the location using the "ALTER DATABASE" command (which  essentially changes the location in the Oracle's control file) and then bring the tablespace/file online again; however, during this operation the entire tablespace or datafile won't be accessible. Better approach to mitigate the downtime was to change the tablespace or data file to be in a read-only mode which will at least allow queries to be executed against the data which reside on that tablespace/file - but it's still not favorable because DMLs/DDLs cannot be executed during that operation.

Oracle 12c allows us to do this completely online with zero downtime - while the database is open and users are accessing the data file. I've presented this feature with several syntax examples as part of my IOUG Collaborate 16 presentation - "Best New Features of  Oracle Database 12c" (slide deck is available here: https://www.slideshare.net/PiniDibask/best-new-features-of-oracle-database-12c).

You could also find several examples and even a short video which demonstrates this cool feature in the Oracle documentation: https://docs.oracle.com/database/121/ADMIN/dfiles.htm#ADMIN13837

Summary

Whether running Oracle databases on premise or in the cloud, this feature is very useful. When Larry Ellison spoke at Oracle OpenWorld 2017 keynotes about Oracle 18c and Oracle's option of to ensure having up to 30 minutes down-time a year with their cloud offering, this feature is another useful way  that can help when it comes to ensuring zero impact on the customer's applications (among the many other Oracle's HA & DR features - such as ASM, RAC Rolling Upgrades, Active Data Guard, Flashback, etc.)

My Oracle OpenWorld 2017 Presentation - Slide Deck is Now Available!

Last week, on October 1st, I've presented a session at Oracle OpenWorld about Database consolidation using Oracle Multitenant option.
I was invited to speak on behalf of the IOUG (Independent Oracle User Group) at Oracle OpenWorld for the second year in a row! Thank you IOUG for this great opportunity! It was fun (as always).

I got several requests to share my presentation - so here you go: https://www.slideshare.net/PiniDibask/oow-17-database-consolidation-using-the-oracle-multitenant-architecture

Oracle OpenWorld 2017 was a great experience, with some exciting announcements about the future Oracle 18c release (I will write a separate blog post about this upcoming release).

I'd also like to thank everybody who attended my session, and hope to see you again next year!

Common misconception about how Oracle handles deadlocks

Introduction

In today's blog post, I'd like to uncover a common misconception about how Oracle handles deadlocks, but first let's talk about what deadlock is. Deadlock is a locking scenario that occurs when two or more sessions are blocked as they wait because of a lock that is being held by the other session. Oracle Database automatically detects this scenario and handles this because otherwise, they will wait forever as both of them are blocked and waiting to each other’s locked resources. But the question is how does Oracle handle this? some would say that Oracle handles these scenarios by terminating one of the sessions which is known to be as the "deadlock victim" - well, that's wrong. Others would say that by rolling-back the entire transaction of one of the sessions - well, that's also wrong. So how Oracle really handles deadlock scenarios?

Deadlock Illustration

Let's see a quick example of how deadlock occurs

Step 1

Session #1 performs an update of a row (employee #151) and acquires a lock on that row

SQL> UPDATE employee
          SET first_name = 'David'
          WHERE employee_id = 151;

1 row updated.

Step 2

Session #2 performs an update of a row (employee #39) and acquires a lock on that row

SQL> UPDATE employee
          SET first_name = 'Greg'
          WHERE employee_id = 39;

1 row updated. 

Step 3

Session #1 performs an update of a row (employee #39) and is now waiting since a lock has been acquired on the same row which has not been released yet as session #2 transaction is still active

UPDATE employee
          SET first_name = 'Mark'
          WHERE employee_id = 39;

Step 4

Session #2 performs an update of a row (employee #151) and is now waiting since a lock has been acquired on the same row which has not been released yet as session #1 transaction is still active.  

SQL> UPDATE employee
          SET first_name = 'John'
          WHERE employee_id = 151;

At this stage both sessions (session #1 and session #2) are blocked  and waiting to each other’s locked resources - that's exactly what deadlock is.

So how Oracle handles deadlock scenarios?

The way Oracle handles deadlock scenarios is not by terminating one of the sessions or performing a transaction-level rollback, it's actually just by performing a statement-level rollback to one of the sessions.  The session that its statement is being rolled back, will encounter an “ORA-00060: Deadlock detected while waiting for resource.” error message (that will also be recorded in the alert log file).

Summary of Austrian Oracle User Group (AOUG) 2017 conference

Last week (on June 20th) I presented a session about the Oracle Database Locking Mechanism at the Austrian Oracle User Group (AOUG) conference.
This event took place in beautiful Vienna and was my first attending this event.
It's a small, one-day event . There were 180 attendees - small, but still very fun well-organized.
I particularly enjoyed the keynote of Maria Colgan & Gerald Venzl (both Product Managers for Oracle) about Oracle Database 12c and DevOps - it was a very amusing show in which Maria played the role of the DBA and Gerald played the role of the developer and together they showed how they can work together happily by leveraging Oracle Database 12c features and technologies.
Another session that I particularly enjoyed was presented by Maris Elsins about Mining the AWR and how to find alternative Methods for Identification of the Top SQLs in order to address various performance issues.

You can find in event page links to my presentation as well as other presentations from this event.
I'd like to thank everyone who attended my session, and I hope to see you again next year.