Understanding Oracle RAC 12.1.0.2 Internals the Cache Fusion Edition

Understanding Oracle RAC (12.1.0.2) Internals: The Cache Fusion Edition Markus Michalewicz Director of Product Management Oracle Real Application Clusters (RAC) October 1st, 2014 @OracleRACpm http://www.linkedin.com/in/markusmichalewicz http://www.slideshare.net/MarkusMichalewicz

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The Secret to the Scalability of Any System – A straight vertical line

Simplification 1 Copyright © 2014, Oracle and/or its affiliates. All rights reserved.

Simplification 2 4

Three Alternative Architectures – The Same Idea Applies

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Three Alternative Architectures – The Same Idea Applies

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Program Agenda 1

Cache Fusion Overview

2

(Dynamic Re-) Mastering

3

Handling Contentions

4

RAC Meets Multitenant

5

RAC Meets In-Memory

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Program Agenda 1

Cache Fusion Overview

2

(Dynamic Re-) Mastering

3

Handling Contentions

4

RAC Meets Multitenant

5

RAC Meets In-Memory

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Oracle RAC Combines it All & Adds Services • Requester • Listener • Service • Holder

Block, unless otherwise stated. Instance

• Master • Session

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PQ/PX:

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Listeners and Services Direct Work to an Instance • In an Oracle environment, listeners establish connections with an instance. • In an Oracle RAC environment two types of listeners are used (for this purpose): 1. SCAN and SCAN Listener 2. Local Listeners per node

• Services are used to load balance work. • Local listeners will establish connections on instances where the service is offered. • Once a session is established within an instance, the sessions stays until closed.

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Getting Access to Data

• Local Cache Hit

• Remote Cache Hit

• Access time: nanoseconds

• Data is on disk

• Access time: microseconds

• Flash cache access time: microseconds • Disk controller cache: access time: micros.

Whether local or remote, cache hits are always faster than reading from spinning disks

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• Spinning disk access time: milliseconds

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Maximum Three Way Communication write

write

write

Message

Message

Block

Case 1 (all local)

Case 2 (local / remote)

Case 3 (all distributed)

• All entities in one instance

• Some entities in one instance

• All entities are dispersed

• Data holding instance

•Data holding instance

• Session “holding” instance

• Session “holding” instance

• Mastering Instance

• Three way communication to obtain a given block of data

• Two way communication

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• Message

operations have been subject to improvements since Oracle RAC 10g times.

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Dynamic Retrieval of Data +

1

2 3

+

• In order to fulfill a given request, Oracle RAC can decide to: • Assemble data spread across instances and disks • Perform a (full) disk read for (parts of) the data • Use assembly and (full) disk reads dynamically

• The decision which access path to use is dependent on various factors (e.g. IO capacity, network utilization) • Respective parameters are monitored • The access path can change accordingly and dynamically.

Once data has been shipped to an instance, it resides in the cache for further (local) access. Updates will be communicated as required (via messages). Copyright © 2014, Oracle and/or its affiliates. All rights reserved.

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Program Agenda 1

Cache Fusion Overview

2

(Dynamic Re-) Mastering

3

Handling Contentions

4

RAC Meets Multitenant

5

RAC Meets In-Memory

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Mastering and Dynamic Re-Mastering write

write

Oracle RAC

Oracle RAC

Oracle RAC

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• In Oracle RAC, every object is mastered (as part of Global Cache Services / GCS) by an instance. • The Global Resource Directory (GRD) is used to “keep track” of mastering. • Illustration above is symbolic for this matter.

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• If a session requests write access to a block that is not mastered by the instance hosting the session, the master instance needs to be contacted (via message).

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• Based on user access patterns, a Dynamic Re-Mastering (DRM) can be triggered, changing the master for an object from one instance to another. • Relocating the master to the instance where data is requested most reduces the messaging.

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Dynamic Re-Mastering (DRM) – Recommendations • DRM is used internally and externally.

write

• Externally means access patterns can influence the mastering of user data. • Internally

DRM is used for the management of UNDO data across instances for example.

• DRM activity is also performed upon instances leaving or joining the cluster.

• Do not turn DRM off (_gc_policy_time=0)! Oracle RAC

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• Optimize _gc_policy_minimum to run / trigger DRM at a convenient moment under normal operations.

• Consider using smaller SGA sizes. • See MOS note 1619155.1 – “Best Practices and Recommendations for RAC databases using SGA larger than 300GB” as applicable • “dbms_cacheutil” can be used to manually set and release affinity under well understood circumstances.

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New in 12.1.0.2: Cache Fusion Accelerator • The Cache Fusion Accelerator (CFA) is an

write

• OS kernel (Linux & Solaris only) module • which can respond directly to certain lock requests via RDSv3.

• The lock state is saved in memory shared by the database and the kernel.

• CFA saves user/kernel context switches, frees up CPU cycles in LMS, and “speeds up” messages. Oracle RAC

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• CFA will be activated on Engineered Systems over time, including the Oracle Database Appliance.

Lock grant

• CFA contributes to a better, linear scaling. • CFA is one of a long list of improvements.

LMS process

Accelerator

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New in 12.1.0.2: Cache Fusion Accelerator • The Cache Fusion Accelerator (CFA) is an

write

• OS kernel (Linux & Solaris only) module • which can respond directly to certain lock requests via RDSv3.

• The lock state is saved in memory shared by the database and the kernel.

• CFA saves user/kernel context switches, frees up CPU cycles in LMS, and “speeds up” messages. Oracle RAC

Oracle RAC

Oracle RAC

Oracle GI

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• CFA will be activated on Engineered Systems over time, including the Oracle Database Appliance. • CFA contributes to a better, linear scaling. • CFA is one of a long list of improvements.

LMS process

Accelerator

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Program Agenda 1

Cache Fusion Overview

2

(Dynamic Re-) Mastering

3

Handling Contentions

4

RAC Meets Multitenant

5

RAC Meets In-Memory

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How To Handle Contention – Basics write write write write

write write write write write write

write write write write

• Contention can occur in any multiuser system (even in SI databases)

• You can still guide users to only one instance in an Oracle RAC environment.

• From a contention perspective, a 2-node setup is basically the same as a 3 or more nodes setup.

• User data as well as “metadata” (e.g. an index) can be subject to contention

• As soon as you scale out, contention can occur between instances (not only within an instance).

• The difference is in the required messagebased communication to obtain a block considering the mastering.

Note: for scalability, only write/write contention needs to be considered. Copyright © 2014, Oracle and/or its affiliates. All rights reserved.

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How To Handle Contention – Considerations write write write write

write write write write

write write write write

Sequence

REDO

• Frequent transactional changes to the same data blocks in all instances may result in “write hot spots”. • Block with pending changes may be “pinged” by other instances.

• Pending redo must be written to log before the block can be transferred • Latency for a deferred block transfer becomes dependent on delay for log IO

• Contention can affect related data as much as it can affect the actual “user data”. • Right growing indexes and index contention are common. • In 99% of OLTP performance issues,

write hot spots occur on indexes.

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How To Handle Contention – General Solutions write write write write

write write write write

write write write write

Sequence

REDO

• Avoid frequent transactional changes to the same data blocks in all instances using partitioning and services. • Logically partition data so that subdata is handled in one instance only. Guide users via services accordingly.

• Place redo logs on fast storage if performance critical; e.g. SSDs

• Use either for better cache locality: • Global hash partitioned indexes • Locally partitioned indexes

•Implemented in 11.2.2.4 of Exadata and Oracle Database Appliance by default (Smart Logs and SSDs, respectively)

•Separate disks for logs from other IO busy disks

• Drop unused indexes

Get the best out of Oracle Partitioning - A practical guide and reference https://www.slideshare.net/secret/nHJV1CjWWOlGOl Copyright © 2014, Oracle and/or its affiliates. All rights reserved.

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How To Handle Contention – Use Connection Pools Connection Pool

• UCP supports “Connection Affinity”: • Transaction-Based Affinity

• Web Session Affinity http://docs.oracle.com/database/121/JJUCP/rac.htm#JJUCP8197

write write write write Connectionwrite Pool write

• Connection Pools limit the number of connections to the database – example: • Oracle Universal

Connection Pool (UCP)

• Use “Database Resident Connection Pooling” when no. of active sessions much smaller then no. of open session.

Connection Pool

busy

idle

• Fast Application Notification (FAN) – enabled connection pools receive Load Balancing information based on the Workload Repository and on a per-service basis.

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Program Agenda 1

Cache Fusion Overview

2

(Dynamic Re-) Mastering

3

Handling Contentions

4

RAC Meets Multitenant

5

RAC Meets In-Memory

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Oracle Multitenant and Oracle RAC – a Symbiosis

cons_1

cons_2

Oracle RAC Oracle GI | HUB

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REDO

•Pluggable Databases (PDBs) represent themselves as services in an Oracle RAC Multitenant Database, ensuring extremely fast failover.

• Oracle RAC Multitenant Databases help to consolidate.

• PDBs can be used to conveniently align users to instances with all the benefits, providing higher consolidation benefit and agility.

• Future improvements will ensure greater efficiency. • Multithreaded Redo Log writer already implemented.

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Oracle Multitenant and Oracle RAC – a Symbiosis

cons_1

cons_2

Oracle RAC Oracle GI | HUB

Oracle RAC Oracle GI | HUB

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REDO

•Pluggable Databases (PDBs) represent themselves as services in an Oracle Multitenant Database, ensuring extremely failover. MoreRAC information, see: Oracle Multitenant meetsfast Oracle RAC -

• Oracle RAC Multitenant Databases help to consolidate.

• PDBshttp://www.slideshare.net/MarkusMichalewicz/oraclecan be used to conveniently align users to instances with multitenant-meets-oracle-rac-ioug-2014-version all the benefits, providing higher consolidation benefit and agility.

• Future improvements will ensure greater efficiency. • Multithreaded Redo Log writer already implemented. • Per-PDB/service optimized GCS operations coming in future. Copyright © 2014, Oracle and/or its affiliates. All rights reserved.

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Program Agenda 1

Cache Fusion Overview

2

(Dynamic Re-) Mastering

3

Handling Contentions

4

RAC Meets Multitenant

5

RAC Meets In-Memory

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Oracle In-Memory and Oracle RAC Breakthrough: Dual Format Database

Generate Reports Instantly

In-Memory Column Store Column Store Replaces Analytic Indexes

Full HA & Integration with Industry Standards

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Oracle In-Memory and Oracle RAC – A Dream-Team Breakthrough: Dual Format Database

Addresses

In-Memory Column Store Column Store Replaces Analytic Indexes

Addresses

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“Full support for RAC scale-out means Oracle Database In-Memory can be used on our largest Data Warehouse, enabling more near real-time analytics.” – Sudhi Vijayakumar, Senior Oracle DBA Yahoo Inc.

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Oracle Database In-Memory: Unique Fault Tolerance • Similar to storage mirroring • Duplicate in-memory columns on another node • Enabled per table/partition • Application transparent

• Downtime eliminated by using duplicate after failure Only Available on Engineered Systems

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“Downtime is extremely costly for our business. Oracle’s In-Memory architecture takes the right approach to balancing real-time speed with continuous availability.” – Jens-Christian Pokolm Analyst IT-DB Architecture & Engineering Postbank Systems AG

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Optimized Used of Memory in Every Layer • Compressed • Lock mgmt. simplified

In-Memory Format

In-Memory Format

Normal Buffer Cache

Normal Buffer Cache

? Oracle RAC

? Oracle RAC

? Oracle RAC

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Coming soon…

• In-Memory compresses data, optimizing the use of memory. • Memory allocated for In-Memory is subject to simplified lock mgmt.

• PCI Flash works mostly locally.

• In-Memory Speed and Capacity of Low Cost Disk

• Shared solutions require RAC external synchronization. • Coming soon on ODA: a fully integrated shared flash cache.

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Oracle Learning Streams: http://education.oracle.com/streams/ • Database and Middleware streams available • Videos – Feature different groups and presenters – Cover a broad range of topics and products

• FREE OF CHARGE Oracle RAC PM / Dev contributions: – Oracle Flex Cluster: Optimized Resource Management for the Cloud - Ian Cookson – Oracle Grid Infrastructure 12c Bundled Agents – Shankar Iyer – ACFS Product Overview and Use Cases - Ara Shakian – The Oracle Real Application Clusters (RAC) Family of Solutions - A User Guide – Markus Michalewicz – Next Generation Oracle Automatic Storage Management - Jim Williams – Implementing DBaaS with Oracle RAC 12c and Quality of Service Management - Mark Scardina – Oracle RAC Practical Performance Management and Tuning – Markus Michalewicz Copyright © 2014, Oracle and/or its affiliates. All rights reserved.

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