Commit Scopes

Fully managable and configurable commit scopes are a feature of PGD Expanded.

PGD Expanded offers a range of synchronous modes to complement its default asynchronous replication. You use commit scopes to configure these synchronous modes. Commit scopes are rules that define how PGD handles synchronous operations and when the system considers a transaction committed.

PGD Essential offers a limited set of commit scopes that are pre-defined and cannot be changed.

Introducing

• :ref:`Overview of durability options <Overview of durability options>`  introduces the concepts and some of the essential terminology that's used when discussing synchronous commits.
  

• :ref:`Durability terminology <Durability terminology>`  lists terms used around PGD's durability options, including how to refer to nodes in replication.
  

• :ref:`Commit scopes <Commit scopes>`  is a more in-depth look at the structure of commit scopes and how to define them for your needs.
  

• :ref:`Predefined commit scopes <Predefined commit scopes>`  lists the pre-defined commit scopes that are available in PGD Essential.
  

• :ref:`Commit scope groups <Commit scope groups>`  introduces the notion of an origin group, and how to leverage these when defining commit scopes rules.
  

• :ref:`Commit scope rules <Commit scope rules>`  looks at the syntax of and how to formulate a commit scope rule.
  

• :ref:`Comparing durability options <Comparing durability options>`  compares how commit scope options behave with regard to durability.
  

• :ref:`Degrading commit scope rules <Degrading commit scope rules>`  shows how to set up a commit scope rule that can gracefully degrade to a lower setting in case of timeouts with a stricter setting.
  

Commit scope kinds

• :ref:`SYNCHRONOUS COMMIT <SYNCHRONOUS COMMIT>`  is a commit scope mechanism that works in a similar fashion to legacy synchronous replication, but from within the commit scope framework.
  

• :ref:`QUORUM COMMIT <QUORUM COMMIT>`  is the commit scope kind for workloads requiring distributed transaction consistency. Quorum Commit guarantees that all participating nodes commit together or roll back together, preventing conflicts before they occur.
  

• :ref:`Commit At Most Once <Commit At Most Once>`  focuses on the Commit At Most Once option, in which applications take responsibility for verifying that a transaction has been committed before retrying. This ensures that their commits only happen at most once.
  

• :ref:`LAG CONTROL <LAG CONTROL>`  looks at the commit scope mechanism which dynamically throttle nodes according to the slowest node and regulates how far out of sync nodes may go when a database node goes out of service.
  

• :ref:`Group Commit (legacy) <Group Commit (legacy)>`  focuses on the Group Commit option, where you can define a transaction as done when a group of nodes agrees it's done.
  

Working with commit scopes

• :ref:`Administering <Administering>`  addresses how to manage a PGD cluster with commit scopes in use.
  

• :ref:`Legacy synchronous replication using PGD <Legacy synchronous replication using PGD>`  shows how you can still access traditional Postgres synchronous operations under PGD.
  

• :ref:`Internal timing of operations <Internal timing of operations>`  compares legacy replication with PGD's async and synchronous operations, especially the difference in the order by which transactions are flushed to disk or made visible.
  

• Overview of durability options
  • Overview
• Durability terminology
  • Durability terminology
    • Nodes
• Commit scopes
  • Commit scope structure
  • How a commit scope is selected
  • Creating a Commit Scope
  • Using a commit scope
• Predefined commit scopes
  • local protect
  • lag protect
  • majority protect
  • adaptive protect
  • Examples
• Commit scope groups
  • Quantifiers
  • Group specifiers
    • Explicit group name
    • CLUSTER
    • ORIGIN_GROUP
    • NOT ORIGIN_GROUP
    • FOR EACH GROUP
    • FOR EACH GROUP IN CLUSTER
  • Combining groups
    • Requiring a local majority plus a remote confirmation
    • Requiring all local nodes plus a remote confirmation
• Commit scope rules
  • The commit scope group
  • The confirmation level
  • The commit scope kinds
    • SYNCHRONOUS COMMIT
    • QUORUM COMMIT
    • CAMO
    • LAG CONTROL
• Comparing durability options
  • Comparison
    • ON RECEIVED
    • ON REPLICATED
    • ON DURABLE
    • ON VISIBLE
• Degrading commit scope rules
  • Behavior
  • SYNCHRONOUS COMMIT and GROUP COMMIT
  • CAMO
  • Monitoring degrade events
    • Example monitoring query
• Synchronous Commit
  • Overview
  • Example
  • Configuration
  • Confirmation
  • Details
• Quorum Commit
  • Overview
  • When to use Quorum Commit
    • How Quorum Commit works
    • Using Quorum Commit
• Commit At Most Once
  • Overview
  • Configuration
  • Confirmation
  • Limitations
  • Failure scenarios
    • Data persistence at receiver side
    • Asynchronous mode
    • Example
    • With asynchronous mode
    • Without asynchronous mode
  • Application use
    • Overview and requirements
    • Working with the CAMO partner
    • Connection pools and proxies
  • CAMO limitations
  • Performance implications
  • Client application testing
• Lag Control
  • Overview
  • Background
  • Requirements
  • Configuration
  • Confirmation
  • Transaction application
  • Limitations
  • Caveats
  • Meeting organizational objectives
  • Lag Control and extensions
• Group Commit (legacy)
  • Overview
  • Example
  • Requirements
  • Limitations
  • Configuration
  • Confirmation
  • Behavior
    • Commit decisions
    • Conflict resolution
    • Aborts
    • Transaction reconciliation
  • Eager conflict resolution
    • Usage
    • Error handling
    • Effects of Eager Replication in general
    • Increased abort rate
    • Effects of MAJORITY and ALL node replication in general
    • Increased commit latency
• Administering
  • Planned shutdown and restarts
• Legacy synchronous replication using PGD
  • Usage
  • Comparison
  • Postgres configuration parameters
  • Migration to commit scopes
• Internal timing of operations