Durability
==========

EDB Postgres Distributed (PGD) offers a range of synchronous modes to
complement its default asynchronous replication. These synchronous modes
are configured through commit scopes: rules that define how operations
are handled and when the system should consider a transaction committed.

Introducing
-----------

-  :ref:`Monitoring overview <Monitoring overview>`  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 nodes are referred to 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:`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 each option behaves.

Commit scope kinds
------------------

-  :ref:`Group commit <Group commit>`  focuses on the Group Commit option, where you can
   define a transaction as done when a group of nodes agrees it’s done.

-  :ref:`Upgrading a CAMO-enabled cluster <Upgrading a CAMO-enabled cluster>`  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:`PGD Synchronous Commit <PGD Synchronous Commit>`  examines a commit scope mechanism which works in a
   similar fashion to legacy synchronous replication, but from within
   the commit scope framework.

Working with commit scopes
--------------------------

-  :ref:`Administering PGD Proxy <Administering PGD Proxy>`  addresses how a PGD cluster with Group Commit in use
   should be managed.

-  :ref:`Limitations <Limitations>`  lists the various combinations of durability options
   which are not currently supported or not possible. Do refer to this
   before deciding on a durability strategy.

-  :ref:`Legacy synchronous replication using PGD <Legacy synchronous replication using PGD>`  shows how traditional Postgres synchronous operations
   can still be accessed under PGD.

-  :ref:`Internal timing of operations <Timing considerations and synchronous replication>`  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.

.. toctree::
  :maxdepth: 3

  PGD_Features--durability--overview
  PGD_Features--durability--durabilityterminology
  PGD_Features--durability--commit-scopes
  PGD_Features--durability--commit-scope-rules
  PGD_Features--durability--comparing
  PGD_Features--durability--Commit_Scope_kinds--index
  PGD_Features--durability--Working_with--index