Ioan Rogers > Prophet > doc/glossary

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FALLACIES OF DISTRIBUTED COMPUTING ^

The Fallacies of Distributed Computing are a set of common but flawed assumptions made by programmers when first developing distributed applications. The fallacies are summarized as follows:

  1. The network is reliable.
  2. Latency is zero.
  3. Bandwidth is infinite.
  4. The network is secure.
  5. Topology doesn't change.
  6. There is one administrator.
  7. Transport cost is zero.
  8. The network is homogeneous.

GLOSSARY ^

Database

A term to describe a uniquely identified set of object types and records sharing a single 'base' revision and Replica identifier

A database contains multiple Records

Has one: uuid

Replica

An instance of a database. Replicas are expected to contain all Changesets from any other replica they have been synchronized with, but those Changesets are not guaranteed to be in the same sequence on each replica

Has one: uuid

Changeset

A changeset contains "old" and "new" versions of a set of database "Records", they can be of any Record Type.

Has one: source_uuid, sequence_no

Has many: changes

Change

An entry in a changeset. Contains all the updates to a given record for this changeset

Record

A Record is composed of zero or more Attributes and a universally unique identifier. Each record is categorized into a Record Type.

Has one: uuid

Has many: attributes

Record Type

A Record Type is a category or "bucket" for zero or more records applications may define specific behaviours for Records of a certain Record Type, but Prophet does no more than to tag Records with a Record Type. Record Types are uniquely identified with a textual name and a UUID

Has one: textual label, uuid

Attribute

A key-value pair on a Record.

Has one: key, value

Conflict

A Conflict occurs when a Changeset is being applied and the current state of a Replica meets any of the following criteria:

Resolution

When the local Replica

Export/Publish

Exporting is the act of cloning a replica. The replica uuid (which is its identity) remains the same. An exported replica is useful for copying to another machine or USB stick, so that other people may pull your changes.

Publishing a replica just export it to another machine, usually over ssh.

Exporting or publishing to an existing replica just updates that replica, it does not perform a merge, since the replica uuid is the same for both copies.

Push/Pull

Pushing and pulling merge changes from two different replicas. Pushing to or pulling from an empty replica creates it and assigns it a new replica uuid.

Foreign Replica

A (possibly read-only) data store that is not a Prophet replica (such as RT or Twitter). A Prophet replica can act as a gateway to a foreign replica.

NON-TERMS ^

Node

Too many things get called records

revision

Revision is a term from version control. the backing store may describe it but it's not a Prophet term

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