The Wolfram Language allows values to be set up to be persistent beyond a single invocation of the language. The persistent values can be stored in a variety of locations, locally or in the cloud. Values can either be retrieved from a single location or can be aggregated from multiple locations. Persistent values are used, for example, to support web sessions, and also for general system initialization.

Referencing Persistent Values

PersistentSymbol — settable persistent value

PersistentObject — an object representing a stored persistent value

Persistence Locations

PersistenceLocation — symbolic specification of a persistence location

"KernelSession" — current invocation of the Wolfram Language kernel

"FrontEndSession" — current invocation of the Wolfram notebook front end

"Notebook" — stored in the current notebook

"Local" — local to a computer, based on user home directory

"LocalShared" — local to a computer, based on $BaseDirectory

"Cloud" — in the cloud defined by the current $CloudBase

"Installation" — built-in default settings for a given installation

$PersistenceBase — default location at which to store newly defined persistent values

$PersistencePath — default locations at which to look for requested persistent values

Managing Persistent Values

MergingFunction — option to define how to merge values from different locations

PersistentObjects — persistent objects with names matching a pattern

Persistent Values Used for Initialization »

InitializationValue — persistent settable value initialized when sessions are started

InitializationObjects — give existing initialization objects

$Initialization — symbol whose value is released and evaluated at startup

$InitializationContexts  ▪  $PreInitialization  ▪  Initialize  ▪  ...