Glossary

This glossary defines terms used in the documentation.

API

Application Programming Interface. GemFire provides APIs to cached data for C++ and .NET applications.

application program

A program designed to perform a specific function directly for the user or, in some cases, for another application program. GemFire applications use the GemFire application programming interfaces (APIs) to modify cached data.

cache

A cache created by an application or cache server process. For the process, its cache is the point of access to all caching features and the only view of the cache that is available. Cache creation requires membership in the distributed system. See also local cache and remote cache.

cache configuration file

An XML file that declares the initial configuration of a cache, commonly named cache.xml. C++ and .NET applications can configure the cache additionally through the GemFire programming APIs.

cache listener

User-implemented plug-in for receiving and handling region entry events. A region’s cache listener is called after an entry in the local cache is modified.

cache loader

User-implemented plug-in for loading data into a region. A region’s cache loader is used to load data that is requested of the region but is not available in the distributed system. For a distributed region, the loader that is used can be in a different cache from the one where the data-request operation originated. See also cache writer and netSearch.

cache server

A long-running, configurable caching process, generally used to serve cached data to the applications. Usually, cache servers are configured to operate as servers in a client-server typology and their regions are configured to be replicates. See also server.

cache writer

User-implemented plug-in intended for synchronizing the cache with an outside data source. A region’s cache writer is a synchronous listener to cache data events. The cache writer has the ability to abort a data modification. See also cache loader.

caching enabled

Specifies whether data is cached in the region. GemFire gives you the option of running applications without entry caching. For example, you can configure a distributed system as a simple messaging service.

client

In a client-server topology, clients can connect to cache servers, create new regions on the cache server, and store data in the cache server region. Clients can also connect to existing regions on a cache server and do directed gets and puts on the cache server. Clients do not track membership information about other clients, nor do they share information with other clients.

concurrency level

An estimate of the number of threads expected to concurrently modify values in the region. The actual concurrency may vary; this value is used to optimize the allocation of system resources.

connection

What an application uses to access a GemFire distributed system. An application can connect to a GemFire system by calling the DistributedSystem::connect function with the appropriate parameter settings. An application must connect to a distributed system to gain access to GemFire functionality.

destroy

Remove an entry from a region or remove a region from a cache.

disk policy

Determines whether LRU entries exceeding the entries limit for a caching region are destroyed or written to disk.

distributed scope

Enables a region to automatically send entry value updates to remote caches and incorporate updates received from remote caches. The scope identifies whether distribution operations must wait for acknowledgement from other caches before continuing. A distributed region’s cache loader and cache writer (defined in the local cache) can be invoked for operations originating in remote caches.

distributed system

One or more GemFire system members that have been configured to communicate with each other, forming a single, logical system. Also used for the object that is instantiated to create the connection between the distributed system members.

DTD

Document Type Definition. A language that describes the contents of a Standard Generalized Markup Language (SGML) document. The DTD is also used with XML. The DTD definitions can be embedded within an XML document or in a separate file.

entry

A data object in a region. A region entry consists of a key and a value. The value is either null (invalid) or an object. A region entry knows what region it is in. See also region data, entry key, and entry value.

entry key

The unique identifier for an entry in a region.

entry value

The data contained in an entry.

expiration

A cached object expires when its time-to-live or idle timeout counters are exhausted. A region has one set of expiration attributes for itself and one set for all region entries.

expiration action

The action to be taken when a cached object expires. The expiration action specifies whether the object is to be invalidated or destroyed, and whether the action is to be performed only in the local cache or throughout the distributed system. A destroyed object is completely removed from the cache. A region is invalidated by invalidating all entries contained in the region. An entry is invalidated by having its value marked as invalid.

Expiration attributes are set at the region level for the region and at the entry level for entries. See also idle timeout and time-to-live.

factory method

An interface for creating an object which at creation time can let its subclasses decide which class to instantiate. The factory method helps instantiate the appropriate subclass by creating the correct object from a group of related classes.

idle timeout

The amount of time a region or region entry may remain in the cache unaccessed before being expired. Access to an entry includes any get operation and any operation that resets the entry’s time-to-live counter. Region access includes any operation that resets an entry idle timeout, and any operation that resets the region’s time-to-live.

Idle timeout attributes are set at the region level for the region and at the entry level for entries. See also time-to-live and expiration action.

interest list

A mechanism that allows a region to maintain information about receivers for a particular key-value pair in the region, and send out updates only to those nodes. Interest lists are particularly useful when you expect a large number of updates on a key as part of the entry life cycle.

invalid

The state of an object when the cache holding it does not have the current value of the object.

invalidate

Remove only the value of an entry in a cache, not the entry itself.

listener

An event handler. The listener registers its interest in one or more events and is notified when the events occur.

load factor

A region attribute that sets initial parameters on the underlying hashmap used for storing region entries.

local cache

The part of the distributed cache that is resident in the current process. This term is used to differentiate the cache where a specific operation is being performed from other caches in the distributed system. See also remote cache.

local scope

Enables a region to hold a private data set that is not visible to other caches. See also scope.

LRU

Least Recently Used. Refers to a region entry or entries most eligible for eviction due to lack of interest by client applications.

LRU entries limit

A region attribute that sets the maximum number of entries to hold in a caching region. When the capacity of the caching region is exceeded, LRU is used to evict entries.

membership

Applications and cache servers connect to a GemFire distributed system by invoking the static function DistributedSystem::connect. Through this connection, the application gains access to the APIs for distributed data caches. When a C++ or .NET application connects to a distributed system, it specifies the system it is connecting to by indicating the communication protocol and address to use to find other system members.

netSearch

The method used by GemFire to search remote caches for a data entry that is not found in the local cache region. This operates only on distributed regions.

overflows

An eviction option that causes the values of LRU entries to be moved to disk when the region reaches capacity. See disk policy.

persistence manager

The persistence manager manages the memory-to-disk and disk-to-memory actions for LRU entries. See overflows.

region

A logical grouping of data within a cache. Regions are used to store data entries (see entry). Each region has a set of attributes governing activities such as expiration, distribution, data loading, events, and eviction control.

region attributes

The class of attributes governing the creation, location, distribution, and management of a region and its entries.

region data

All of the entries directly contained in the region.

region entry

See entry.

remote cache

Any part of the distributed cache that is resident in a process other than the current one. If an application or cache server does not have a data entry in the region in its local cache, it can do a netSearch in an attempt to retrieve the entry from the region in a remote cache. See also local cache.

scope

Region attribute. Identifies whether a region keeps its entries private or automatically sends entry value updates to remote caches and incorporates updates received from remote caches. The scope also identifies whether distribution operations must wait for acknowledgement from other caches before continuing. See also distributed scope and local scope.

serialization

The process of converting an object graph to a stream of bytes.

server

In a client-server topology, the server manages membership and allows remote operations. The server maintains membership information for its clients in the distributed system, along with information about peer applications and other servers in the system. See also cache server.

system member

A process that has established a connection to a distributed system.

time-to-live

The amount of time a region or region entry may remain in the cache without being modified before being expired. Entry modification includes creation, update, and removal. Region modification includes creation, update, or removal of the region or any of its entries.

Time-to-live attributes are set at the region level for the region, and at the entry level for entries. See also idle timeout and expiration action.

XML

EXtensible Markup Language. An open standard for describing data from the W3C, XML is a markup language similar to HTML. Both are designed to describe and transform data, but where HTML uses predefined tags, XML allows tags to be defined inside the XML document itself. Using XML, virtually any data item can be identified. The XML programmer creates and implements data-appropriate tags whose syntax is defined in an XSD (XML schema definition) or a DTD (Document Type Definition) file.

XML schema definition

The definition of the structure, content, and semantics used in an XML document. The definition can be used to verify that each item of content in a document adheres to the specification of the element in which the content is placed. The XML schema is a superset of DTD. Unlike DTD, XML schemas are written in XML syntax, which, although more verbose than DTD, are more descriptive and can have stronger typing. Files containing XML schema definitions generally have the XSD extension.

XSD

See XML schema definition.