💻IT: Latency (Definitions)

"The fixed cost of servicing a request, such as sending a message or accessing information from a disk. In parallel computing, the term most often is used to refer to the time it takes to send an empty message over the communication medium, from the time the send routine is called to the time the empty message is received by the recipient. Programs that generate large numbers of small messages are sensitive to the latency and are called latency-bound programs." (Beverly A Sanders, "Patterns for Parallel Programming", 2004)

"The amount of time it takes a system to deliver data in response to a request. For mass storage devices, it is the time it takes to place the read or write heads over the desired spot on the media. In networks, it is a function of the electrical and software properties of the network connection." (Tom Petrocelli, "Data Protection and Information Lifecycle Management", 2005)

"The time delay it takes for a network packet to travel from one destination to another." (John Goodson & Robert A Steward, "The Data Access Handbook", 2009)

"The time it takes for a system to respond to an input." (W Roy Schulte & K Chandy, "Event Processing: Designing IT Systems for Agile Companies", 2009)

"A period of time that the computer must wait while a disk drive is positioning itself to read a particular block of data." (Rod Stephens, "Start Here!™ Fundamentals of Microsoft® .NET Programming", 2011)

"The measure of time between two events, such as the initiation and completion of an event, or the read on one system and the write to another system." (DAMA International, "The DAMA Dictionary of Data Management", 2011)

"The time period from start to completion of a unit of work." (Max Domeika, "Software Development for Embedded Multi-core Systems", 2011)

"The time it takes to complete a task - that is, the time between when the task begins and when it ends. Latency has units of time. The scale can be anywhere from nanoseconds to days. Lower latency is better in general." (Michael McCool et al, "Structured Parallel Programming", 2012)

"The amount of time lag before a service executes in an environment. Some applications require less latency and need to respond in near real time, whereas other applications are less time-sensitive." (Marcia Kaufman et al, "Big Data For Dummies", 2013)

"A delay. Can apply to the sending, processing, transmission, storage, or receiving of information." (Mike Harwood, "Internet Security: How to Defend Against Attackers on the Web" 2nd Ed., 2015)

"A period of waiting for another component to deliver data needed to proceed." (Faithe Wempen, "Computing Fundamentals: Introduction to Computers", 2015)

"The time it takes for the specified sector to be in position under the read/write head" (Nell Dale & John Lewis, "Computer Science Illuminated" 6th Ed., 2015)

"The delay between when an action such as transmitting data is taken and when it has an effect." (O Sami Saydjari, "Engineering Trustworthy Systems: Get Cybersecurity Design Right the First Time", 2018)

🛢DBMS: Federated Database (Definitions)

"A database that is spread across multiple servers, often in multiple geographical locations, is called a federated database. The servers that hold the different parts of a federated database are referred to as a federation, or federated database servers. A federation of database servers is used to spread the processing load across a group of servers. The data is horizontally partitioned allowing each of the servers to be independently managed, but distributed queries can be used to process requests on the entire database." (Darril Gibson, "MCITP SQL Server 2005 Database Developer All-in-One Exam Guide", 2008)

"A database system wherein constituent databases, that are geographically decentralized and using various computer systems, are interconnected via a computer network or software that allows metasearching via a single platform. Since the constituent database systems remain autonomous, a federated database system is a contrastable alternative to the task of merging together several disparate databases." (Mila M. Ramos et al, "The CGIAR Virtual Library Bridging the Gap Between Agricultural Research and Worldwide Users", 2009)

"A set of databases that are documented and then interconnected to operate as one database, even when those databases are on different platforms." (DAMA International, "The DAMA Dictionary of Data Management", 2011)

[federated data warehouse:] "1.A conceptual Data Warehouse made up of multiple decision support databases, potentially on multiple servers, but presented transparently to Business Intelligence users as a unified schema for query, analysis, and reporting. 2.An Enterprise Data Warehouse fed by extracts from departmental Data Warehouses and/or legacy Data Warehouses prior to their incorporation and/or retirement." (DAMA International, "The DAMA Dictionary of Data Management", 2011)

"A distributed database management system (DBMS) that consists of a DB2 instance that operates as a server, a database that serves as the federated database, one or more data sources, and clients (users and applications) who access the database and data sources. A federated system can be used to query and manipulate data that is located on other data servers." (Sybase, "Open Server Server-Library/C Reference Manual", 2019)

"In a federated system, the database that is within the federated server. Users and applications interface with the federated database. To these clients, the data sources and the federated database seem to be a single database." (Sybase, "Open Server Server-Library/C Reference Manual", 2019)

"A set of linked servers that shares the processing load of data by hosting partitions of a distributed partitioned view." (Microsoft Technet)

"A system in which multiple databases appear to function as a single entity. However, the databases typically involved in this kind of system exists independently of the others. Once the different databases are 'combined', one federated database is formed." (Solutions Review)

🛢DBMS: Data Synchronization (Definitions)

"In replication, the process that ensures the publication and destination tables contain the same schema and data. This process must occur before a subscription server can receive replicated transactions from an article or a publication." (Patrick Dalton, "Microsoft SQL Server Black Book", 1997)

"Refers to the process in which the article or articles subscribed to on a subscription server are initially synchronized with the original article or articles on the publication server." (Owen Williams, "MCSE TestPrep: SQL Server 6.5 Design and Implementation", 1998)

[automatic synchronization:] "Synchronization that is accomplished automatically by SQL Server when a server initially subscribes to a publication. A snapshot of the table data and schema are written to files for transfer to the Subscriber. The table schema and data are transferred by the distribution agent. No operator intervention is required." (Microsoft Corporation, "SQL Server 7.0 System Administration Training Kit", 1999)

"The process of maintaining the same schema and data in a publication at a Publisher and in the replica of a publication at a Subscriber. See also initial snapshot." (Microsoft Corporation, "SQL Server 7.0 System Administration Training Kit", 1999)

"The process of ensuring that the publication and destination tables contain the same schema and data. This process must occur before a new Subscriber can receive replicated transactions from a publication. It is also called initial synchronization." (Microsoft Corporation, "Microsoft SQL Server 7.0 Data Warehouse Training Kit", 2000)

"Synchronization is the process in replication of maintaining the same schema and data at a Publisher and at a Subscriber." (Anthony Sequeira & Brian Alderman, "The SQL Server 2000 Book", 2003)

"Integrating, matching, or linking data from disparate sources." (Linda Volonino & Efraim Turban, "Information Technology for Management" 8th Ed., 2011)

"The continuous harmonization of data attribute values between two or more different systems, with the end result being the data attribute values are the same in all of the systems." (DAMA International, "The DAMA Dictionary of Data Management", 2011)

[initial synchronization:] "The first synchronization for a subscription, during which system tables and other objects that are required by replication, and the schema and data for each article, are copied to the Subscriber." (Microsoft, "SQL Server 2012 Glossary", 2012)

"The process by which a satellite downloads and runs the same DB2 database commands, operating system commands, and SQL statements from the satellite control server as the other members of its group download and then reports the results to the satellite control server." (Sybase, "Open Server Server-Library/C Reference Manual", 2019)

"A form of embedded middleware that allows applications to update data on two systems so that the data sets are identical. These services can run via a variety of different transports but typically require some application-specific knowledge of the context and notion of the data being synchronized." (Gartner)

"Data synchronization is the effort to ensure that, once data leaves a system or storage entity, it does not fall out of harmony with its source, thereby creating inconsistency in the data record." (Information) [source] 

 "1. In replication, the process of data and schema changes being propagated between the Publisher and Subscribers after the initial snapshot has been applied at the Subscriber. 2. In database mirroring, when a mirroring session starts or resumes, the process in which log records of the principal database that have accumulated on the principal server are sent to the mirror server, which writes these log records to disk as quickly as possible to catch up with the principal server." (Microsoft Technet)

"The process of keeping selected data in multiple data sources in agreement." (Microsoft Technet)

"The term, Synchronization, refers to the process of replicating the changes made to documents on one database to the same documents in a second instance of that database." (Couchbase)

🛢DBMS: Two-Phase Commit [2PC] (Definitions)

"An approach for maintaining consistency over multiple systems. In the first phase, all backends are asked to confirm a requested change so that in the second phase the commitment of the updates usually succeeds." (Nicolai M Josuttis, "SOA in Practice", 2007)

"A protocol that ensures that transactions that apply to more than one server are completed on all servers or on none." (Microsoft Corporation, "SQL Server 7.0 System Administration Training Kit", 1999)

"A mechanism to synchronize updates on different machines or platforms, so that they all fall or all succeed together. The decision to commit is centralized, but each participant has the right to veto. This is a key process in real-time, transaction-based environments." (Atul Apte, "Java™ Connector Architecture: Building Custom Connectors and Adapters", 2002)

"A process that ensures transactions that apply to more than one server are completed on all servers or on none." (Anthony Sequeira & Brian Alderman, "The SQL Server 2000 Book", 2003)

"This is a special transaction involving two servers in which the transaction must be applied to both servers, or the entire transaction is rolled back from both servers." (Joseph L Jorden & Dandy Weyn, "MCTS Microsoft SQL Server 2005: Implementation and Maintenance Study Guide - Exam 70-431", 2006)

"A transaction processing protocol that first ensures the transaction holds locks on all records involved before committing any updates." (DAMA International, "The DAMA Dictionary of Data Management", 2011)

"A protocol that ensures that transactions that apply to more than one server are completed on all servers or none at all. Two-phase commit is coordinated by the transaction manager and supported by resource managers." (Microsoft, "SQL Server 2012 Glossary", 2012)

"A two-step process by which recoverable resources and an external subsystem are committed. During the first step, the database manager subsystems are polled to ensure that they are ready to commit. If all subsystems respond positively, the database manager instructs them to commit." (IBM, "Informix Servers 12.1", 2014)

"A mechanism that is another control used in databases to ensure the integrity of the data held within the database." (Adam Gordon, "Official (ISC)2 Guide to the CISSP CBK" 4th Ed., 2015)

"A two-step process by which recoverable resources and an external subsystem are committed. During the first step, the database manager subsystems are polled to ensure that they are ready to commit. If all subsystems respond positively, the database manager instructs them to commit. See also distributed transaction." (Sybase, "Open Server Server-Library/C Reference Manual", 2019)

"A feature of transaction processing systems that enables a database to be returned to the pretransaction state if an error condition occurs." (Craig S Mullins, "Database Administration: The Complete Guide to DBA Practices and Procedures", 2012)

"A process that ensures transactions that apply to more than one server are completed on all servers or on none." (Microsoft Technet)

"An operation that is part of a distributed transaction, under the XA specification. (Sometimes abbreviated as 2PC.) When multiple databases participate in the transaction, either all databases commit the changes, or all databases roll back the changes." (MySQL, "MySQL 8.0 Reference Manual Glossary")

"The process of committing a distributed transaction in two phases. In the first phase, the transaction processor checks that all parts of the transaction can be committed. In the second phase, all parts of the transaction are committed. If any part of the transaction indicates in the first phase that it cannot be committed, the second phase does not occur. ODBC does not support two-phase commits." (Microsoft, "ODBC Glossary")