🛢DBMS: Throughput (Definitions)

"The volume of work completed in a given time period. It is usually measured in transactions per second (TPS)." (Karen Paulsell et al, "Sybase SQL Server: Performance and Tuning Guide", 1996)

"The number of operations the DBMS can do in a time unit." (Peter Gulutzan & Trudy Pelzer, "SQL Performance Tuning", 2002)

"The amount of work performed by a computer system within a specified time interval; for example, the number of transactions of a certain type that can be processed per second. See also response time, workload, channel capacity." (Richard D Stutzke, "Estimating Software-Intensive Systems: Projects, Products, and Processes", 2005)

"Amount of activity a system can sustain over a period of time." (Marilyn Miller-White et al, "MCITP Administrator: Microsoft® SQL Server™ 2005 Optimization and Maintenance 70-444", 2007)

"The amount of data that is transferred from sender to receiver over time." (John Goodson & Robert A Steward, "The Data Access Handbook", 2009)

"The number of work items processed per unit of time." (Max Domeika, "Software Development for Embedded Multi-core Systems", 2011)

"Given a set of tasks to be performed, the rate at which those tasks are completed. Throughput measures the rate of computation, and it is given in units of tasks per unit time." (Michael McCool et al, "Structured Parallel Programming", 2012)

"The amount of work completed in a unit of time." (Oracle, "Database SQL Tuning Guide Glossary", 2013)

"The rate at which transactions are completed in a system." (Marcia Kaufman et al, "Big Data For Dummies", 2013)

🛢DBMS: Savepoint (Definitions)

"A marker that the user includes in a user-defined transaction. When transactions are rolled back, they can be rolled back only to the savepoint." (Microsoft Corporation, "SQL Server 7.0 System Administration Training Kit", 1999)

"A marker that allows an application to roll back part of a transaction if a minor error is encountered. The application must still commit or roll back the full transaction when it is complete." (Anthony Sequeira & Brian Alderman, "The SQL Server 2000 Book", 2003)

"A location to which a transaction can return if part of the transaction is conditionally canceled or encounters an error, hence offering a mechanism to roll back portions of transactions." (SQL Server 2012 Glossary, "Microsoft", 2012)

"A named entity that represents the state of data and schemas at a particular point in time within a unit of work." (Sybase, "Open Server Server-Library/C Reference Manual", 2019)

[nested savepoint] "A savepoint that is included or positioned within another savepoint. Nested savepoints allow an application to have multiple levels of savepoints active at a time and allow the application to roll back to any active savepoint as required." (Sybase, "Open Server Server-Library/C Reference Manual", 2019)

 "A marker that allows an application to roll back part of a transaction if a minor error is encountered." (Microsoft Technet)

"A named SCN in a transaction to which the transaction can be rolled back." (Oracle, "Oracle Database Concepts")

"Savepoints help to implement nested transactions. They can be used to provide scope to operations on tables that are part of a larger transaction. For example, scheduling a trip in a reservation system might involve booking several different flights; if a desired flight is unavailable, you might roll back the changes involved in booking that one leg, without rolling back the earlier flights that were successfully booked." (MySQL, "MySQL 8.0 Reference Manual Glossary")

🛢DBMS: Operational Database [ODB] (Definitions)

"An OLTP database that supports the business operations - for example, logging orders and tracking customers. An operational database is usually the source of data for the data warehouse. Operational data is updated frequently to reflect the current value of all transactions." (Microsoft Corporation, "Microsoft SQL Server 7.0 Data Warehouse Training Kit", 2000)

"A database containing a company's up-to-date and modifiable information." (Glenn J Myatt, "Making Sense of Data: A Practical Guide to Exploratory Data Analysis and Data Mining", 2006)

"A database that is designed primarily to support a company’s day-to-day operations. Also known as a transactional database or production database." (Carlos Coronel et al, "Database Systems: Design, Implementation, and Management" 9th Ed, 2011)

"A database system that runs core functions to the business in production environments. These are not test or reporting database systems, but actual systems that run the operations of the company." (Jason Williamson, Getting a Big Data Job For Dummies, 2015)

"The database of record, consisting of system-specific reference data and event data belonging to a transaction-update system. It may also contain system control data such as indicators, flags and counters. The operational database is the source of data for the data warehouse. It contains detailed data used to run the day-to-day operations of the business. The data continually changes as updates are made, and reflects the current value of the last transaction." (Information Management)

"The database that contains the live data that is viewed, retrieved, and edited in an Oracle Service Cloud application. While reports that are run on the operational database can access real-time data, the reports cannot process as much information as reports that are run on the report database." (Oracle)

"They carry out regular operations of an organisation and are generally very important to a business. They generally use online transaction processing that allows them to enter, collect and retrieve specific information about the company." (Data Floq)

🛢DBMS: Latency (Definitions)

"The amount of time that elapses between when a change is completed on the Publisher and when it appears in the destination database on the Subscriber." (Microsoft Corporation, "SQL Server 7.0 System Administration Training Kit", 1999)

"The amount of time that elapses between when a data change is completed at one server and when that change appears at another." (Anthony Sequeira & Brian Alderman, "The SQL Server 2000 Book", 2003)

"The amount of time that elapses when a data change is completed at one server and when that change appears at another within a replication architecture (for example, the time between when a change is made at a publisher and when it appears at the subscriber)." (Thomas Moore, "MCTS 70-431: Implementing and Maintaining Microsoft SQL Server 2005", 2006)

"The delay in time for a data change to be propagated between nodes in a replication topology." (Marilyn Miller-White et al, "MCITP Administrator: Microsoft® SQL Server™ 2005 Optimization and Maintenance 70-444", 2007)

[latency of information:] "Latency is a time delay between the moment something is initiated and the moment one of its effects begins or becomes detectable. Latency of information applies this concept to changes, updates, and deletes of information." (Allen Dreibelbis et al, "Enterprise Master Data Management", 2008)

[data latency:] "Technically, the speed in which data is captured is referred to as data latency. It is a measure of data 'freshness', specifically data that are less than 24 hours old." (Linda Volonino & Efraim Turban, "Information Technology for Management" 8th Ed., 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 delay that occurs while data is processed or delivered." (Microsoft, "SQL Server 2012 Glossary", 2012)

"In replication, part or all of the approximate difference between the time that a source table is changed and the time that the change is applied to the corresponding target table." (Sybase, "Open Server Server-Library/C Reference Manual", 2019)

 "The amount of time that elapses when a data change is completed at one server and when that change appears at another server." (Microsoft Technet)

🛢DBMS: Kernel (Definitions)

"A module within SQL Server that acts as the interface between SQL Server and the operating system." (Karen Paulsell et al, "Sybase SQL Server: Performance and Tuning Guide", 1996)

"The essential core component of the server that handles several functions, such as task scheduling, disk caching, locking, and executing compiled queries." (Microsoft Corporation, "SQL Server 7.0 System Administration Training Kit", 1999)

"In SQL Server 2000, a subset of the storage engine that is referenced in some error messages. In Windows 2000, the core of the operating system that performs basic operations." (Anthony Sequeira & Brian Alderman, "The SQL Server 2000 Book", 2003)

"A general term for a small section of code that (1) executes a large amount of computation relative to other parts of the program (also known as a hotspot), and/or (2) is the key code sequence for an algorithm." (Michael McCool et al, "Structured Parallel Programming", 2012)

"The part of an operating system that contains programs for such tasks as input/output, management and control of hardware, and the scheduling of user tasks." (IBM, "Informix Servers 12.1", 2014)

"the software which provides controls for hardware devices, manages memory, executes code on the computer's CPU, and hides the details of the underlying physical hardware from user applications." ( Manish Agrawal, "Information Security and IT Risk Management", 2014)

"The core of an operating system, a kernel manages the machine’s hardware resources (including the processor and the memory) and provides and controls the way any other software component accesses these resources." (Shon Harris & Fernando Maymi, "CISSP All-in-One Exam Guide" 8th Ed., 2018)

🛢DBMS: Multidimensional Database (Definitions)

"Database in which the data is presented in data cubes, as opposed to tables in a relational database platform." (Ralph Kimball & Margy Ross, "The Data Warehouse Toolkit" 2nd Ed., 2002)

"A data warehouse design that uses fact tables and dimension tables to organize data efficiently for summarizing large groups of records." (Reed Jacobsen & Stacia Misner, "Microsoft SQL Server 2005 Analysis Services Step by Step", 2006)

"A data structure with three or more independent dimensions." (DAMA International, "The DAMA Dictionary of Data Management", 2011)

"Specialized data store that organizes facts by dimensions, such as geographical region, product line, salesperson, or time." (Linda Volonino & Efraim Turban, "Information Technology for Management" 8th Ed., 2011)

"A database optimized for data online analytical processing (OLAP) applications and for data warehousing." (Analytics Insight)

🛢DBMS: Metadata Repository (Definitions)

 "A database or storage medium where Metadata are stored and easily accessed by people in an organization." (Margaret Y Chu, "Blissful Data ", 2004)

"A centralized database containing metadata captured from around the enterprise." (Sharon Allen & Evan Terry, "Beginning Relational Data Modeling 2nd Ed.", 2005)

"A database where metadata are stored as structured data that can be easily accessed and queried by business and technology workers." (Danette McGilvray, "Executing Data Quality Projects", 2008)

"A container of consistent definitions of business data and rules for mapping data to their actual physical locations in the system." (Judith Hurwitz et al, "Service Oriented Architecture For Dummies" 2nd Ed., 2009)

"A database constructed for the purpose of storing, managing, and making available metadata." (David C Hay, "Data Model Patterns: A Metadata Map", 2010)

"A container of consistent definitions of business data and rules for mapping data to its actual physical locations in the system." (Marcia Kaufman et al, "Big Data For Dummies", 2013) 

"A metadata repository is a software tool or database used to store and manage metadata." (Piethein Strengholt, "Data Management at Scale", 2020)

🛢DBMS: Repository (Definitions)

"The storage container for the metadata managed by OLAP Services. Metadata is stored in tables in a relational database and is used to define the parameters and properties of OLAP server objects." (Microsoft Corporation, "SQL Server 7.0 System Administration Training Kit", 1999)

"A database containing information models that, in conjunction with the executable software, manage the database." (Anthony Sequeira & Brian Alderman, "The SQL Server 2000 Book", 2003)

"A repository is a collection of resources that can be accessed to retrieve information." (S. Sumathi & S. Esakkirajan, "Fundamentals of Relational Database Management Systems", 2007)

"A database for software and components, with an emphasis on revision control and configuration management. Where they keep the good stuff, in other words." (Judith Hurwitz et al, "Service Oriented Architecture For Dummies" 2nd Ed., 2009)

"A database containing information models that, in conjunction with the executable software, manage the database." (Microsoft, "SQL Server 2012 Glossary", 2012)

"A store of information about the data assets of an organization." (Craig S Mullins, "Database Administration", 2012)

"A database for software and components, with an emphasis on revision control and configuration management (where they keep the good stuff, in other words)." (Marcia Kaufman et al, "Big Data For Dummies", 2013)

"A place where important corporate metadata is stored" (Daniel Linstedt & W H Inmon, "Data Architecture: A Primer for the Data Scientist", 2014)

"a database for software and components, with an emphasis on revision control and configuration management (where they keep the good stuff, in other words)." (Judith S Hurwitz, "Cognitive Computing and Big Data Analytics", 2015)

"A storage location for physical data, preferably databases." (Hamid R Arabnia et al, "Application of Big Data for National Security", 2015)

"In a software context, a repository is a data store that contains the code and or data for a project." (Alex Thomas, "Natural Language Processing with Spark NLP", 2020)

"A database containing information models that, in conjunction with the executable software, manage the database." (Microsoft Technet)

🛢DBMS: Database Design (Definitions)

"1.The process of developing a physical data model, followed by definition of all physical database objects, including tables, indexes, and sequences. 2.The physical data model and the detailed DDL for a database. The database design addresses physical constraints such as storage and performance." (DAMA International, "The DAMA Dictionary of Data Management", 2011)

"The process that yields the description of the database structure. The database design process determines the database components. Database design is the second phase of the Database Life Cycle." (Carlos Coronel et al, "Database Systems: Design, Implementation, and Management 9th Ed", 2011)

🛢DBMS: Partitioning (Definitions)

"To divide a table into logical subsets based on characteristics of the data. Partitioning is used to improve application performance or reduce the potential for conflicts in multisite update replication." (Microsoft Corporation, "SQL Server 7.0 System Administration Training Kit", 1999)

"Physically separating data into areas that are more easily maintained or accessed. Data partitioning increases performance and aids in maintenance processes." (Microsoft Corporation, "Microsoft SQL Server 7.0 Data Warehouse Training Kit", 2000)

"The process of splitting a database object (usually a tablespace, table, or index) into two or more physical locations, or partitions, that is, a splitting of a logical group of pages (for example, the pages of a table) into chains or files which are physically removed from each other, perhaps on separate disks. Informix calls this fragmentation." (Peter Gulutzan & Trudy Pelzer, "SQL Performance Tuning", 2002)

"The process of replacing a table with multiple smaller tables. Each smaller table has the same format as the original table, but with a subset of the data. Each partitioned table has rows allocated to it based on some characteristic of the data, such as specific key ranges. The rules that define into which table the rows go must be unambiguous. For example, a table is partitioned into two tables. All rows with primary key values lower than a specified value are allocated to one table, and all keys equal to or greater than the value are allocated to the other. Partitioning can improve application processing speeds and reduce the potential for conflicts in multisite update replication. You can improve the usability of partitioned tables by creating a view. The view, created by a union of select operations on all the partitioned tables, presents the data as if it all resided in a single table." (Anthony Sequeira & Brian Alderman, "The SQL Server 2000 Book", 2003)

"Physical splitting of tables into separate sections (partitions), including parallel processing on multiple partitions and individual operations on individual partitions. One particularly efficient aspect is the capability when querying a table to read fewer than all the partitions making up a table, perhaps even a single partition. This is also known as partition pruning." (Gavin Powell, "Beginning Database Design", 2006)

[data partitioning:] "Process of moving data from a single server to one or more different data repositories. This can be vertical, in which data from a single table is split into multiple tables, or horizontal, in which the number of rows in a table are restricted and partitioned by one or more columns." (Sara Morganand & Tobias Thernstrom , "MCITP Self-Paced Training Kit : Designing and Optimizing Data Access by Using Microsoft SQL Server 2005 - Exam 70-442", 2007)

"The process of replacing a table with multiple smaller units. Tables can be partitioned horizontally or vertically." (Victor Isakov et al, "MCITP Administrator: Microsoft SQL Server 2005 Optimization and Maintenance (70-444) Study Guide", 2007)

"The method for dividing a database into manageable parts for the purpose of easier management and better performance." (Paulraj Ponniah, "Data Warehousing Fundamentals for IT Professionals", 2010)

"The process of splitting a table into subsets of rows or columns." (Carlos Coronel et al, "Database Systems: Design, Implementation, and Management" 9th Ed., 2011)

"The process of replacing a table with multiple smaller tables." (Microsoft, "SQL Server 2012 Glossary,", 2012)

"With respect to distributed databases, partitioning refers to splitting documents, tables, or graphs and distributing them to different servers." (Dan Sullivan, "NoSQL for Mere Mortals®", 2015)

[index-controlled partitioning:] "A type of partitioning in which partition boundaries for a partitioned table are controlled by values that are specified on the CREATE INDEX statement." (Sybase, "Open Server Server-Library/C Reference Manual", 2019)

"Partitioning is the spreading of data across multiple files across a cluster to balance large amounts of data across disks or nodes. Read-only partitions make a read-only table space that prevents updates on all tables in the table space. Other patterns can be applied on this table space to improve performance." (Piethein Strengholt, "Data Management at Scale", 2020)

[composite partitioning:] "In partitioning strategy in which a table is partitioned by one data distribution method and then each partition is further divided into subpartitions using a second data distribution method." (Oracle, "Oracle Database Concepts")

"The ability to decompose very large tables and indexes into smaller and more manageable pieces called partitions." (Oracle, "Oracle Database Concepts")

🛢DBMS: Linked Server (Definitions)

"A definition of an OLE DB data source used by SQL Server distributed queries. The linked server definition specifies the OLE DB provider required to access the data, and includes enough addressing information for the OLE DB provider to connect to the data. Any rowsets exposed by the OLE DB data source can then be referenced as tables, called linked tables, in SQL Server distributed queries." (Microsoft Technet, "Glossary", 0)

"An abstraction of an OLE DB data source that looks like another server to the local SQL Server. A linked server has an associated OLE DB provider that manages the data source. Linked servers allow heterogeneous data access as if the data were local SQL Server data." (Microsoft Corporation, "SQL Server 7.0 System Administration Training Kit", 1999)

"A database object that represents a particular data source and the attributes, including security and collation attributes, necessary to access the data source." (Thomas Moore, "EXAM CRAM™ 2: Designing and Implementing Databases with SQL Server 2000 Enterprise Edition", 2005)

"An OLE DB data source used by SQL Server distributed queries." (Marilyn Miller-White et al, "MCITP Administrator: Microsoft® SQL Server™ 2005 Optimization and Maintenance 70-444", 2007)

"A definition that specifies an external OLE DB database source, such as another SQL Server, or an Oracle server. Once defined, the linked server can be used for distributed queries using only the four-part name in the query." (Darril Gibson, "MCITP SQL Server 2005 Database Developer All-in-One Exam Guide", 2008)

"Database objects that provide the connection information for remote data sources housed on another server. The other server could be a SQL Server, an Oracle server, a Microsoft Access database, or one of many other data sources. Linked servers are created when the remote data source will be accessed more than once or twice." (Robert D. Schneider and Darril Gibson, "Microsoft SQL Server 2008 All-In-One Desk Reference For Dummies", 2008)

"Database objects that provide the connection information for remote data sources housed on another server. The other server could be a SQL Server, an Oracle server, a Microsoft Access database, or one of many other data sources. Linked servers are created when the remote data source will be accessed more than once or twice. See also ad hoc query." (Robert D Schneider & Darril Gibson, "Microsoft SQL Server 2008 All-in-One Desk Reference For Dummies", 2008)

"A definition of an OLE DB data source used by SQL Server distributed queries. The data exposed by a linked server is then referenced as tables, called linked tables." (Jim Joseph, "Microsoft SQL Server 2008 Reporting Services Unleashed", 2009)

"A definition of an OLE DB data source used by SQL Server distributed queries. The linked server definition specifies the OLE DB provider required to access the data, and includes enough addressing information for the OLE DB provider to connect to the data." (Microsoft, "SQL Server 2012 Glossary", 2012)

"This is the remote servers in a distributed query." (Joseph L Jorden & Dandy Weyn, "MCTS Microsoft SQL Server 2005: Implementation and Maintenance Study Guide - Exam 70-431", 2006)

🛢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")

🛢DBMS: Extended Stored Procedure (Definitions)

"A SQL Server-provided procedure that dynamically loads and executes a function within a dynamic link library (DLL) in a manner similar to a stored procedure. Actions outside of SQL Server can be triggered and external information returned to SQL Server. Return status codes and output parameters (identical to their counterparts in regular stored procedures) are also supported." (Microsoft Corporation, "SQL Server 7.0 System Administration Training Kit", 1999)

"A function in a dynamic link library (DLL) that is coded using the SQL Server 2000 Extended Stored Procedure API. The function can then be invoked from Transact-SQL using the same statements that are used to execute Transact- SQL stored procedures." (Anthony Sequeira & Brian Alderman, "The SQL Server 2000 Book", 2003)

"A stored procedure in SQL Server that provides an interface to external COM components (typically DLL files)." (Marilyn Miller-White et al, "MCITP Administrator: Microsoft SQL Server 2005 Optimization and Maintenance 70-444", 2007)

"A function in a dynamic link library (DLL) that is coded using the SQL Server Extended Stored Procedure API. The function can then be invoked from Transact-SQL using the same statements that are used to execute Transact-SQL stored procedures." (Microsoft, "SQL Server 2012 Glossary", 2012)

"Provide a way for SQL Server to add functionality by calling stored procedures. This provides a way to affect external data and to return external data and information to SQL Server." (Owen Williams, "MCSE TestPrep: SQL Server 6.5 Design and Implementation", 1998)

"Extended stored procedures, or XPs, are functions exposed through unmanaged binary DLLs that are designed to run within the SQL Server process space. XPs were used in SQL Server 2000 and prior to programmatically extend the functionality of SQL Server using languages like C and C++ that compile to native code. XPs have been deprecated and SQL CLR functions and procedures are preferred over XPs." (Michael Coles & Rodney Landrum, , "Expert SQL Server 2008 Encryption", 2008)

🛢DBMS: Statistics (Definitions)

"Volatile data about the database, stored in the system catalog so that the optimizer has access to it." (Peter Gulutzan & Trudy Pelzer, "SQL Performance Tuning", 2002)

"Information about tables and indexes stored in the data dictionary used to assist the cost-based optimizer when deciding how to run a given query." (Bob Bryla, "Oracle Database Foundations", 2004)

"SQL Server keeps statistics about the distribution of the key values in each index and uses these statistics to determine what index(es) to use in query processing." (Thomas Moore, "EXAM CRAM™ 2: Designing and Implementing Databases with SQL Server 2000 Enterprise Edition", 2005)

"Information about the distribution of the key values in each index and uses these statistics to determine what index(es) to use in query processing." (Thomas Moore, "MCTS 70-431: Implementing and Maintaining Microsoft SQL Server 2005", 2006)

"Statistics are a small sample of a whole used to represent the whole. In SQL Server, statistics are maintained on indexes and used by the query optimizer to determine which indexes to use for a given query. Instead of scanning an entire index (the entire population), statistical data (a sampling) is maintained on the index." (Darril Gibson, "MCITP SQL Server 2005 Database Developer All-in-One Exam Guide", 2008)

[database statistics:] "In query optimization, refers to measurements about database objects, such as the number of rows in a table, number of disk blocks used, maximum and average row length, number of columns in each row, number of distinct values in each column, etc. Such statistics give a snapshot of database characteristics." (Carlos Coronel et al, "Database Systems: Design, Implementation, and Management" 9th Ed., 2011)

[optimizer statistics:] "Details about the database its object used by the optimizer to select the best execution plan for each SQL statement. Categories include table statistics such as numbers of rows, index statistics such as B-tree levels, system statistics such as CPU and I/O performance, and column statistics such as number of nulls." (Oracle, "Database SQL Tuning Guide Glossary", 2013)

[column statistics:] "Statistics about columns that the optimizer uses to determine optimal execution plans. Column statistics include the number of distinct column values, low value, high value, and number of nulls." (Oracle, "Database SQL Tuning Guide Glossary", 2013)

[index statistics:] "Statistics about indexes that the optimizer uses to determine whether to perform a full table scan or an index scan. Index statistics include B-tree levels, leaf block counts, the index clustering factor, distinct keys, and number of rows in the index." (Oracle, "Database SQL Tuning Guide Glossary", 2013)

"Statistics about tables that the optimizer uses to determine table access cost, join cardinality, join order, and so on. Table statistics include row counts, block counts, empty blocks, average free space per block, number of chained rows, average row length, and staleness of the statistics on the table." (Oracle, "Database SQL Tuning Guide Glossary", 2013)

🛢DBMS: Composite Index (Definitions)

"Indexes which involve more than one column. Use composite indexes when two or more columns are best searched as a unit because of their logical relationship." (Karen Paulsell et al, "Sybase SQL Server: Performance and Tuning Guide", 1996)

"Has two or more columns as index key columns in the same table." (Owen Williams, "MCSE TestPrep: SQL Server 6.5 Design and Implementation", 1998)

"An index that uses more than one column in a table to index data." (Microsoft Corporation, "SQL Server 7.0 System Administration Training Kit", 1999)

[compound index:] "An index whose keys contain values derived from more than one data column." (Peter Gulutzan & Trudy Pelzer, "SQL Performance Tuning", 2002)

"An index that is created on two or more columns in a table." (Bob Bryla, "Oracle Database Foundations", 2004)

"Indexes that can be built on more than a single field." (Gavin Powell, "Beginning Database Design", 2006)

"An index that includes two or more fields." (Rod Stephens, "Beginning Database Design Solutions", 2008)

"An index that is composed of more than one column. Both clustered and nonclustered indexes can be created as composite indexes." (Darril Gibson, "MCITP SQL Server 2005 Database Developer All-in-One Exam Guide", 2008)

"An index that is made of two or more columns." (Robert D. Schneider & Darril Gibson, "Microsoft SQL Server 2008 All-In-One Desk Reference For Dummies", 2008)

"An index that uses more than one column in a table to index data." (Microsoft, "SQL Server 2012 Glossary", 2012)