## space ID 

 An identifier used to uniquely identify an InnoDB tablespace  within a MySQL instance. The space ID for the system tablespace  is always zero; this same ID applies to all tables within the system tablespace or within a general tablespace. Each file-per-table  tablespace and general tablespace  has its own space ID. 

Prior to MySQL 5.6, this hardcoded value presented difficulties in moving InnoDB  tablespace files between MySQL instances. Starting in MySQL 5.6, you can copy tablespace files between instances by using the transportable tablespace  feature involving the statements FLUSH TABLES ... FOR EXPORT , ALTER TABLE ... DISCARD TABLESPACE , and ALTER TABLE ... IMPORT TABLESPACE . The information needed to adjust the space ID is conveyed in the .cfg file  which you copy along with the tablespace. See Section 15.6.1.3, “Importing InnoDB Tables”  for details. 

See Also .cfg file, file-per-table, general tablespace, .ibd file, system tablespace, tablespace, transportable tablespace. 

## sparse file 

 A type of file that uses file system space more efficiently by writing metadata representing empty blocks to disk instead of writing the actual empty space. The InnoDB transparent page compression  feature relies on sparse file support. For more information, see Section 15.9.2, “InnoDB Page Compression” . 

See Also hole punching, transparent page compression. 

## spin 

 A type of wait  operation that continuously tests whether a resource becomes available. This technique is used for resources that are typically held only for brief periods, where it is more efficient to wait in a “busy loop”  than to put the thread to sleep and perform a context switch. If the resource does not become available within a short time, the spin loop ceases and another wait technique is used. 

See Also latch, lock, mutex, wait. 

## Spring 

 A Java-based application framework designed for assisting in application design by providing a way to configure components. 

See Also J2EE. 

## SQL 

 The Structured Query Language that is standard for performing database operations. Often divided into the categories DDL , DML , and queries . MySQL includes some additional statement categories such as replication . See Chapter 9, Language Structure  for the building blocks of SQL syntax, Chapter 11, Data Types  for the data types to use for MySQL table columns, Chapter 13, SQL Statements  for details about SQL statements and their associated categories, and Chapter 12, Functions and Operators  for standard and MySQL-specific functions to use in queries. 

See Also DDL, DML, query, replication. 

## SQLState 

 An error code defined by the JDBC  standard, for exception handling by applications using Connector/J . 

See Also Connector/J, JDBC. 

## SSD 

 Acronym for “solid-state drive” . A type of storage device with different performance characteristics than a traditional hard disk drive ( HDD ): smaller storage capacity, faster for random reads, no moving parts, and with a number of considerations affecting write performance. Its performance characteristics can influence the throughput of a disk-bound  workload. 

See Also disk-bound, HDD. 

## SSL 

 Acronym for “secure sockets layer” . Provides the encryption layer for network communication between an application and a MySQL database server. 

