See Also optimizer, temporary table, temporary tablespace. 

## shared lock 

 A kind of lock  that allows other transactions  to read the locked object, and to also acquire other shared locks on it, but not to write to it. The opposite of exclusive lock . See Also exclusive lock, lock, transaction. 

## shared tablespace 

 Another way of referring to the system tablespace  or a general tablespace . General tablespaces were introduced in MySQL 5.7. More than one table can reside in a shared tablespace. Only a single table can reside in a file-per-table  tablespace. See Also general tablespace, system tablespace. 

## sharp checkpoint 

 The process of flushing  to disk all dirty  buffer pool pages whose redo entries are contained in certain portion of the redo log . Occurs before InnoDB  reuses a portion of a log file; the log files are used in a circular fashion. Typically occurs with write-intensive workloads . See Also dirty page, flush, redo log, workload. 

## shutdown 

 The process of stopping the MySQL server. By default, this process cleans up operations for InnoDB  tables, so InnoDB  can be slow  to shut down, but fast to start up later. If you skip the cleanup operations, it is fast  to shut down but the cleanup must be performed during the next restart. 

The shutdown mode for InnoDB  is controlled by the innodb_fast_shutdown  option. See Also fast shutdown, InnoDB, slow shutdown, startup. 

## slave 

See replica. 

## slow query log 

 A type of log  used for performance tuning of SQL statements processed by the MySQL server. The log information is stored in a file. You must enable this feature to use it. You control which categories of “slow”  SQL statements are logged. For more information, see Section 5.4.5, “The Slow Query Log” . See Also general query log, log. 

## slow shutdown 

 A type of shutdown  that does additional InnoDB  flushing operations before completing. Also known as a clean shutdown . Specified by the configuration parameter innodb_fast_shutdown=0  or the command SET GLOBAL innodb_fast_shutdown=0; . Although the shutdown itself can take longer, that time should be saved on the subsequent startup. 

See Also clean shutdown, fast shutdown, shutdown. 

## snapshot 

 A representation of data at a particular time, which remains the same even as changes are committed  by other transactions . Used by certain isolation levels  to allow consistent reads . See Also commit, consistent read, isolation level, transaction. 

## sort buffer 

 The buffer used for sorting data during creation of an InnoDB  index. Sort buffer size is configured using the innodb_sort_buffer_size  configuration option. 

## source 

 A database server machine in a replication  scenario that processes the initial insert, update, and delete requests for data. These changes are propagated to, and repeated on, other servers known as replicas . See Also replica, replication. 

