See Also cardinality, query. 

## semi-consistent read 

 A type of read operation used for UPDATE  statements, that is a combination of READ COMMITTED  and consistent read . When an UPDATE  statement examines a row that is already locked, InnoDB  returns the latest committed version to MySQL so that MySQL can determine whether the row matches the WHERE  condition of the UPDATE . If the row matches (must be updated), MySQL reads the row again, and this time InnoDB  either locks it or waits for a lock on it. This type of read operation can only happen when the transaction has the READ COMMITTED isolation level . 

See Also consistent read, isolation level, READ COMMITTED. 

## SERIALIZABLE 

 The isolation level  that uses the most conservative locking strategy, to prevent any other transactions  from inserting or changing data that was read by this transaction, until it is finished. This way, the same query can be run over and over within a transaction, and be certain to retrieve the same set of results each time. Any attempt to change data that was committed by another transaction since the start of the current transaction, cause the current transaction to wait. 

This is the default isolation level specified by the SQL standard. In practice, this degree of strictness is rarely needed, so the default isolation level for InnoDB  is the next most strict, REPEATABLE READ . See Also ACID, consistent read, isolation level, locking, REPEATABLE READ, transaction. 

## serialized dictionary information (SDI) 

 Dictionary object metadata in serialized form. SDI is stored in JSON  format. 

As of MySQL 8.0.3, SDI is present in all InnoDB  tablespace files except for temporary tablespace and undo tablespace files. The presence of SDI in tablespace files provides metadata redundancy. For example, dictionary object metadata can be extracted from tablespace files using the ibd2sdi  utility if the data dictionary becomes unavailable. 

For a MyISAM  table, SDI is stored in a .sdi  metadata file in the schema directory. An SDI metadata file is required to perform an IMPORT TABLE  operation. 

See Also file-per-table, general tablespace, system tablespace, tablespace. 

## server 

 A type of program that runs continuously, waiting to receive and act upon requests from another program (the client ). Because often an entire computer is dedicated to running one or more server programs (such as a database server, a web server, an application server, or some combination of these), the term server  can also refer to the computer that runs the server software. 

See Also client, mysqld. 

## server-side prepared statement 

 A prepared statement  managed by the MySQL server. Historically, issues with server-side prepared statements led Connector/J  and Connector/PHP  developers to sometimes use client-side prepared statements  instead. With modern MySQL server versions, server-side prepared statements are recommended for performance, scalability, and memory efficiency. 

See Also client-side prepared statement, Connector/J, Connector/PHP, prepared statement. 

## servlet 

See Also Connector/J. 

## session temporary tablespace 

 A temporary tablespace  that stores user-created temporary tables  and internal temporary tables created by the optimizer  when InnoDB  is configured as the on-disk storage engine for internal temporary tables. 

