Then, make the database file read-only. When you open the database now, it is read-only. There are two ways an application can find out whether database is read-only: by calling Connection.

isReadOnly or by executing the SQL statement CALL READONLY. Using the Custom Access Mode r the database can also be opened in read-only mode, even if the database file is not read only. To create a read-only database in a zip file, first create a regular persistent database, and then create a backup. The database must not have pending changes, that means you need to close all connections to the database first. To speed up opening the read-only database and running queries, the database should be closed using SHUTDOWN DEFRAG.

If you are using a database named test , an easy way to create a zip file is using the Backup tool. You can start the tool from the command line, or from within the H2 Console Tools - Backup.

Please note that the database must be closed when the backup is created. Therefore, the SQL statement BACKUP TO can not be used. When the zip file is created, you can open the database in the zip file using the following database URL:. Databases in zip files are read-only. The performance for some queries will be slower than when using a regular database, because random access in zip files is not supported only streaming.

How much this affects the performance depends on the queries and the data. The database is not read in memory; therefore large databases are supported as well. The same indexes are used as when using a regular database. If the database is larger than a few megabytes, performance is much better if the database file is split into multiple smaller files, because random access in compressed files is not possible.

See also the sample application ReadOnlyDatabaseInZip. If a database cannot be opened because the boot info the SQL script that is run at startup is corrupted, then the database can be opened by specifying a database event listener.

The exceptions are logged, but opening the database will continue. Each column is either a base column or a generated column. A generated column is a column whose value is calculated before storing and cannot be assigned directly.

The formula is evaluated when the row is inserted, and re-evaluated every time the row is updated. One use case is to automatically update the last-modification time:. Function indexes are not directly supported by this database, but they can be emulated by using generated columns.

For example, if an index on the upper-case version of a column is required, create a generated column with the upper-case version of the original column, and create an index for this column:. When inserting data, it is not required and not allowed to specify a value for the upper-case version of the column, because the value is generated. But you can use the column when querying the table:. A tool is provided to execute efficient multi-dimension spatial range queries.

This database does not support a specialized spatial index R-Tree or similar. Instead, the B-Tree index is used. For each record, the multi-dimensional key is converted mapped to a single dimensional scalar value. This value specifies the location on a space-filling curve. Currently, Z-order also called N-order or Morton-order is used; Hilbert curve could also be used, but the implementation is more complex. The algorithm to convert the multi-dimensional value is called bit-interleaving.

The scalar value is indexed using a B-Tree index usually using a generated column. The method can result in a drastic performance improvement over just using an index on the first column.

Depending on the data and number of dimensions, the improvement is usually higher than factor 5. The tool generates a SQL query from a specified multi-dimensional range. The method used is not database dependent, and the tool can easily be ported to other databases.

For an example how to use the tool, please have a look at the sample code provided in TestMultiDimension. In addition to the built-in functions, this database supports user-defined Java functions. In this database, Java functions can be used as stored procedures as well. A function must be declared registered before it can be used. A function can be defined using source code, or as a reference to a compiled class that is available in the classpath. By default, the function aliases are stored in the current schema.

When referencing a method, the class must already be compiled and included in the classpath where the database is running. Only static Java methods are supported; both the class and the method must be public. Example Java class:. The Java function must be registered in the database by calling CREATE ALIAS FOR :. When defining a function alias with source code, the database tries to compile the source code using the Java compiler the class javax. getSystemJavaCompiler if it is in the classpath.

If not, javac is run as a separate process. Only the source code is stored in the database; the class is compiled each time the database is re-opened. If you use some third-party script processing tool, use standard single quotes instead and don't forget to repeat each single quotation mark twice within the source code.

By default, the three packages java. util, java. math, java. sql are imported. The method name nextPrime in the example above is ignored. Method overloading is not supported when declaring functions as source code, that means only one method may be declared for an alias.

If different import statements are required, they must be declared at the beginning and separated with the tag CODE :. Multiple methods may be bound to a SQL function if the class is already compiled and included in the classpath. Each Java method must have a different number of arguments. Method overloading is not supported when declaring functions as source code.

Functions that accept non-nullable parameters such as int will not be called if one of those parameters is NULL. Instead, the result of the function is NULL.

If the function should be called if a parameter is NULL , you need to use java. Integer instead. SQL types are mapped to Java classes and vice-versa as in the JDBC API. For details, see Data Types. There are a few special cases: java. Object is mapped to OTHER a serialized object. Therefore, java. Object can not be used to match all SQL types matching all SQL types is not supported.

The second special case is Object[] : arrays of any class are mapped to ARRAY. Objects of type org. Value the internal value class are passed through without conversion. If the first parameter of a Java function is a java. Connection , then the connection to database is provided. This connection does not need to be closed before returning. When calling the method from within the SQL statement, this connection parameter does not need to be can not be specified. If a function throws an exception, then the current statement is rolled back and the exception is thrown to the application.

SQLException are directly re-thrown to the calling application; all other exceptions are first converted to a SQLException. Functions may returns a result set. Such a function can be called with the CALL statement:. A function can create a result set using the SimpleResultSet tool:. A function that returns a result set can be used like a table. However, in this case the function is called at least twice: first while parsing the statement to collect the column names with parameters set to null where not known at compile time.

And then, while executing the statement to get the data maybe multiple times if this is a join. If the function is called just to get the column list, the URL of the connection passed to the function is jdbc:columnlist:connection. Otherwise, the URL of the connection is jdbc:default:connection. For situations where you need to expose other data-sources to the SQL engine as a table, there are "pluggable tables". For some examples, have a look at the code in org.

In order to create your own TableEngine, you need to implement the org. TableEngine interface e. something like this:. In which case the parameters are passed down in the tableEngineParams field of the CreateTableData object.

Params from the schema are used when CREATE TABLE issued on this schema does not have its own engine params specified. This database supports Java triggers that are called before or after a row is updated, inserted or deleted. Triggers can be used for complex consistency checks, or to update related data in the database. It is also possible to use triggers to simulate materialized views. A Java trigger must implement the interface org.

The trigger class must be available in the classpath of the database engine when using the server mode, it must be in the classpath of the server. The connection can be used to query or update data in other tables. The trigger then needs to be defined in the database:. The trigger can be used to veto a change by throwing a SQLException.

As an alternative to implementing the Trigger interface, an application can extend the abstract class org. This will allows to use the ResultSet interface within trigger implementations.

In this case, only the fire method needs to be implemented:. Empty space in the database file re-used automatically. When closing the database, the database is automatically compacted for up to milliseconds by default.

To compact more, use the SQL statement SHUTDOWN COMPACT. However re-creating the database may further reduce the database size because this will re-build the indexes. Here is a sample function to do this:.

See also the sample application org. The database keeps most frequently used data in the main memory. This setting has no effect for in-memory databases. For persistent databases, the setting is stored in the database and re-used when the database is opened the next time. However, when opening an existing database, the cache size is set to at most half the amount of memory available for the virtual machine Runtime. maxMemory , even if the cache size setting stored in the database is larger; however the setting stored in the database is kept.

An experimental scan-resistant cache algorithm "Two Queue" 2Q is available. The cache might not actually improve performance. If you plan to use it, please run your own test cases first. Also included is an experimental second level soft reference cache. Rows in this cache are only garbage collected on low memory. By default the second level cache is disabled. External authentication allows to optionally validate user credentials externally JAAS,LDAP,custom classes.

Is also possible to temporary assign roles to externally authenticated users. This feature is experimental and subject to change. This setting in persisted on the database. H2 is the identifier of the authentication realm see later. External authentication requires to send password to the server. For this reason is works only on local connection or remote over ssl. By default external authentication is performed through JAAS login interface configuration name is h2.

To configure JAAS add argument -Djava. conf Here an example of JAAS login configuration file content:. Is it possible to specify custom authentication settings by using JVM argument -Dh2auth.

Here an example of h2auth. xml file content:. Custom credentials validators must implement the interface org. Custom criteria for role assignments must implement the interface org. Window functions Collation support, including support for the ICU4J library Support for users and roles Compatibility modes for IBM DB2, Apache Derby, HSQLDB, MS SQL Server, MySQL, Oracle, and PostgreSQL. Mixed Mode The mixed mode is a combination of the embedded and the server mode.

Database URL Overview This database supports multiple connection modes and connection settings. In-Memory Databases For certain use cases for example: rapid prototyping, testing, high performance operations, read-only databases , it may not be required to persist data, or persist changes to the data.

Database Files Encryption The database files can be encrypted. Three encryption algorithms are supported: "AES" - also known as Rijndael, only AES is implemented. Creating a New Database with File Encryption By default, a new database is automatically created if it does not exist yet when the embedded url is used. Connecting to an Encrypted Database The encryption algorithm is set in the database URL, and the file password is specified in the password field, before the user password.

getConnection url, user, pwds ; Encrypting or Decrypting a Database To encrypt an existing database, use the ChangeFileEncryption tool. jar org. ChangeFileEncryption -dir ~ -db test -cipher AES -encrypt filepwd Database File Locking Whenever a database is opened, a lock file is created to signal other processes that the database is in use.

The following file locking methods are implemented: The default method is FILE and uses a watchdog thread to protect the database file. The watchdog reads the lock file each second.

The second method is SOCKET and opens a server socket. The socket method does not require reading the lock file every second. The socket method should only be used if the database files are only accessed by one and always the same computer. The third method is FS. This will use native file locking using FileChannel. It is also possible to open the database without file locking; in this case it is up to the application to protect the database files.

Failing to do so will result in a corrupted database. Using the method NO forces the database to not create a lock file at all.

Please note that this is unsafe as another process is able to open the same database, possibly leading to data corruption. Opening a Database Only if it Already Exists By default, when an application calls DriverManager. Don't Close a Database when the VM Exits By default, a database is closed when the last connection is closed. sql'"; Please note the double backslash is only required in a Java or properties file.

Ignore Unknown Settings Some applications for example OpenOffice. Changing Other Settings when Opening a Connection In addition to the settings already described, other database settings can be passed in the database URL. Custom File Access Mode Usually, the database opens the database file with the access mode rw , meaning read-write except for read only databases, where the mode r is used.

Multiple Connections Opening Multiple Databases at the Same Time An application can open multiple databases at the same time, including multiple connections to the same database.

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The MySQL server maintains many system variables that configure its operation. Each system variable has a default value. System variables can be set at server startup using options on the command line or in an option file. Most of them can be changed dynamically at runtime using the SET statement, which enables you to modify operation of the server without having to stop and restart it. You can also use system variable values in expressions.

Setting a session system runtime variable value normally requires no special privileges and can be done by any user, although there are exceptions.

For more information, see Section 5. To see the values that a server uses based on its compiled-in defaults and any option files that it reads, use this command:. To see the values that a server uses based only on its compiled-in defaults, ignoring the settings in any option files, use this command:.

To see the current values used by a running server, use the SHOW VARIABLES statement or the Performance Schema system variable tables. See Section This section provides a description of each system variable. For a system variable summary table, see Section 5. For more information about manipulation of system variables, see Section 5. Section 5. Information on tuning system variables can be found in Section 5.

Section For information on server system variables specific to replication, see Section These variables can be enabled with the SET statement by setting them to ON or 1 , or disabled by setting them to OFF or 0. Boolean variables can be set at startup to the values ON , TRUE , OFF , and FALSE not case-sensitive , as well as 1 and 0.

See Section 4. Some system variables control the size of buffers or caches. For a given buffer, the server might need to allocate internal data structures. These structures typically are allocated from the total memory allocated to the buffer, and the amount of space required might be platform dependent. This means that when you assign a value to a system variable that controls a buffer size, the amount of space actually available might differ from the value assigned.

In some cases, the amount might be less than the value assigned. It is also possible that the server adjusts a value upward. For example, if you assign a value of 0 to a variable for which the minimal value is , the server sets the value to Values for buffer sizes, lengths, and stack sizes are given in bytes unless otherwise specified.

Some system variables take file name values. Unless otherwise specified, the default file location is the data directory if the value is a relative path name. To specify the location explicitly, use an absolute path name. If the value is an absolute path name, its location is as given by the path name. Whether to enable automatic activation of all granted roles when users log in to the server:. This takes precedence over default roles specified with SET DEFAULT ROLE. To change the active roles within a session, use SET ROLE.

To change the active roles for a stored program, the program body should execute SET ROLE. If this variable is not specified at startup, the server maintains no administrative interface. See Section 5. The value must be a single IPv4 address, IPv6 address, or host name.

As of MySQL 8. An IP address can be specified as an IPv4 or IPv6 address. If the value is a host name, the server resolves the name to an IP address and binds to that address. If a host name resolves to multiple IP addresses, the server uses the first IPv4 address if there are any, or the first IPv6 address otherwise. For example, if the server is bound to ::ffff A network namespace can be specified for an IP address or a host name. For a given address, the network namespace is optional.

The global namespace is therefore the default. The host system must support network namespaces and each named namespace must previously have been set up. Naming a nonexistent namespace produces an error. For additional information about network namespaces, see Section 5. If binding to the address fails, the server produces an error and does not start. Setting this variable to 0 causes the default value to be used. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

Support for the TLSv1 and TLSv1. The protocols were deprecated from MySQL 8. See Removal of Support for the TLSv1 and TLSv1. Support for the TLSv1. The server checks the version of OpenSSL at startup, and if it is lower than 1. This variable is used to administer multifactor authentication MFA capabilities.

That is, it controls which factors are required or permitted. A warning does occur for statements that otherwise would not be permitted. Exception: Element 1 cannot be empty or missing. In all cases, an element may be surrounded by whitespace characters and the entire list is enclosed in single quotes. The type of value specified for element N in the list has implications for whether factor N must be present in account definitions, and which authentication plugins can be used:. If element N is an authentication plugin name, an authentication method for factor N is required and must use the named plugin.

In addition, the plugin becomes the default plugin for factor N authentication methods that do not name a plugin explicitly. For details, see The Default Authentication Plugin. Authentication plugins that use internal credentials storage can only be specified for the first element and cannot repeat.

For example, the following settings are not permitted:. It may use any authentication plugin that is valid for element N as described later. If element N is empty, an authentication method for factor N is optional.

If given, it may use any authentication plugin that is valid for element N as described later. In this case, such statements cannot specify authentication for factors 2 or 3. Element 1 must name a plugin that does not require a registration step. Elements 2 and 3 must name a plugin that does not use internal credentials storage.

For information about which authentication plugins use internal credentials storage, see Section 6. For factor 1, account definitions can use any plugin. Default authentication plugin rules apply for authentication specifications that do not name a plugin. See The Default Authentication Plugin. For factors 2 and 3, account definitions cannot name a plugin that uses internal credentials storage. For factor 1, this does not apply because element 1 cannot be empty.

Empty elements must occur at the end of the list, following a nonempty element. In other words, the first element cannot be empty, and either no element is empty or the last element is empty or the last two elements are empty.

For example, a value of ',,' is not permitted because it would signify that all factors are optional. That cannot be; accounts must have at least one authentication factor.

This means that factor 1 is required in account definitions and can use any authentication plugin, and that factors 2 and 3 are optional and each can use any authentication plugin that does not use internal credentials storage.

See Section 6. This variable sets the logging level for the Windows authentication plugin. The following table shows the permitted values. A client that authenticates using the InitSecurityContext function should provide a string identifying the service to which it connects targetName. MySQL uses the principal name UPN of the account under which the server is running. This UPN is sent by the server at the beginning of authentication handshake.

This variable controls whether the server sends the UPN in the initial challenge. By default, the variable is enabled. For security reasons, it can be disabled to avoid sending the server's account name to a client as cleartext.

If the variable is disabled, the server always sends a 0x00 byte in the first challenge, the client does not specify targetName , and as a result, NTLM authentication is used. If the server fails to obtain its UPN which happens primarily in environments that do not support Kerberos authentication , the UPN is not sent by the server and NTLM authentication is used. The autocommit mode.

Note that the -Xms option sets both the minimum and the initial heap size of the heap. In Python, all classes are themselves instances of other classes. If the value is 0, timeouts are not enabled. For certain use cases for example: rapid prototyping, testing, high performance operations, read-only databases , it may not be required to persist data, or persist changes to the data. Querying statistics columns does not store or update statistics in the mysql.

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