Connecting to the Database

With JDBC, a database is represented by a URL (Uniform Resource Locator). With PostgreSQL, this takes one of the following forms:

  • jdbc:postgresql:database
  • jdbc:postgresql:/
  • jdbc:postgresql://host/database
  • jdbc:postgresql://host/
  • jdbc:postgresql://host:port/database
  • jdbc:postgresql://host:port/

The parameters have the following meanings:

  • host

    The host name of the server. Defaults to localhost. To specify an IPv6 address your must enclose the host parameter with square brackets, for example:

    jdbc:postgresql://[::1]:5740/accounting

  • port

    The port number the server is listening on. Defaults to the PostgreSQL™ standard port number (5432).

  • database

    The database name. The default is to connect to a database with the same name as the user name.

To connect, you need to get a Connection instance from JDBC. To do this, you use the DriverManager.getConnection() method:

Connection db = DriverManager.getConnection(url, username, password);

Connection Parameters

In addition to the standard connection parameters the driver supports a number of additional properties which can be used to specify additional driver behaviour specific to PostgreSQL™. These properties may be specified in either the connection URL or an additional Properties object parameter to DriverManager.getConnection. The following examples illustrate the use of both methods to establish a SSL connection.

If a property is specified both in URL and in Properties object, the value from Properties object is ignored.

String url = "jdbc:postgresql://localhost/test";
Properties props = new Properties();
props.setProperty("user","fred");
props.setProperty("password","secret");
props.setProperty("ssl","true");
Connection conn = DriverManager.getConnection(url, props);

String url = "jdbc:postgresql://localhost/test?user=fred&password=secret&ssl=true";
Connection conn = DriverManager.getConnection(url);
  • user = String

    The database user on whose behalf the connection is being made.

  • password = String

    The database user's password.

  • options = String

    Specify 'options' connection initialization parameter. For example setting this to -c statement_timeout=5min would set the statement timeout parameter for this session to 5 minutes.

    The value of this property may contain spaces or other special characters, and it should be properly encoded if provided in the connection URL. Spaces are considered to separate command-line arguments, unless escaped with a backslash (\); \\ represents a literal backslash. ```java props.setProperty("options","-c searchpath=test,public,pgcatalog -c statement_timeout=90000"); Connection conn = DriverManager.getConnection(url, props);

    String url = "jdbc:postgresql://localhost:5432/postgres?options=-c%20searchpath=test,public,pgcatalog%20-c%20statement_timeout=90000"; Connection conn = DriverManager.getConnection(url); ```

  • ssl = boolean

    Connect using SSL. The server must have been compiled with SSL support. This property does not need a value associated with it. The mere presence of it specifies a SSL connection. However, for compatibility with future versions, the value "true" is preferred. For more information see Chapter 4, Using SSL.

    Setting up the certificates and keys for ssl connection can be tricky see The test documentation for detailed examples.

  • sslfactory = String

    The provided value is a class name to use as the SSLSocketFactory when establishing a SSL connection. For more information see the section called “Custom SSLSocketFactory”. defaults to LibPQFactory

  • sslfactoryarg (deprecated) = String

    This value is an optional argument to the constructor of the sslfactory class provided above. For more information see the section called “Custom SSLSocketFactory”.

  • sslmode = String

    possible values include disable, allow, prefer, require, verify-ca and verify-full . require, allow and prefer all default to a non validating SSL factory and do not check the validity of the certificate or the host name. verify-ca validates the certificate, but does not verify the hostname. verify-full will validate that the certificate is correct and verify the host connected to has the same hostname as the certificate. Default is prefer

    Setting these will necessitate storing the server certificate on the client machine see "Configuring the client" for details.

  • sslcert = String

    Provide the full path for the certificate file. Defaults to /defaultdir/postgresql.crt, where defaultdir is ${user.home}/.postgresql/ in *nix systems and %appdata%/postgresql/ on windows.

    It can be a PEM encoded X509v3 certificate

    Note: This parameter is ignored when using PKCS-12 keys, since in that case the certificate is also retrieved from the same keyfile.

  • sslkey = String

    Provide the full path for the key file. Defaults to /defaultdir/postgresql.pk8.

    Note: The key file must be in PKCS-12 or in PKCS-8 DER format. A PEM key can be converted to DER format using the openssl command:

    openssl pkcs8 -topk8 -inform PEM -in postgresql.key -outform DER -out postgresql.pk8 -v1 PBE-MD5-DES

    PKCS-12 key files are only recognized if they have the ".p12" (42.2.9+) or the ".pfx" (42.2.16+) extension.

    If your key has a password, provide it using the sslpassword connection parameter described below. Otherwise, you can add the flag -nocrypt to the above command to prevent the driver from requesting a password.

    Note: The use of -v1 PBE-MD5-DES might be inadequate in environments where high level of security is needed and the key is not protected by other means (e.g. access control of the OS), or the key file is transmitted in untrusted channels. We are depending on the cryptography providers provided by the java runtime. The solution documented here is known to work at the time of writing. If you have stricter security needs, please see https://stackoverflow.com/questions/58488774/configure-tomcat-hibernate-to-have-a-cryptographic-provider-supporting-1-2-840-1 for a discussion of the problem and information on choosing a better cipher suite.

  • sslrootcert = String

    File name of the SSL root certificate. Defaults to defaultdir/root.crt

    It can be a PEM encoded X509v3 certificate

  • sslhostnameverifier = String

    Class name of hostname verifier. Defaults to using org.postgresql.ssl.PGjdbcHostnameVerifier

  • sslpasswordcallback = String

    Class name of the SSL password provider. Defaults to org.postgresql.ssl.jdbc4.LibPQFactory.ConsoleCallbackHandler

  • sslpassword = String

    If provided will be used by ConsoleCallbackHandler

  • protocolVersion = int

    The driver supports the V3 frontend/backend protocols. The V3 protocol was introduced in 7.4 and the driver will by default try to connect using the V3 protocol.

  • loggerLevel = String

    Logger level of the driver. Allowed values: OFF, DEBUG or TRACE. This enable the java.util.logging.Logger Level of the driver based on the following mapping of levels: DEBUG -> FINE, TRACE -> FINEST. This property is intended for debug the driver and not for general SQL query debug.

  • loggerFile = String

    File name output of the Logger. If set, the Logger will use a java.util.logging.FileHandler to write to a specified file. If the parameter is not set or the file can’t be created the java.util.logging.ConsoleHandler will be used instead. This parameter should be use together with loggerLevel.

  • allowEncodingChanges = boolean

    When using the V3 protocol the driver monitors changes in certain server configuration parameters that should not be touched by end users. The client_encoding setting is set by the driver and should not be altered. If the driver detects a change it will abort the connection. There is one legitimate exception to this behaviour though, using the COPY command on a file residing on the server's filesystem. The only means of specifying the encoding of this file is by altering the client_encoding setting. The JDBC team considers this a failing of the COPY command and hopes to provide an alternate means of specifying the encoding in the future, but for now there is this URL parameter. Enable this only if you need to override the client encoding when doing a copy.

  • logUnclosedConnections = boolean

    Clients may leak Connection objects by failing to call its close() method. Eventually these objects will be garbage collected and the finalize() method will be called which will close the Connection if caller has neglected to do this himself. The usage of a finalizer is just a stopgap solution. To help developers detect and correct the source of these leaks the logUnclosedConnections URL parameter has been added. It captures a stacktrace at each Connection opening and if the finalize() method is reached without having been closed the stacktrace is printed to the log.

  • autosave = String

    Specifies what the driver should do if a query fails. In autosave=always mode, JDBC driver sets a savepoint before each query, and rolls back to that savepoint in case of failure. In autosave=never mode (default), no savepoint dance is made ever. In autosave=conservative mode, savepoint is set for each query, however the rollback is done only for rare cases like 'cached statement cannot change return type' or 'statement XXX is not valid' so JDBC driver rollsback and retries

    The default is never

  • cleanupSavepoints = boolean

    Determines if the SAVEPOINT created in autosave mode is released prior to the statement. This is done to avoid running out of shared buffers on the server in the case where 1000's of queries are performed.

    The default is 'false'

  • binaryTransfer = boolean

    Use binary format for sending and receiving data if possible.

    The default is 'true'

  • binaryTransferEnable = String

    A comma separated list of types to enable binary transfer. Either OID numbers or names.

  • binaryTransferDisable = String

    A comma separated list of types to disable binary transfer. Either OID numbers or names. Overrides values in the driver default set and values set with binaryTransferEnable.

  • databaseMetadataCacheFields = int

    Specifies the maximum number of fields to be cached per connection. A value of 0 disables the cache.

    Defaults to 65536.

  • databaseMetadataCacheFieldsMiB = int

    Specifies the maximum size (in megabytes) of fields to be cached per connection. A value of 0 disables the cache.

    Defaults to 5.

  • prepareThreshold = int

    Determine the number of PreparedStatement executions required before switching over to use server side prepared statements. The default is five, meaning start using server side prepared statements on the fifth execution of the same PreparedStatement object. More information on server side prepared statements is available in the section called “Server Prepared Statements”.

  • preparedStatementCacheQueries = int

    Determine the number of queries that are cached in each connection. The default is 256, meaning if you use more than 256 different queries in prepareStatement() calls, the least recently used ones will be discarded. The cache allows application to benefit from “Server Prepared Statements” (see prepareThreshold) even if the prepared statement is closed after each execution. The value of 0 disables the cache.

    N.B.Each connection has its own statement cache.

  • preparedStatementCacheSizeMiB = int

    Determine the maximum size (in mebibytes) of the prepared queries cache (see preparedStatementCacheQueries). The default is 5, meaning if you happen to cache more than 5 MiB of queries the least recently used ones will be discarded. The main aim of this setting is to prevent OutOfMemoryError. The value of 0 disables the cache.

  • preferQueryMode = String

    Specifies which mode is used to execute queries to database: simple means ('Q' execute, no parse, no bind, text mode only), extended means always use bind/execute messages, extendedForPrepared means extended for prepared statements only, extendedCacheEverything means use extended protocol and try cache every statement (including Statement.execute(String sql)) in a query cache. extended | extendedForPrepared | extendedCacheEverything | simple

    The default is extended

  • defaultRowFetchSize = int

    Determine the number of rows fetched in ResultSet by one fetch with trip to the database. Limiting the number of rows are fetch with each trip to the database allow avoids unnecessary memory consumption and as a consequence OutOfMemoryException.

    The default is zero, meaning that in ResultSet will be fetch all rows at once. Negative number is not available.

  • loginTimeout = int

    Specify how long to wait for establishment of a database connection. The timeout is specified in seconds.

  • connectTimeout = int

    The timeout value used for socket connect operations. If connecting to the server takes longer than this value, the connection is broken. The timeout is specified in seconds and a value of zero means that it is disabled.

  • socketTimeout = int

    The timeout value used for socket read operations. If reading from the server takes longer than this value, the connection is closed. This can be used as both a brute force global query timeout and a method of detecting network problems. The timeout is specified in seconds and a value of zero means that it is disabled.

  • cancelSignalTimeout = int

Cancel command is sent out of band over its own connection, so cancel message can itself get stuck. This property controls "connect timeout" and "socket timeout" used for cancel commands. The timeout is specified in seconds. Default value is 10 seconds.

  • tcpKeepAlive = boolean

    Enable or disable TCP keep-alive probe. The default is false.

  • unknownLength = int

    Certain postgresql types such as TEXT do not have a well defined length. When returning meta-data about these types through functions like ResultSetMetaData.getColumnDisplaySize and ResultSetMetaData.getPrecision we must provide a value and various client tools have different ideas about what they would like to see. This parameter specifies the length to return for types of unknown length.

  • stringtype = String

    Specify the type to use when binding PreparedStatement parameters set via setString(). If stringtype is set to VARCHAR (the default), such parameters will be sent to the server as varchar parameters. If stringtype is set to unspecified, parameters will be sent to the server as untyped values, and the server will attempt to infer an appropriate type. This is useful if you have an existing application that uses setString() to set parameters that are actually some other type, such as integers, and you are unable to change the application to use an appropriate method such as setInt().

  • ApplicationName = String

    Specifies the name of the application that is using the connection. This allows a database administrator to see what applications are connected to the server and what resources they are using through views like pgstatactivity.

  • kerberosServerName = String

    The Kerberos service name to use when authenticating with GSSAPI. This is equivalent to libpq's PGKRBSRVNAME environment variable and defaults to "postgres".

  • jaasApplicationName = String

    Specifies the name of the JAAS system or application login configuration.

  • jaasLogin = boolean

    Specifies whether to perform a JAAS login before authenticating with GSSAPI. If set to true (the default), the driver will attempt to obtain GSS credentials using the configured JAAS login module(s) (e.g. Krb5LoginModule) before authenticating. To skip the JAAS login, for example if the native GSS implementation is being used to obtain credentials, set this to false.

  • gssEncMode = String

    PostgreSQL 12 and later now allow GSSAPI encrypted connections. This parameter controls whether to enforce using GSSAPI encryption or not. The options are disable, allow, prefer and require disable is obvious and disables any attempt to connect using GSS encrypted mode allow will connect in plain text then if the server requests it will switch to encrypted mode prefer will attempt connect in encrypted mode and fall back to plain text if it fails to acquire an encrypted connection require attempts to connect in encrypted mode and will fail to connect if that is not possible. The default is allow.

  • gsslib = String

    Force either SSPI (Windows transparent single-sign-on) or GSSAPI (Kerberos, via JSSE) to be used when the server requests Kerberos or SSPI authentication. Permissible values are auto (default, see below), sspi (force SSPI) or gssapi (force GSSAPI-JSSE).

    If this parameter is auto, SSPI is attempted if the server requests SSPI authentication, the JDBC client is running on Windows, and the Waffle libraries required for SSPI are on the CLASSPATH. Otherwise Kerberos/GSSAPI via JSSE is used. Note that this behaviour does not exactly match that of libpq, which uses Windows' SSPI libraries for Kerberos (GSSAPI) requests by default when on Windows.

    gssapi mode forces JSSE's GSSAPI to be used even if SSPI is available, matching the pre-9.4 behaviour.

    On non-Windows platforms or where SSPI is unavailable, forcing sspi mode will fail with a PSQLException.

    To use SSPI with PgJDBC you must ensure that
    [the `waffle-jna` library](https://mvnrepository.com/artifact/com.github.waffle/waffle-jna/)
    

    and its dependencies are present on the CLASSPATH. PgJDBC does not bundle waffle-jna in the PgJDBC jar.

    Since: 9.4

  • sspiServiceClass = String

    Specifies the name of the Windows SSPI service class that forms the service class part of the SPN. The default, POSTGRES, is almost always correct.

    See: SSPI authentication (Pg docs) Service Principal Names (MSDN), DsMakeSpn (MSDN) Configuring SSPI (Pg wiki).

    This parameter is ignored on non-Windows platforms.

  • useSpnego = boolean

    Use SPNEGO in SSPI authentication requests

  • sendBufferSize = int

    Sets SO_SNDBUF on the connection stream

  • receiveBufferSize = int

    Sets SO_RCVBUF on the connection stream

  • readOnly = boolean

    Put the connection in read-only mode

  • readOnlyMode = String

    Controls the behavior when a connection is set to read only, one of 'ignore', 'transaction', or 'always'. When set to 'ignore' then the readOnly setting has no effect. When set to 'transaction' and readOnly is set to 'true' and autocommit is 'false' the driver will set the transaction to readonly by sending BEGIN READ ONLY. When set to 'always' and readOnly is set to 'true' the session will be to READ ONLY if autoCommit is 'true'. If autocommit is false the driver set the transaction to read only by sending BEGIN READ ONLY .

    The default the value is 'transaction'

  • disableColumnSanitiser = boolean

    Setting this to true disables column name sanitiser. The sanitiser folds columns in the resultset to lowercase. The default is to sanitise the columns (off).

  • assumeMinServerVersion = String

    Assume that the server is at least the given version, thus enabling to some optimization at connection time instead of trying to be version blind.

  • currentSchema = String

    Specify the schema (or several schema separated by commas) to be set in the search-path. This schema will be used to resolve unqualified object names used in statements over this connection.

  • targetServerType = String

    Allows opening connections to only servers with required state, the allowed values are any, primary, master, slave, secondary, preferSlave and preferSecondary. The primary/secondary distinction is currently done by observing if the server allows writes. The value preferSecondary tries to connect to secondary if any are available, otherwise allows falls back to connecting also to primary.

    • N.B. the words master and slave are being deprecated. We will silently accept them, but primary and secondary are encouraged.
  • hostRecheckSeconds = int

    Controls how long in seconds the knowledge about a host state is cached in JVM wide global cache. The default value is 10 seconds.

  • loadBalanceHosts = boolean

    In default mode (disabled) hosts are connected in the given order. If enabled hosts are chosen randomly from the set of suitable candidates.

  • socketFactory = String

    The provided value is a class name to use as the SocketFactory when establishing a socket connection. This may be used to create unix sockets instead of normal sockets. The class name specified by socketFactory must extend javax.net.SocketFactory and be available to the driver's classloader. This class must have a zero-argument constructor, a single-argument constructor taking a String argument, or a single-argument constructor taking a Properties argument. The Properties object will contain all the connection parameters. The String argument will have the value of the socketFactoryArg connection parameter.

  • socketFactoryArg (deprecated) = String

    This value is an optional argument to the constructor of the socket factory class provided above.

  • reWriteBatchedInserts = boolean

    This will change batch inserts from insert into foo (col1, col2, col3) values (1,2,3) into insert into foo (col1, col2, col3) values (1,2,3), (4,5,6) this provides 2-3x performance improvement

  • replication = String

Connection parameter passed in the startup message. This parameter accepts two values; "true" and database. Passing true tells the backend to go into walsender mode, wherein a small set of replication commands can be issued instead of SQL statements. Only the simple query protocol can be used in walsender mode. Passing "database" as the value instructs walsender to connect to the database specified in the dbname parameter, which will allow the connection to be used for logical replication from that database.

Parameter should be use together with assumeMinServerVersion with parameter >= 9.4 (backend >= 9.4)

  • escapeSyntaxCallMode = String

    Specifies how the driver transforms JDBC escape call syntax into underlying SQL, for invoking procedures or functions. In escapeSyntaxCallMode=select mode (the default), the driver always uses a SELECT statement (allowing function invocation only). In escapeSyntaxCallMode=callIfNoReturn mode, the driver uses a CALL statement (allowing procedure invocation) if there is no return parameter specified, otherwise the driver uses a SELECT statement. In escapeSyntaxCallMode=call mode, the driver always uses a CALL statement (allowing procedure invocation only).

    The default is select

  • maxResultBuffer = String

    Specifies size of result buffer in bytes, which can't be exceeded during reading result set. Property can be specified in two styles:

    • as size of bytes (i.e. 100, 150M, 300K, 400G, 1T);
    • as percent of max heap memory (i.e. 10p, 15pct, 20percent);

    A limit during setting of property is 90% of max heap memory. All given values, which gonna be higher than limit, gonna lowered to the limit.

    By default, maxResultBuffer is not set (is null), what means that reading of results gonna be performed without limits.

Unix sockets

Aleksander Blomskøld has forked junixsocket and added a Unix SocketFactory that works with the driver. His code can be found at https://github.com/fiken/junixsocket.

Dependencies for junixsocket are :

<dependency>
  <groupId>no.fiken.oss.junixsocket</groupId>
  <artifactId>junixsocket-common</artifactId>
  <version>1.0.2</version>
</dependency>
<dependency>
  <groupId>no.fiken.oss.junixsocket</groupId>
  <artifactId>junixsocket-native-common</artifactId>
  <version>1.0.2</version>
</dependency>

Simply add ?socketFactory=org.newsclub.net.unix.socketfactory.PostgresqlAFUNIXSocketFactory&socketFactoryArg=[path-to-the-unix-socket] to the connection URL.

For many distros the default path is /var/run/postgresql/.s.PGSQL.5432

Connection Fail-over

To support simple connection fail-over it is possible to define multiple endpoints (host and port pairs) in the connection url separated by commas. The driver will try to once connect to each of them in order until the connection succeeds. If none succeed, a normal connection exception is thrown.

The syntax for the connection url is:

jdbc:postgresql://host1:port1,host2:port2/database

The simple connection fail-over is useful when running against a high availability postgres installation that has identical data on each node. For example streaming replication postgres or postgres-xc cluster.

For example an application can create two connection pools. One data source is for writes, another for reads. The write pool limits connections only to a primary node:

jdbc:postgresql://node1,node2,node3/accounting?targetServerType=primary.

And read pool balances connections between secondary nodes, but allows connections also to a primary if no secondaries are available:

jdbc:postgresql://node1,node2,node3/accounting?targetServerType=preferSecondary&loadBalanceHosts=true

If a secondary fails, all secondaries in the list will be tried first. In the case that there are no available secondaries the primary will be tried. If all of the servers are marked as "can't connect" in the cache then an attempt will be made to connect to all of the hosts in the URL in order.

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