6.1 Local Sockets for PostgreSQL and MySQL Servers🔗ℹ

PostgreSQL and MySQL servers are sometimes configured by default to listen only on local sockets (also called “unix domain sockets”). This library provides support for communication over local sockets on Linux and Mac OS. If local socket communication is not available, the server must be reconfigured to listen on a TCP port.

The socket file for a PostgreSQL server is located in the directory specified by the unix_socket_directory variable in the postgresql.conf server configuration file. For example, on Ubuntu 11.04 running PostgreSQL 8.4, the socket directory is /var/run/postgresql and the socket file is /var/run/postgresql/.s.PGSQL.5432. Common socket paths may be searched automatically using the postgresql-guess-socket-path function.

The socket file for a MySQL server is located at the path specified by the socket variable in the my.cnf configuration file. For example, on Ubuntu 11.04 running MySQL 5.1, the socket is located at /var/run/mysqld/mysqld.sock. Common socket paths for MySQL can be searched using the mysql-guess-socket-path function.

6.2 PostgreSQL Database Character Encoding🔗ℹ

In most cases, a database’s character encoding is irrelevant, since the connect function always requests translation to Unicode (UTF-8) when creating a connection. If a PostgreSQL database’s character encoding is SQL_ASCII, however, PostgreSQL will not honor the connection encoding; it will instead send untranslated octets, which will cause corrupt data or internal errors in the client connection.

To convert a PostgreSQL database from SQL_ASCII to something sensible, pg_dump the database, recode the dump file (using a utility such as iconv), create a new database with the desired encoding, and pg_restore from the recoded dump file.

6.3 PostgreSQL Authentication🔗ℹ

Changed in version 1.2 of package db-lib: Added SCRAM-SHA-256 support.
Changed in version 1.7: Added SCRAM-SHA-256-PLUS support.
Changed in version 1.12: Added OAUTHBEARER support.

6.4 PostgreSQL Timestamps and Time Zones🔗ℹ

PostgreSQL’s timestamp with time zone type is inconsistent with the SQL standard (probably), inconsistent with time with time zone, and potentially confusing to PostgreSQL newcomers.

A time with time zone is essentially a time structure with an additional field storing a time zone offset. In contrast, a timestamp with time zone has no fields beyond those of timestamp. Rather, it indicates that its datetime fields should be interpreted as a UTC time. Thus it represents an absolute point in time, unlike timestamp without time zone, which represents local date and time in some unknown time zone (possibly—hopefully—known the the database designer, but unknown to PostgreSQL).

When a timestamp with time zone is created from a source without time zone information, the session’s TIME ZONE setting is used to adjust the source to UTC time. When the source contains time zone information, it is used to adjust the timestamp to UTC time. In either case, the time zone information is discarded and only the UTC timestamp is stored. When a timestamp with time zone is rendered as text, it is first adjusted to the time zone specified by the TIME ZONE setting (or by AT TIME ZONE) and that offset is included in the rendered text.

This library receives timestamps in binary format, so the time zone adjustment is not applied, nor is the session’s TIME ZONE offset included; thus all sql-timestamp values in a query result have a tz field of 0 (for timestamp with time zone) or #f (for timestamp without time zone). (Ancient versions of this library sent and received timestamps as text, so they received timestamps with adjusted time zones.)

6.5 MySQL Authentication🔗ℹ

As of version 5.5.7, MySQL supports authentication plugins. This library supports the following plugins:

• caching_sha2_password: the default since MySQL version 8.0

• mysql_native_password: the default for MySQL versions since 4.1 and before 8.0

• mysql_old_password: the default before MySQL version 4.1

• mysql_clear_password: used by LDAP and PAM authentication

See also Making Database Connections Securely.

Changed in version 1.6 of package db-lib: Added support for caching_sha2_password authentication.

6.6 MySQL Connection Character Set🔗ℹ

Warning: If the client, connection, or result character sets are changed (for example, using SET NAMES) to a character set other than UTF-8, errors or data corruption may occur. Note that non-UTF-8 character sets attached to databases, tables, and columns do not cause problems; the server automatically translates between character set used for storage and the one used for communication.

6.7 MySQL CALLing Stored Procedures🔗ℹ

MySQL CALL statements can be executed only if they return at most one result set and contain no OUT or INOUT parameters.

6.8 Cassandra Authentication🔗ℹ

Cassandra, like MySQL, supports authentication plugins. The only plugins currently supported by this library are AllowAllAuthenticator and PasswordAuthenticator.

6.9 SQLite Requirements🔗ℹ

SQLite support requires the appropriate native library.

• On Windows, the library is sqlite3.dll. It is included in the Racket distribution.

• On Mac OS, the library is libsqlite3.0.dylib, which is included (in /usr/lib) in Mac OS version 10.4 onwards.

• On Linux, the library is libsqlite3.so.0. It is included in the libsqlite3-0 package in Debian/Ubuntu and in the sqlite package in Red Hat.

6.10 FFI-Based Connections and Concurrency🔗ℹ

Wire-based connections communicate using ports, which do not cause other Racket threads to block. In contrast, an FFI call causes all Racket threads to block until it completes, so FFI-based connections can degrade the interactivity of a Racket program, particularly if long-running queries are performed using the connection.

This problem can be avoided by creating the FFI-based connection in a separate place using the #:use-place keyword argument. Such a connection will not block all Racket threads during queries; the disadvantage is the cost of creating and communicating with a separate place. On Racket CS, another solution is to execute queries in a separate OS thread; this solution may have lower time and memory overhead than the separate place.

6.11 ODBC Requirements🔗ℹ

ODBC requires the appropriate driver manager native library as well as driver native libraries for each database system you want use ODBC to connect to.

• On Windows, the driver manager is odbc32.dll, which is included automatically with Windows.

• On Mac OS, the driver manager is libiodbc.2.dylib (iODBC), which is included (in /usr/lib) in Mac OS version 10.2 onwards.

• On Linux, the driver manager is libodbc.so.{2,1} (unixODBC—iODBC is not supported). It is available from the unixodbc package in Debian/Ubuntu and in the unixODBC package in Red Hat.

In addition, you must install the appropriate ODBC Drivers and configure Data Sources. Refer to the ODBC documentation for the specific database system for more information.

6.12 ODBC Status🔗ℹ

ODBC support is experimental. The behavior of ODBC connections can vary widely depending on the driver in use and even the configuration of a particular data source.

The following sections describe the configurations that this library has been tested with. Unless otherwise specified, tests were run on Ubuntu 22.04.5 on x86_64 with unixODBC 2.3.9. Reports of success or failure on other platforms or with other drivers would be appreciated.

6.13 Multi-Statement Queries🔗ℹ