5 Utilities
The bindings described in this section are provided by the specific
modules below, not by (planet ryanc/db:1:4).
5.1 Connection utilities
5.1.1 Connection pooling
Creating an ordinary connection is often a relatively costly
operation; it may involve steps such as process creation and SSL
negotiation. A connection pool helps reduce connection costs
by reusing connections.
Creates a
connection pool. The pool consists of up to
max-connections, divided between leased connections and up to
max-idle-connections idle connections. The pool uses
connect to create new connections when needed; the
connect function must return a fresh connection each time it
is called.
See also virtual-connection for a mechanism that eliminates
the need to explicitly call connection-pool-lease and
disconnect.
Returns #t if x is a connection pool, #f
otherwise.
Obtains a connection from the connection pool, using an existing idle
connection in pool if one is available. If no idle connection
is available and the pool contains fewer than its maximum allowed
connections, a new connection is created; otherwise an exception is
raised.
Calling disconnect on the connection obtained causes the
connection to be released back to the connection pool. The connection
is also released if release becomes available, if it is a
synchronizable event, or if release is shutdown, if it is a
custodian. The default for release is the current thread, so
the resulting connection is released when the thread that requested it
terminates.
When a connection is released, it is kept as an idle connection if
pool’s idle connection limit would not be exceeded;
otherwise, it is disconnected. If the connection is in a transaction,
the transaction is rolled back.
5.1.2 Virtual connections
A virtual connection creates actual connections on demand and
automatically releases them when they are no longer needed.
Creates a
virtual connection that creates actual connections on
demand using the
connect function, or by calling
(connection-pool-lease connect) if
connect is a
connection pool. A virtual connection encapsulates a mapping
of threads to actual connections. When a query function is called with
a virtual connection, the current thread’s associated actual
connection is used to execute the query. If there is no actual
connection associated with the current thread, one is obtained by
calling
connect. An actual connection is disconnected when
its associated thread dies.
Virtual connections are especially useful in contexts such as web
servlets, where each request is handled in a fresh thread. A single
global virtual connection can be defined, freeing each servlet request
from explicitly opening and closing its own connections. In
particular, a virtual connection backed by a connection
pool combines convenience with efficiency:
The resulting virtual connection leases a connection from the pool on
demand for each servlet request thread and releases it when the thread
terminates (that is, when the request has been handled).
When given a connection produced by virtual-connection,
connected? indicates whether there is an actual connection
associated with the current thread. Likewise, disconnect
causes the current actual connection associated with the thread (if
there is one) to be disconnected, but the connection will be recreated
if a query function is executed.
Connections produced by virtual-connection may not be used
with the prepare function. However, they may still be used to
execute parameterized queries expressed as strings or encapsulated via
virtual-statement.
5.1.3 Kill-safe connections
Creates a proxy for connection
c. All queries performed
through the proxy are kill-safe; that is, if a thread is killed during
a call to a query function such as
query, the connection will
not become locked or damaged. (Connections are normally thread-safe but
not kill-safe.)
Note: A kill-safe connection whose underlying connection uses ports to
communicate with a database server is not protected from a custodian
shutting down its ports.
5.1.4 Data source names
A DSN (Data Source name) is a symbol associated with a
connection specification in a DSN file (inspired by ODBC’s DSNs).
Represents a data source. The
connector field determines
which connection function is used to create the connection. The
args field is a partial list of arguments passed to the
connection function; additional arguments may be added when
dsn-connect is called. The
extensions field
contains additional information about a connection; for example,
this library’s testing framework uses it to store SQL dialect
flags.
Data sources can also be created using the
postgresql-data-source, etc auxiliary functions.
Makes a connection using the connection information associated with
dsn in dsn-file. The given args and
kw-args are added to those specified by dsn to
form the complete arguments supplied to the connect function.
If dsn-file does not exist, or if it contains no entry
for dsn, an exception is raised. If dsn is a
data-source, then dsn-file is ignored.
A parameter holding the location of the default DSN file. The
initial value is a file located immediately within
(find-system-path 'prefs-dir).
Returns the
data-source associated with
dsn in
dsn-file.
If dsn-file does not exist, an exception is raised. If
dsn-file does not have an entry for dsn,
default is called if it is a function or returned
otherwise.
Associates dsn with the given data source ds in
dsn-file, replacing the previous association, if one
exists.
| (postgresql-data-source | | | | [ | #:user user | | | | | #:database database | | | | | #:server server | | | | | #:port port | | | | | #:socket socket | | | | | #:password password | | | | | #:allow-cleartext-password? allow-cleartext-password? | | | | | #:ssl ssl | | | | | #:notice-handler notice-handler | | | | | #:notification-handler notification-handler]) | |
| | → data-source? | | user : string? = absent | | database : string? = absent | | server : string? = absent | | port : exact-positive-integer? = absent | | socket : (or/c path-string? 'guess #f) = absent | | password : (or/c string? #f) = absent | | allow-cleartext-password? : boolean? = absent | | ssl : (or/c 'yes 'optional 'no) = absent | | notice-handler : (or/c 'output 'error) = absent | | notification-handler : (or/c 'output 'error) = absent |
|
|
| (sqlite3-data-source | [ | #:database database | | | | | #:mode mode | | | | | #:busy-retry-limit busy-retry-limit | | | | | #:busy-retry-delay busy-retry-delay]) | |
| | → data-source? | | database : (or/c path-string? 'memory 'temporary) = absent | | mode : (or/c 'read-only 'read/write 'create) = absent | | |
|
| (odbc-data-source | | | | [ | #:dsn dsn | | | | | #:database database | | | | | #:user user | | | | | #:password password | | | | | #:notice-handler notice-handler | | | | | #:strict-parameter-types? strict-parameter-types? | | | | | #:character-mode character-mode]) | |
| | → data-source? | | dsn : (or/c string? #f) = absent | | database : (or/c string? #f) = absent | | user : (or/c string? #f) = absent | | password : (or/c string? #f) = absent | | notice-handler : (or/c 'output 'error) = absent | | strict-parameter-types? : boolean? = absent | | character-mode : (or/c 'wchar 'utf-8 'latin-1) = absent |
|
5.2 Geometric types
The following structures and functions deal with geometric values
based on the OpenGIS (ISO 19125) model.
Note: Geometric columns defined using the PostGIS extension to
PostgreSQL are not directly supported. Instead, data should be
exchanged in the Well-Known Binary format; conversion of the following
structures to and from WKB format is supported by the
wkb->geometry and geometry->wkb functions.
Represents an OpenGIS Point.
Represents an OpenGIS LineString.
Represents an OpenGIS Polygon.
Represents an OpenGIS MultiPoint, a collection of points.
Represents an OpenGIS MultiLineString, a collection of line-strings.
Represents an OpenGIS MultiPolygon, a collection of polygons.
Represents an OpenGIS GeometryCollection, a collection of
arbitrary geometric values.
Returns
#t if
x is a
line-string
consisting of exactly two points (cf OpenGIS
Line);
#f
otherwise.
Returns
#t if
x is a
line-string whose
first and last points are equal (cf OpenGIS
LinearRing);
#f otherwise.
Returns the Well-Known Binary (WKB) encoding of the geometric value
g. The big-endian? argument determines the byte
order used (the WKB format includes byte-order markers, so a robust
client should accept either encoding).
Decodes the Well-Known Binary (WKB) representation of a geometric
value.
5.3 PostgreSQL-specific types
The following structures represent certain of PostgreSQL’s built-in
geometric types that have no appropriate analogue in the OpenGIS
model: box, path, and circle. The point,
lseg, and polygon PostgreSQL built-in types are represented
using point, line-string (line?), and
polygon structures.
Note: PostgreSQL’s built-in geometric types are distinct from those
provided by the PostGIS extension library (see Geometric types).