python dbpool

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dbpool module

Synopsis

The dbpool module is a wrapper for PythonDB-API 2.0-compliantdatabase modules to (a) keep a pool of physical connections available and (b)upgrade the modules to threadsafety level 2, whichmeans that threads can share logical database connections.

Usage

The module provides only one function not described by theDB-API 2.0spec. The module is initialized by callingset_database with a reference to theunderlying database module to be used and the number of physical databaseconnections to keep in the pool. The dbpool module is thenconfigured to act precisely like the underlying database module, except thatphysical database connections are not always closed when you have finished withthem, and if you try to create more than one cursor on a single logicalconnection, a new physical connection is created for the new cursor.

When a logical database connection is no longer being used (i.e. you callthe close function or all references to the connection aredeleted), the physical connection is returned to the pool to be used the nexttime a connection is requested. If the pool is full (i.e. the limit set in thecall to set_database is reached) thenthe phsyical database connection is closed.

Note that your code can either create one logical database connection, andthen create many cursors from that, or create many logical databaseconnections, and create one or more cursors from each of these. Either way thebehaviour of the dbpool module will be the same - it will poolphsyical database connections, and only create one cursor per physicaldatabase connection.

Example:

import jon.dbpool as dbpool
import MySQLdb, MySQLdb.cursors
dbpool.set_database(MySQLdb, 5)
dbh = dbpool.connect(user="example", passwd="s3cr3t", db="example",
  cursorclass=MySQLdb.cursors.DictCursor)
dbc1 = dbh.cursor()
dbc2 = dbh.cursor()

Note that unfortunately, due to the way the DB-API works, once you haveconfigured dbpool to act as a wrapper for a database module,you cannot re-configure with a different module.

Globals

Variables

apilevel

The string 2.0, indicating the DB-API level.

threadsafety

The integer 2, meaning that threads may shared the module,and database connections.

paramstyle

This variable is only available afterset_database has been called. It willcontain the value from the underlying database module.

Warning

Error

InterfaceError

DatabaseError

DataError

OperationalError

IntegrityError

InternalError

ProgrammingError

NotSupportedError

These exception classes are only available afterset_database has been called. Theyare copied from the underlying database module.

Functions

set_database(dbmod, minconns)

dbmod: module
minconns: integer

Configures the dbpool module to act as a wrapper around thespecified DB-API module. dbmod is a reference to the databasemodule to use. minconns is an integer, which must be 1 or greater,which indicates the number of physical database connections of each 'type' tokeep in the pool. Physical database connections are of the same 'type' if allthe parameters to the DB-API connect function are the same (i.e.they are connecting to the same database, on the same host, with the sameusername, with the same options).

The database module to be used must have a threadsafety levelof at least 1, i.e. if the database cannot cope at all withmulti-threading then there is nothing dbpool can do to make itwork.

Note that you can only call this function once.

Example:

set_database(MySQLdb, 5)

connect(...)

Returns: database connection instance

This function may only be used afterset_database has been called. Theparameters are dependent on the underlying database module being used.A logical database connection from the pool corresponding to databaseconnections with the parameters given is returned. If the pool is empty then anew physical connection is created.

Example:

dbh = dbpool.connect(user="example", passwd="s3cr3t", db="example")
dbc = dbh.cursor()