Database Connection Pooling With

c3p0By Kasun Dinesh Madusanke

hSenid Lanka: Connection Pooling With c3p0

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Topics What is a Connection?

What is a Connection Pool?

How Connection Pool Works?

Connection Life Cycle

Connection Poolers

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Topics Cont.

Introduction to c3p0

Using c3p0

Configuring c3p0

Benefits of Connection Pooling

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What is a Connection?• In computer science, a database connection is the means by which a database server and

its client software communicate with each

other.

• The term is used whether or not the client and the server are on different machines.

• Connections are built by supplying an underlying driver or provider with a

connection string.

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What is a Connection? Cont.

• Connection string is used to address a specific database or server and to provide instance and

user authentication credentials.

• Connections are a key concept in data-centric programming.

• Since some DBMSs require considerable time to connect, connection pooling is used to improve

performance.

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What is a Connection Pool?

• Database connections are finite and expensive and can take a long time to create relative to

the operations performed on them.

• It is very inefficient for an application to create and close a database connection whenever

it needs to update a database.

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• The application server maintains a pool of ready to use connections to a data store.

o Application client requests a connections using a data source or a connection factory object.

o Connection is retrieved from the pool.

• Opening a connection only when needed, and

closing it as soon as the work is done, rather

than holding a connection open for the entire

life of the application.

What is a Connection Pool? Cont.

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• In this manner, a relatively small number of connections can service a large number of requests.

• Using too many connections may just cause thrashing rather than get more useful work done.

• It is desirable to set some limit on the number of connections in the pool.

• In case all the connections are in use, the operation can block until a connection is returned to the pool, or an

error may be returned.

What is a Connection Pool? Cont.

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How Connection Pool Works?

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Connection Life Cycle• A managed connection object is always in one of three states.

DoesNotExist, InFreePool or InUse

• After a connection is created, it can be in

either,o InUse (if allocated to an application)o InFreePool state

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Connection Life Cycle Cont.

• Between these three states are transitions. Examaple: If the application has called the data

source or connection factory getConnection()

method:

FreePoolState -> InUse state

• After a connection is closed with the close() method, it is either,

o Returned to the free pool

o Destroyed

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Connection Poolers• Here are some of the connection poolers that we can use to create a pool of connections,

o Apache DBCP - Java Database Connection Pooling library

o BoneCP - The JDBC Connection Pool

o MongoPool - Manages MongoDB Connections

o SQL Relay - Database Connection Pool library with API available in all programming languages

o c3p0 - JDBC3 Connection and Statement Pooling

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Introduction to C3P0• c3p0 is an easy-to-use library for augmenting traditional (DriverManager-based) JDBC drivers,

including DataSources that implement Connection and

Statement Pooling.

• In particular, c3p0 provides several useful services:

• A class which adapt traditional DriverManager-based JDBC drivers to the newer javax.sql.DataSource scheme for acquiring database Connections.

• Transparent pooling of Connection and PreparedStatements behind DataSources.

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Using c3p0Creating/initialize a pooled data source

• There are three ways to create a c3p0 connection

pool.

i. Using a ComboPooledDataSource.

ii. DataSources factory class.

iii.Build our own pool-backed DataSource by directly

instantiating PoolBackedDataSource and setting its

ConectionPoolDataSource.

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Using c3p0 Cont.1. Using the ComboPooledDataSource

Most user prefer using this method than the other methods.

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Using c3p0 Cont.2. Using the DataSources factory class

• We can use the static factory class

com.mchange.v2.c3p0.DataSources to build unpooled DataSources

from traditional JDBC drivers, and to build pooled

DataSources from unpooled DataSources.

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Using c3p0 Cont.

We can programmatically set the configuration parameters and

override the default parameters using map like in the code

above.

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Using c3p0 Cont.Querying a PooledDataSource's current status

• Here are some of the methods that we can use to query/get the

information of the current status of the data sources. public int getNumConnectionsDefaultUser() public int getNumIdleConnectionsDefaultUser() public int getNumBusyConnectionsDefaultUser() public int getNumConnections(String username, String

password) public int getNumConnectionsAllUsers()

c3p0 maintains separate pools for Connections withdistinct authentications.

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Using c3p0 Cont.Cleaning up PooledDataSources

o Using destroy method

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Using c3p0 Cont.Cleaning up PooledDataSources Cont.o Using close method

Unreferenced instances of PooledDataSource that are not closed by clients

close() themselves prior to garbage collection in their finalize() methods.

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Configuring c3p0• There are several ways to modify c3p0 properties: By changing the property values associated with a

particular DataSource in your code, or you can configure

c3p0 externally,i. via a simple Java properties file

ii.via HOCON (typesafe-config) files (if and only if

you bundle the typesafe-config library with your

application)

iii.via an XML configuration file

iv.via System properties

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Configuring c3p0 Cont.

• DataSources must be configured before they are used (during or after the construction), c3p0 does support

property modifications midstream.

However if you obtain a DataSource by instantiating a

ComboPooledDataSource, configure it by simply calling

appropriate setter methods offered by that class before

attempting a call to getConnection().

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Configuring c3p0 Cont.

If you obtain a DataSource by using factory methods of

the utility class com.mchange.v2.c3p0.DataSources, and

wish to use a non-default configuration, you can supply

a Map of property names.

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• To override the library's built-in defaults, create a file called

c3p0.properties and place it at the "root" of your classpath or

classloader.

• The file must be available as a classloader resource under the name

/c3p0.properties, in the classloader that loaded c3p0's jar file.

• The format of c3p0.properties should be a normal Java Properties

file format, whose keys are c3p0 configurable properties.An example

c3p0.properties file is given in the next slide.

Configuring c3p0 Cont.Overriding c3p0 defaults via c3p0.properties

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Configuring c3p0 Cont.

• Sample properties file

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Configuring c3p0 Cont.

• HOCON (Human-Optimized Config Object Notation) is a format

for human-readable data, and a superset of JSON.

• You must specify ordinary config params explicitly inside a

c3p0 scope one way or another, even in a c3p0.conf file. "Dot

notation" can be used equivalently to scopes.

Overriding c3p0 defaults with "HOCON“ configuration files

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Configuring c3p0 Cont.Overriding c3p0 defaults with "HOCON“ configuration files Cont.

• HOCON file

• properties file

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Configuring c3p0 Cont.

• You can use the XML config file for all c3p0 configuration,

including configuration of defaults, named configurations,

per-user overrides, and configuration extensions.

• By default, c3p0 will look for an XML configuration file in

its classloader's resource path under the name "/c3p0-

config.xml".

Overriding c3p0 defaults via c3p0-config.xml

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Configuring c3p0 Cont.Overriding c3p0 defaults via c3p0-config.xml Cont.

• Xml configuration file

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Configuring c3p0 Cont.Overriding c3p0 defaults via c3p0-config.xml Cont.

• Xml configuration filewith Named configuration

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Configuring c3p0 Cont.

• c3p0 properties can also be defined as System properties,

using the same "c3p0." prefix for properties specified in a

c3p0.properties file.

Overriding c3p0 defaults with System properties

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Configuring c3p0 Cont.

• Under some circumstances, statement pooling can dramatically

improve application performance.

• Whether and how much statement pooling will help depends on

how much parsing, planning, and optimizing of queries your

databases does when the statements are prepared.

Configuring Statement Pooling

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Configuring c3p0 Cont.

• We can configure statement pooling in c3p0 via the following configuration parameters:

• maxStatements-Defines the total number PreparedStatements a DataSource will cache.

• maxStatementsPerConnection-Defines how many statements each pooled Connection is allowed to own.

• statementCacheNumDeferredCloseThreads-If greater than zero, the Statement pool will defer physically closing cached Statements until its parent Connection is not in use by any client or internally by the pool itself.

Configuring Statement Pooling Cont.

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Configuring c3p0 Cont.

• c3p0 DataSources are designed (and configured by default) to

recover from temporary database outages, such as those which

occur during a database restart or brief loss of network

connectivity.

• You can affect how c3p0 handles errors in acquiring

Connections via the configurable properties described in the

next slide.

Configuring Recovery From Database Outages

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Configuring c3p0 Cont.

• acquireRetryAttempts-How much attempts to get a connection, default

is infinite.

• acquireRetryDelay-Delay between retry attempts.

• breakAfterAcquireFailure-If 'true', DataSource will consider itself

broken after a failed round of Connection

attempts, and future client requests

will fail immediately.

Configuring Recovery From Database Outages Cont.

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Benefits of Connection Pooling• Performance-The connection cost is paid for once and amortized across all the consuming components.

• Diagnostics-If you have one sub-system responsible for connecting to the database, it becomes easier to diagnose and

analyze database connection usage.

• Maintainability-Again, if you have one sub-system responsible for handing out database connections, your code will be

easier to maintain than if each component connected to the

database itself.

Thank You!

By Kasun Dinesh Madusanke

hSenid Lanka: Connection Pooling With c3p0