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<title>Class: ActiveRecord::ConnectionAdapters::ConnectionPool</title>
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<td><strong>Class</strong></td>
<td class="class-name-in-header">ActiveRecord::ConnectionAdapters::ConnectionPool</td>
</tr>
<tr class="top-aligned-row">
<td><strong>In:</strong></td>
<td>
<a href="../../../files/lib/active_record/connection_adapters/abstract/connection_pool_rb.html">
lib/active_record/connection_adapters/abstract/connection_pool.rb
</a>
<br />
</td>
</tr>
<tr class="top-aligned-row">
<td><strong>Parent:</strong></td>
<td>
Object
</td>
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<div id="contextContent">
<div id="description">
<p>
Connection pool base class for managing ActiveRecord database connections.
</p>
<h2>Introduction</h2>
<p>
A <a href="ConnectionPool.html#M000354">connection</a> pool synchronizes
thread access to a limited number of database connections. The basic idea
is that each thread checks out a database <a
href="ConnectionPool.html#M000354">connection</a> from the pool, uses that
<a href="ConnectionPool.html#M000354">connection</a>, and checks the <a
href="ConnectionPool.html#M000354">connection</a> back in. <a
href="ConnectionPool.html">ConnectionPool</a> is completely thread-safe,
and will ensure that a <a href="ConnectionPool.html#M000354">connection</a>
cannot be used by two threads at the same time, as long as <a
href="ConnectionPool.html">ConnectionPool</a>‘s contract is correctly
followed. It will also handle cases in which there are more threads than
connections: if all connections have been checked out, and a thread tries
to <a href="ConnectionPool.html#M000361">checkout</a> a <a
href="ConnectionPool.html#M000354">connection</a> anyway, then <a
href="ConnectionPool.html">ConnectionPool</a> will wait until some other
thread has checked in a <a
href="ConnectionPool.html#M000354">connection</a>.
</p>
<h2>Obtaining (checking out) a <a href="ConnectionPool.html#M000354">connection</a></h2>
<p>
Connections can be obtained and used from a <a
href="ConnectionPool.html#M000354">connection</a> pool in several ways:
</p>
<ol>
<li>Simply use <a href="../Base.html#M000558">ActiveRecord::Base.connection</a>
as with ActiveRecord 2.1 and earlier (pre-<a
href="ConnectionPool.html#M000354">connection</a>-pooling). Eventually,
when you‘re done with the <a
href="ConnectionPool.html#M000354">connection</a>(s) and wish it to be
returned to the pool, you call
ActiveRecord::Base.clear_active_connections!. This will be the default
behavior for ActiveRecord when used in conjunction with ActionPack‘s
request handling cycle.
</li>
<li>Manually check out a <a href="ConnectionPool.html#M000354">connection</a>
from the pool with <a
href="../Base.html#M000565">ActiveRecord::Base.connection_pool</a>.<a
href="ConnectionPool.html#M000361">checkout</a>. You are responsible for
returning this <a href="ConnectionPool.html#M000354">connection</a> to the
pool when finished by calling <a
href="../Base.html#M000565">ActiveRecord::Base.connection_pool</a>.<a
href="ConnectionPool.html#M000362">checkin</a>(<a
href="ConnectionPool.html#M000354">connection</a>).
</li>
<li>Use <a
href="../Base.html#M000565">ActiveRecord::Base.connection_pool</a>.<a
href="ConnectionPool.html#M000356">with_connection</a>(&block), which
obtains a <a href="ConnectionPool.html#M000354">connection</a>, yields it
as the sole argument to the block, and returns it to the pool after the
block completes.
</li>
</ol>
<p>
Connections in the pool are actually <a
href="AbstractAdapter.html">AbstractAdapter</a> objects (or objects
compatible with <a href="AbstractAdapter.html">AbstractAdapter</a>‘s
interface).
</p>
<h2>Options</h2>
<p>
There are two <a
href="ConnectionPool.html#M000354">connection</a>-pooling-related options
that you can add to your database <a
href="ConnectionPool.html#M000354">connection</a> configuration:
</p>
<ul>
<li><tt>pool</tt>: number indicating size of <a
href="ConnectionPool.html#M000354">connection</a> pool (default 5)
</li>
<li><tt>wait_timeout</tt>: number of seconds to block and wait for a <a
href="ConnectionPool.html#M000354">connection</a> before giving up and
raising a timeout error (default 5 seconds).
</li>
</ul>
</div>
</div>
<div id="method-list">
<h3 class="section-bar">Methods</h3>
<div class="name-list">
<a href="#M000362">checkin</a>
<a href="#M000361">checkout</a>
<a href="#M000359">clear_reloadable_connections!</a>
<a href="#M000360">clear_stale_cached_connections!</a>
<a href="#M000357">connected?</a>
<a href="#M000354">connection</a>
<a href="#M000358">disconnect!</a>
<a href="#M000353">new</a>
<a href="#M000355">release_connection</a>
<a href="#M000356">with_connection</a>
</div>
</div>
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<h3 class="section-bar">Attributes</h3>
<div class="name-list">
<table>
<tr class="top-aligned-row context-row">
<td class="context-item-name">spec</td>
<td class="context-item-value"> [R] </td>
<td class="context-item-desc"></td>
</tr>
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</div>
<!-- if method_list -->
<div id="methods">
<h3 class="section-bar">Public Class methods</h3>
<div id="method-M000353" class="method-detail">
<a name="M000353"></a>
<div class="method-heading">
<a href="ConnectionPool.src/M000353.html" target="Code" class="method-signature"
onclick="popupCode('ConnectionPool.src/M000353.html');return false;">
<span class="method-name">new</span><span class="method-args">(spec)</span>
</a>
</div>
<div class="method-description">
<p>
Creates a <a href="ConnectionPool.html#M000353">new</a> <a
href="ConnectionPool.html">ConnectionPool</a> object. <tt>spec</tt> is a
ConnectionSpecification object which describes database <a
href="ConnectionPool.html#M000354">connection</a> information (e.g.
adapter, host name, username, password, etc), as well as the maximum size
for this <a href="ConnectionPool.html">ConnectionPool</a>.
</p>
<p>
The default <a href="ConnectionPool.html">ConnectionPool</a> maximum size
is 5.
</p>
</div>
</div>
<h3 class="section-bar">Public Instance methods</h3>
<div id="method-M000362" class="method-detail">
<a name="M000362"></a>
<div class="method-heading">
<a href="ConnectionPool.src/M000362.html" target="Code" class="method-signature"
onclick="popupCode('ConnectionPool.src/M000362.html');return false;">
<span class="method-name">checkin</span><span class="method-args">(conn)</span>
</a>
</div>
<div class="method-description">
<p>
Check-in a database <a href="ConnectionPool.html#M000354">connection</a>
back into the pool, indicating that you no longer need this <a
href="ConnectionPool.html#M000354">connection</a>.
</p>
<p>
<tt>conn</tt>: an <a href="AbstractAdapter.html">AbstractAdapter</a>
object, which was obtained by earlier by calling <tt><a
href="ConnectionPool.html#M000361">checkout</a></tt> on this pool.
</p>
</div>
</div>
<div id="method-M000361" class="method-detail">
<a name="M000361"></a>
<div class="method-heading">
<a href="ConnectionPool.src/M000361.html" target="Code" class="method-signature"
onclick="popupCode('ConnectionPool.src/M000361.html');return false;">
<span class="method-name">checkout</span><span class="method-args">()</span>
</a>
</div>
<div class="method-description">
<p>
Check-out a database <a href="ConnectionPool.html#M000354">connection</a>
from the pool, indicating that you want to use it. You should call <a
href="ConnectionPool.html#M000362">checkin</a> when you no longer need
this.
</p>
<p>
This is done by either returning an existing <a
href="ConnectionPool.html#M000354">connection</a>, or by creating a <a
href="ConnectionPool.html#M000353">new</a> <a
href="ConnectionPool.html#M000354">connection</a>. If the maximum number of
connections for this pool has already been reached, but the pool is empty
(i.e. they‘re all being used), then this method will wait until a
thread has checked in a <a
href="ConnectionPool.html#M000354">connection</a>. The wait time is bounded
however: if no <a href="ConnectionPool.html#M000354">connection</a> can be
checked out within the timeout specified for this pool, then a <a
href="../ConnectionTimeoutError.html">ConnectionTimeoutError</a> exception
will be raised.
</p>
<p>
Returns: an <a href="AbstractAdapter.html">AbstractAdapter</a> object.
</p>
<p>
Raises:
</p>
<ul>
<li><a href="../ConnectionTimeoutError.html">ConnectionTimeoutError</a>: no <a
href="ConnectionPool.html#M000354">connection</a> can be obtained from the
pool within the timeout period.
</li>
</ul>
</div>
</div>
<div id="method-M000359" class="method-detail">
<a name="M000359"></a>
<div class="method-heading">
<a href="ConnectionPool.src/M000359.html" target="Code" class="method-signature"
onclick="popupCode('ConnectionPool.src/M000359.html');return false;">
<span class="method-name">clear_reloadable_connections!</span><span class="method-args">()</span>
</a>
</div>
<div class="method-description">
<p>
Clears the cache which maps classes
</p>
</div>
</div>
<div id="method-M000360" class="method-detail">
<a name="M000360"></a>
<div class="method-heading">
<a href="ConnectionPool.src/M000360.html" target="Code" class="method-signature"
onclick="popupCode('ConnectionPool.src/M000360.html');return false;">
<span class="method-name">clear_stale_cached_connections!</span><span class="method-args">()</span>
</a>
</div>
<div class="method-description">
<p>
Return any checked-out connections back to the pool by threads that are no
longer alive.
</p>
</div>
</div>
<div id="method-M000357" class="method-detail">
<a name="M000357"></a>
<div class="method-heading">
<a href="ConnectionPool.src/M000357.html" target="Code" class="method-signature"
onclick="popupCode('ConnectionPool.src/M000357.html');return false;">
<span class="method-name">connected?</span><span class="method-args">()</span>
</a>
</div>
<div class="method-description">
<p>
Returns true if a <a href="ConnectionPool.html#M000354">connection</a> has
already been opened.
</p>
</div>
</div>
<div id="method-M000354" class="method-detail">
<a name="M000354"></a>
<div class="method-heading">
<a href="ConnectionPool.src/M000354.html" target="Code" class="method-signature"
onclick="popupCode('ConnectionPool.src/M000354.html');return false;">
<span class="method-name">connection</span><span class="method-args">()</span>
</a>
</div>
<div class="method-description">
<p>
Retrieve the <a href="ConnectionPool.html#M000354">connection</a>
associated with the current thread, or call <a
href="ConnectionPool.html#M000361">checkout</a> to obtain one if necessary.
</p>
<p>
<a href="ConnectionPool.html#M000354">connection</a> can be called any
number of times; the <a href="ConnectionPool.html#M000354">connection</a>
is held in a hash keyed by the thread id.
</p>
</div>
</div>
<div id="method-M000358" class="method-detail">
<a name="M000358"></a>
<div class="method-heading">
<a href="ConnectionPool.src/M000358.html" target="Code" class="method-signature"
onclick="popupCode('ConnectionPool.src/M000358.html');return false;">
<span class="method-name">disconnect!</span><span class="method-args">()</span>
</a>
</div>
<div class="method-description">
<p>
Disconnects all connections in the pool, and clears the pool.
</p>
</div>
</div>
<div id="method-M000355" class="method-detail">
<a name="M000355"></a>
<div class="method-heading">
<a href="ConnectionPool.src/M000355.html" target="Code" class="method-signature"
onclick="popupCode('ConnectionPool.src/M000355.html');return false;">
<span class="method-name">release_connection</span><span class="method-args">()</span>
</a>
</div>
<div class="method-description">
<p>
Signal that the thread is finished with the current <a
href="ConnectionPool.html#M000354">connection</a>. <a
href="ConnectionPool.html#M000355">release_connection</a> releases the <a
href="ConnectionPool.html#M000354">connection</a>-thread association and
returns the <a href="ConnectionPool.html#M000354">connection</a> to the
pool.
</p>
</div>
</div>
<div id="method-M000356" class="method-detail">
<a name="M000356"></a>
<div class="method-heading">
<a href="ConnectionPool.src/M000356.html" target="Code" class="method-signature"
onclick="popupCode('ConnectionPool.src/M000356.html');return false;">
<span class="method-name">with_connection</span><span class="method-args">() {|conn| ...}</span>
</a>
</div>
<div class="method-description">
<p>
Reserve a <a href="ConnectionPool.html#M000354">connection</a>, and yield
it to a block. Ensure the <a
href="ConnectionPool.html#M000354">connection</a> is checked back in when
finished.
</p>
</div>
</div>
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