Class: Pools::ConnectionPool
- Inherits:
-
Object
- Object
- Pools::ConnectionPool
- Includes:
- MonitorMixin
- Defined in:
- lib/pools/connection_pool.rb
Overview
Connection pool base class for managing Active Record database connections.
Introduction
A connection pool synchronizes thread access to a limited number of database connections. The basic idea is that each thread checks out a database connection from the pool, uses that connection, and checks the connection back in. ConnectionPool is completely thread-safe, and will ensure that a connection cannot be used by two threads at the same time, as long as ConnectionPool’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 checkout a connection anyway, then ConnectionPool will wait until some other thread has checked in a connection.
Obtaining (checking out) a connection
Connections can be obtained and used from a connection pool in several ways:
-
Simply use ActiveRecord::Base.connection as with Active Record 2.1 and earlier (pre-connection-pooling). Eventually, when you’re done with the connection(s) and wish it to be returned to the pool, you call ActiveRecord::Base.clear_active_connections!. This will be the default behavior for Active Record when used in conjunction with Action Pack’s request handling cycle.
-
Manually check out a connection from the pool with ActiveRecord::Base.connection_pool.checkout. You are responsible for returning this connection to the pool when finished by calling ActiveRecord::Base.connection_pool.checkin(connection).
-
Use ActiveRecord::Base.connection_pool.with_connection(&block), which obtains a connection, yields it as the sole argument to the block, and returns it to the pool after the block completes.
Connections in the pool are actually AbstractAdapter objects (or objects compatible with AbstractAdapter’s interface).
Options
There are two connection-pooling-related options that you can add to your database connection configuration:
-
pool
: number indicating size of connection pool (default 5) -
wait_timeout
: number of seconds to block and wait for a connection before giving up and raising a timeout error (default 5 seconds).
Instance Attribute Summary collapse
-
#connections ⇒ Object
readonly
Returns the value of attribute connections.
-
#options ⇒ Object
readonly
Returns the value of attribute options.
Instance Method Summary collapse
-
#checkin(conn) ⇒ Object
Check-in a database connection back into the pool, indicating that you no longer need this connection.
-
#checkout ⇒ Object
Check-out a database connection from the pool, indicating that you want to use it.
-
#clear_stale_cached_connections! ⇒ Object
Return any checked-out connections back to the pool by threads that are no longer alive.
-
#connected? ⇒ Boolean
Returns true if a connection has already been opened.
-
#connection ⇒ Object
Retrieve the connection associated with the current thread, or call #checkout to obtain one if necessary.
-
#disconnect! ⇒ Object
Disconnects all connections in the pool, and clears the pool.
-
#initialize(pooled, options) ⇒ ConnectionPool
constructor
Creates a new ConnectionPool object.
-
#release_connection(with_id = current_connection_id) ⇒ Object
Signal that the thread is finished with the current connection.
-
#verify_active_connections! ⇒ Object
Verify active connections and remove and disconnect connections associated with stale threads.
-
#with_connection ⇒ Object
If a connection already exists yield it to the block.
Constructor Details
#initialize(pooled, options) ⇒ ConnectionPool
Creates a new ConnectionPool object. spec
is a ConnectionSpecification object which describes database connection information (e.g. adapter, host name, username, password, etc), as well as the maximum size for this ConnectionPool.
The default ConnectionPool maximum size is 5.
71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 |
# File 'lib/pools/connection_pool.rb', line 71 def initialize(pooled, ) super() @pooled = pooled @options = # The cache of reserved connections mapped to threads @reserved_connections = {} # The mutex used to synchronize pool access @queue = self.new_cond # default 5 second timeout unless on ruby 1.9 @timeout = [:wait_timeout] || 5 # default max pool size to 5 @size = ([:pool] && [:pool].to_i) || 5 @connections = [] @checked_out = [] end |
Instance Attribute Details
#connections ⇒ Object (readonly)
Returns the value of attribute connections.
63 64 65 |
# File 'lib/pools/connection_pool.rb', line 63 def connections @connections end |
#options ⇒ Object (readonly)
Returns the value of attribute options.
63 64 65 |
# File 'lib/pools/connection_pool.rb', line 63 def @options end |
Instance Method Details
#checkin(conn) ⇒ Object
Check-in a database connection back into the pool, indicating that you no longer need this connection.
conn
: an AbstractAdapter object, which was obtained by earlier by calling checkout
on this pool.
213 214 215 216 217 218 |
# File 'lib/pools/connection_pool.rb', line 213 def checkin(conn) synchronize do @checked_out.delete conn @queue.signal end end |
#checkout ⇒ Object
Check-out a database connection from the pool, indicating that you want to use it. You should call #checkin when you no longer need this.
This is done by either returning an existing connection, or by creating a new connection. 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 connection. The wait time is bounded however: if no connection can be checked out within the timeout specified for this pool, then a ConnectionTimeoutError exception will be raised.
Returns: an AbstractAdapter object.
Raises:
-
ConnectionTimeoutError: no connection can be obtained from the pool within the timeout period.
182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 |
# File 'lib/pools/connection_pool.rb', line 182 def checkout # Checkout an available connection synchronize do loop do conn = if @checked_out.size < @connections.size checkout_existing_connection elsif @connections.size < @size checkout_new_connection end return conn if conn @queue.wait(@timeout) if(@checked_out.size < @connections.size) next else clear_stale_cached_connections! if @size == @checked_out.size raise ConnectionTimeoutError, "could not obtain a pooled connection#{" within #{@timeout} seconds" if @timeout}. The max pool size is currently #{@size}; consider increasing it." end end end end end |
#clear_stale_cached_connections! ⇒ Object
Return any checked-out connections back to the pool by threads that are no longer alive.
154 155 156 157 158 159 160 161 162 163 164 |
# File 'lib/pools/connection_pool.rb', line 154 def clear_stale_cached_connections! synchronize do keys = @reserved_connections.keys - Thread.list.find_all { |t| t.alive? }.map { |thread| thread.object_id } keys.each do |key| checkin @reserved_connections[key] @reserved_connections.delete(key) end end end |
#connected? ⇒ Boolean
Returns true if a connection has already been opened.
125 126 127 |
# File 'lib/pools/connection_pool.rb', line 125 def connected? synchronize { !@connections.empty? } end |
#connection ⇒ Object
Retrieve the connection associated with the current thread, or call #checkout to obtain one if necessary.
#connection can be called any number of times; the connection is held in a hash keyed by the thread id.
97 98 99 100 101 |
# File 'lib/pools/connection_pool.rb', line 97 def connection @reserved_connections[current_connection_id] || synchronize do @reserved_connections[current_connection_id] ||= checkout end end |
#disconnect! ⇒ Object
Disconnects all connections in the pool, and clears the pool.
130 131 132 133 134 135 136 137 138 139 |
# File 'lib/pools/connection_pool.rb', line 130 def disconnect! synchronize do @reserved_connections = {} @connections.each do |conn| checkin conn @pooled.__disconnect(conn) end @connections = [] end end |
#release_connection(with_id = current_connection_id) ⇒ Object
Signal that the thread is finished with the current connection. #release_connection releases the connection-thread association and returns the connection to the pool.
106 107 108 109 110 111 |
# File 'lib/pools/connection_pool.rb', line 106 def release_connection(with_id = current_connection_id) synchronize do conn = @reserved_connections.delete(with_id) checkin conn if conn end end |
#verify_active_connections! ⇒ Object
Verify active connections and remove and disconnect connections associated with stale threads.
143 144 145 146 147 148 149 150 |
# File 'lib/pools/connection_pool.rb', line 143 def verify_active_connections! #:nodoc: synchronize do clear_stale_cached_connections! @connections.each do |connection| @pooled.__disconnect(connection) end end end |
#with_connection ⇒ Object
If a connection already exists yield it to the block. If no connection exists checkout a connection, yield it to the block, and checkin the connection when finished.
116 117 118 119 120 121 122 |
# File 'lib/pools/connection_pool.rb', line 116 def with_connection connection_id = current_connection_id fresh_connection = synchronize { !@reserved_connections[connection_id] } yield connection ensure release_connection(connection_id) if fresh_connection end |