class Sequel::ShardedThreadedConnectionPool
The slowest and most advanced connection pool, dealing with both multi-threaded access and configurations with multiple shards/servers.
In addition, this pool subclass also handles scheduling in-use connections to be removed from the pool when they are returned to it.
Public Class Methods
The following additional options are respected:
- :servers
-
A hash of servers to use. Keys should be symbols. If not present, will use a single :default server.
- :servers_hash
-
The base hash to use for the servers. By default, Sequel uses Hash.new(:default). You can use a hash with a default proc that raises an error if you want to catch all cases where a nonexistent server is used.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 17 def initialize(db, opts = OPTS) super @available_connections = {} @connections_to_remove = [] @connections_to_disconnect = [] @servers = opts.fetch(:servers_hash, Hash.new(:default)) remove_instance_variable(:@waiter) remove_instance_variable(:@allocated) @allocated = {} @waiters = {} add_servers([:default]) add_servers(opts[:servers].keys) if opts[:servers] end
Public Instance Methods
Adds new servers to the connection pool. Allows for dynamic expansion of
the potential replicas/shards at runtime. servers
argument
should be an array of symbols.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 34 def add_servers(servers) sync do servers.each do |server| unless @servers.has_key?(server) @servers[server] = server @available_connections[server] = [] allocated = {} allocated.compare_by_identity @allocated[server] = allocated @waiters[server] = ConditionVariable.new end end end end
Yield all of the available connections, and the ones currently allocated to this thread. This will not yield connections currently allocated to other threads, as it is not safe to operate on them. This holds the mutex while it is yielding all of the connections, which means that until the method's block returns, the pool is locked.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 62 def all_connections t = Sequel.current sync do @allocated.values.each do |threads| threads.each do |thread, conn| yield conn if t == thread end end @available_connections.values.each{|v| v.each{|c| yield c}} end end
A hash of connections currently being used for the given server, key is the Thread, value is the connection. Nonexistent servers will return nil. Treat this as read only, do not modify the resulting object. The calling code should already have the mutex before calling this.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 53 def allocated(server=:default) @allocated[server] end
An array of connections opened but not currently used, for the given server. Nonexistent servers will return nil. Treat this as read only, do not modify the resulting object. The calling code should already have the mutex before calling this.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 78 def available_connections(server=:default) @available_connections[server] end
Removes all connections currently available on all servers, optionally yielding each connection to the given block. This method has the effect of disconnecting from the database, assuming that no connections are currently being used. If connections are being used, they are scheduled to be disconnected as soon as they are returned to the pool.
Once a connection is requested using hold, the connection pool creates new connections to the database. Options:
- :server
-
Should be a symbol specifing the server to disconnect from, or an array of symbols to specify multiple servers.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 99 def disconnect(opts=OPTS) (opts[:server] ? Array(opts[:server]) : sync{@servers.keys}).each do |s| disconnect_connections(sync{disconnect_server_connections(s)}) end end
# File lib/sequel/connection_pool/sharded_threaded.rb, line 105 def freeze @servers.freeze super end
Chooses the first available connection to the given server, or if none are available, creates a new connection. Passes the connection to the supplied block:
pool.hold(:server1) {|conn| conn.execute('DROP TABLE posts')}
Pool#hold is re-entrant, meaning it can be called recursively in the same thread without blocking.
If no connection is immediately available and the pool is already using the maximum number of connections, Pool#hold will block until a connection is available or the timeout expires. If the timeout expires before a connection can be acquired, a Sequel::PoolTimeout is raised.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 123 def hold(server=:default) server = pick_server(server) t = Sequel.current if conn = owned_connection(t, server) return yield(conn) end begin conn = acquire(t, server) yield conn rescue Sequel::DatabaseDisconnectError, *@error_classes => e sync{@connections_to_remove << conn} if conn && disconnect_error?(e) raise ensure sync{release(t, conn, server)} if conn while dconn = sync{@connections_to_disconnect.shift} disconnect_connection(dconn) end end end
# File lib/sequel/connection_pool/sharded_threaded.rb, line 172 def pool_type :sharded_threaded end
Remove servers from the connection pool. Similar to disconnecting from all given servers, except that after it is used, future requests for the server will use the :default server instead.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 146 def remove_servers(servers) conns = [] raise(Sequel::Error, "cannot remove default server") if servers.include?(:default) sync do servers.each do |server| if @servers.include?(server) conns.concat(disconnect_server_connections(server)) @waiters.delete(server) @available_connections.delete(server) @allocated.delete(server) @servers.delete(server) end end end nil ensure disconnect_connections(conns) end
Return an array of symbols for servers in the connection pool.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 168 def servers sync{@servers.keys} end
The total number of connections opened for the given server. Nonexistent servers will return the created count of the default server. The calling code should NOT have the mutex before calling this.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 85 def size(server=:default) @mutex.synchronize{_size(server)} end
Private Instance Methods
The total number of connections opened for the given server. The calling code should already have the mutex before calling this.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 180 def _size(server) server = @servers[server] @allocated[server].length + @available_connections[server].length end
Assigns a connection to the supplied thread, if one is available. The calling code should NOT already have the mutex when calling this.
This should return a connection if one is available within the timeout, or nil if a connection could not be acquired within the timeout.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 191 def acquire(thread, server) if conn = assign_connection(thread, server) return conn end timeout = @timeout timer = Sequel.start_timer sync do @waiters[server].wait(@mutex, timeout) if conn = next_available(server) return(allocated(server)[thread] = conn) end end until conn = assign_connection(thread, server) elapsed = Sequel.elapsed_seconds_since(timer) # :nocov: raise_pool_timeout(elapsed, server) if elapsed > timeout # It's difficult to get to this point, it can only happen if there is a race condition # where a connection cannot be acquired even after the thread is signalled by the condition variable sync do @waiters[server].wait(@mutex, timeout - elapsed) if conn = next_available(server) return(allocated(server)[thread] = conn) end end # :nocov: end conn end
Assign a connection to the thread, or return nil if one cannot be assigned. The caller should NOT have the mutex before calling this.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 227 def assign_connection(thread, server) alloc = nil do_make_new = false sync do alloc = allocated(server) if conn = next_available(server) alloc[thread] = conn return conn end if (n = _size(server)) >= (max = @max_size) alloc.to_a.each do |t,c| unless t.alive? remove(t, c, server) end end n = nil end if (n || _size(server)) < max do_make_new = alloc[thread] = true end end # Connect to the database outside of the connection pool mutex, # as that can take a long time and the connection pool mutex # shouldn't be locked while the connection takes place. if do_make_new begin conn = make_new(server) sync{alloc[thread] = conn} ensure unless conn sync{alloc.delete(thread)} end end end conn end
Return a connection to the pool of available connections for the server, returns the connection. The calling code should already have the mutex before calling this.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 272 def checkin_connection(server, conn) available_connections(server) << conn @waiters[server].signal conn end
Disconnect all available connections immediately, and schedule currently allocated connections for disconnection as soon as they are returned to the pool. The calling code should NOT have the mutex before calling this.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 298 def disconnect_connections(conns) conns.each{|conn| disconnect_connection(conn)} end
Clear the array of available connections for the server, returning an array of previous available connections that should be disconnected (or nil if none should be). Mark any allocated connections to be removed when they are checked back in. The calling code should already have the mutex before calling this.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 282 def disconnect_server_connections(server) remove_conns = allocated(server) dis_conns = available_connections(server) raise Sequel::Error, "invalid server: #{server}" unless remove_conns && dis_conns @connections_to_remove.concat(remove_conns.values) conns = dis_conns.dup dis_conns.clear @waiters[server].signal conns end
Return the next available connection in the pool for the given server, or nil if there is not currently an available connection for the server. The calling code should already have the mutex before calling this.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 305 def next_available(server) case @connection_handling when :stack available_connections(server).pop else available_connections(server).shift end end
Returns the connection owned by the supplied thread for the given server, if any. The calling code should NOT already have the mutex before calling this.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 316 def owned_connection(thread, server) sync{@allocated[server][thread]} end
If the server given is in the hash, return it, otherwise, return the default server.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 321 def pick_server(server) sync{@servers[server]} end
Create the maximum number of connections immediately. The calling code should NOT have the mutex before calling this.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 327 def preconnect(concurrent = false) conn_servers = sync{@servers.keys}.map!{|s| Array.new(max_size - _size(s), s)}.flatten! if concurrent conn_servers.map!{|s| Thread.new{[s, make_new(s)]}}.map!(&:value) else conn_servers.map!{|s| [s, make_new(s)]} end sync{conn_servers.each{|s, conn| checkin_connection(s, conn)}} end
Raise a PoolTimeout error showing the current timeout, the elapsed time, the server the connection attempt was made to, and the database's name (if any).
# File lib/sequel/connection_pool/sharded_threaded.rb, line 341 def raise_pool_timeout(elapsed, server) name = db.opts[:name] raise ::Sequel::PoolTimeout, "timeout: #{@timeout}, elapsed: #{elapsed}, server: #{server}#{", database name: #{name}" if name}" end
Releases the connection assigned to the supplied thread and server. If the server or connection given is scheduled for disconnection, remove the connection instead of releasing it back to the pool. The calling code should already have the mutex before calling this.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 350 def release(thread, conn, server) if @connections_to_remove.include?(conn) remove(thread, conn, server) else conn = allocated(server).delete(thread) if @connection_handling == :disconnect @connections_to_disconnect << conn else checkin_connection(server, conn) end end if waiter = @waiters[server] waiter.signal end end
Removes the currently allocated connection from the connection pool. The calling code should already have the mutex before calling this.
# File lib/sequel/connection_pool/sharded_threaded.rb, line 370 def remove(thread, conn, server) @connections_to_remove.delete(conn) allocated(server).delete(thread) if @servers.include?(server) @connections_to_disconnect << conn end