class Sequel::ShardedTimedQueueConnectionPool

A connection pool allowing multi-threaded access to a sharded pool of connections, using a timed queue (only available in Ruby 3.2+).

Attributes

max_size[R]

The maximum number of connections this pool will create per shard.

Public Class Methods

new(db, opts = OPTS) click to toggle source

The following additional options are respected:

:max_connections

The maximum number of connections the connection pool will open (default 4)

:pool_timeout

The amount of seconds to wait to acquire a connection before raising a PoolTimeout (default 5)

: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.

Calls superclass method Sequel::ConnectionPool::new
   # File lib/sequel/connection_pool/sharded_timed_queue.rb
24 def initialize(db, opts = OPTS)
25   super
26 
27   @max_size = Integer(opts[:max_connections] || 4)
28   raise(Sequel::Error, ':max_connections must be positive') if @max_size < 1
29   @mutex = Mutex.new  
30   @timeout = Float(opts[:pool_timeout] || 5)
31 
32   @allocated = {}
33   @sizes = {}
34   @queues = {}
35   @servers = opts.fetch(:servers_hash, Hash.new(:default))
36 
37   add_servers([:default])
38   add_servers(opts[:servers].keys) if opts[:servers]
39 end

Public Instance Methods

add_servers(servers) click to toggle source

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_timed_queue.rb
43 def add_servers(servers)
44   sync do
45     servers.each do |server|
46       next if @servers.has_key?(server)
47 
48       @servers[server] = server
49       @sizes[server] = 0
50       @queues[server] = Queue.new
51       (@allocated[server] = {}).compare_by_identity
52     end
53   end
54   nil
55 end
all_connections() { |conn| ... } click to toggle source

Yield all of the available connections, and the one currently allocated to this thread (if one is allocated). This will not yield connections currently allocated to other threads, as it is not safe to operate on them.

   # File lib/sequel/connection_pool/sharded_timed_queue.rb
60 def all_connections
61   thread = Sequel.current
62   sync{@queues.to_a}.each do |server, queue|
63     if conn = owned_connection(thread, server)
64       yield conn
65     end
66 
67     # Use a hash to record all connections already seen.  As soon as we
68     # come across a connection we've already seen, we stop the loop.
69     conns = {}
70     conns.compare_by_identity
71     while true
72       conn = nil
73       begin
74         break unless (conn = queue.pop(timeout: 0)) && !conns[conn]
75         conns[conn] = true
76         yield conn
77       ensure
78         queue.push(conn) if conn
79       end
80     end
81   end
82 
83   nil
84 end
disconnect(opts=OPTS) click to toggle source

Removes all connections currently in the pool’s queue. This method has the effect of disconnecting from the database, assuming that no connections are currently being used.

Once a connection is requested using hold, the connection pool creates new connections to the database.

If the :server option is provided, it should be a symbol or array of symbols, and then the method will only disconnect connectsion from those specified shards.

    # File lib/sequel/connection_pool/sharded_timed_queue.rb
 95 def disconnect(opts=OPTS)
 96   (opts[:server] ? Array(opts[:server]) : sync{@servers.keys}).each do |server|
 97     raise Sequel::Error, "invalid server" unless queue = sync{@queues[server]}
 98     while conn = queue.pop(timeout: 0)
 99       disconnect_pool_connection(conn, server)
100     end
101     fill_queue(server)
102   end
103   nil
104 end
hold(server=:default) { |conn| ... } click to toggle source

Chooses the first available connection for 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_timed_queue.rb
119 def hold(server=:default)
120   server = pick_server(server)
121   t = Sequel.current
122   if conn = owned_connection(t, server)
123     return yield(conn)
124   end
125 
126   begin
127     conn = acquire(t, server)
128     yield conn
129   rescue Sequel::DatabaseDisconnectError, *@error_classes => e
130     if disconnect_error?(e)
131       oconn = conn
132       conn = nil
133       disconnect_pool_connection(oconn, server) if oconn
134       sync{@allocated[server].delete(t)}
135       fill_queue(server)
136     end
137     raise
138   ensure
139     release(t, conn, server) if conn
140   end
141 end
pool_type() click to toggle source
    # File lib/sequel/connection_pool/sharded_timed_queue.rb
190 def pool_type
191   :sharded_timed_queue
192 end
remove_servers(servers) click to toggle source

Remove servers from the connection pool. Similar to disconnecting from all given servers, except that after it is used, future requests for the servers will use the :default server instead.

Note that an error will be raised if there are any connections currently checked out for the given servers.

    # File lib/sequel/connection_pool/sharded_timed_queue.rb
154 def remove_servers(servers)
155   conns = []
156   raise(Sequel::Error, "cannot remove default server") if servers.include?(:default)
157 
158   sync do
159     servers.each do |server|
160       next unless @servers.has_key?(server)
161 
162       queue = @queues[server]
163 
164       while conn = queue.pop(timeout: 0)
165         @sizes[server] -= 1
166         conns << conn
167       end
168 
169       unless @sizes[server] == 0
170         raise Sequel::Error, "cannot remove server #{server} as it has allocated connections"
171       end
172 
173       @servers.delete(server)
174       @sizes.delete(server)
175       @queues.delete(server)
176       @allocated.delete(server)
177     end
178   end
179 
180   nil
181 ensure
182   disconnect_connections(conns)
183 end
servers() click to toggle source

Return an array of symbols for servers in the connection pool.

    # File lib/sequel/connection_pool/sharded_timed_queue.rb
186 def servers
187   sync{@servers.keys}
188 end
size(server=:default) click to toggle source

The total number of connections in the pool. Using a non-existant server will return nil.

    # File lib/sequel/connection_pool/sharded_timed_queue.rb
144 def size(server=:default)
145   sync{@sizes[server]}
146 end

Private Instance Methods

acquire(thread, server) click to toggle source

Assigns a connection to the supplied thread, if one is available.

This should return a connection if one is available within the timeout, or raise PoolTimeout if a connection could not be acquired within the timeout.

Calling code should not have the mutex when calling this.

    # File lib/sequel/connection_pool/sharded_timed_queue.rb
306 def acquire(thread, server)
307   queue = sync{@queues[server]}
308   if conn = queue.pop(timeout: 0) || try_make_new(server) || queue.pop(timeout: @timeout)
309     sync{@allocated[server][thread] = conn}
310   else
311     name = db.opts[:name]
312     raise ::Sequel::PoolTimeout, "timeout: #{@timeout}, server: #{server}#{", database name: #{name}" if name}"
313   end
314 end
can_make_new?(server, current_size) click to toggle source

Whether the given size is less than the maximum size of the pool. In that case, the pool’s current size is incremented. If this method returns true, space in the pool for the connection is preallocated, and preallocated_make_new should be called to create the connection.

Calling code should have the mutex when calling this.

    # File lib/sequel/connection_pool/sharded_timed_queue.rb
259 def can_make_new?(server, current_size)
260   if @max_size > current_size
261     @sizes[server] += 1
262   end
263 end
checkin_connection(conn, server) click to toggle source

Adds a connection to the queue of available connections, returns the connection.

    # File lib/sequel/connection_pool/sharded_timed_queue.rb
363 def checkin_connection(conn, server)
364   sync{@queues[server]}.push(conn)
365   conn
366 end
disconnect_connections(conns) click to toggle source

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_timed_queue.rb
218 def disconnect_connections(conns)
219   conns.each{|conn| disconnect_connection(conn)}
220 end
disconnect_pool_connection(conn, server) click to toggle source

Decrement the current size of the pool for the server when disconnecting connections.

Calling code should not have the mutex when calling this.

    # File lib/sequel/connection_pool/sharded_timed_queue.rb
225 def disconnect_pool_connection(conn, server)
226   sync{@sizes[server] -= 1}
227   disconnect_connection(conn)
228 end
fill_queue(server) click to toggle source

If there are any threads waiting on the queue, try to create new connections in a separate thread if the pool is not yet at the maximum size.

The reason for this method is to handle cases where acquire could not retrieve a connection immediately, and the pool was already at the maximum size. In that case, the acquire will wait on the queue until the timeout. This method is called after disconnecting to potentially add new connections to the pool, so the threads that are currently waiting for connections do not timeout after the pool is no longer full.

    # File lib/sequel/connection_pool/sharded_timed_queue.rb
241 def fill_queue(server)
242   queue = sync{@queues[server]}
243   if queue.num_waiting > 0
244     Thread.new do
245       while queue.num_waiting > 0 && (conn = try_make_new(server))
246         queue.push(conn)
247       end
248     end
249   end
250 end
owned_connection(thread, server) click to toggle source

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_timed_queue.rb
318 def owned_connection(thread, server)
319   sync{@allocated[server][thread]}
320 end
pick_server(server) click to toggle source

If the server given is in the hash, return it, otherwise, return the default server.

    # File lib/sequel/connection_pool/sharded_timed_queue.rb
323 def pick_server(server)
324   sync{@servers[server]}
325 end
preallocated_make_new(server) click to toggle source

Create a new connection, after the pool’s current size has already been updated to account for the new connection. If there is an exception when creating the connection, decrement the current size.

This should only be called after can_make_new?. If there is an exception between when can_make_new? is called and when preallocated_make_new is called, it has the effect of reducing the maximum size of the connection pool by 1, since the current size of the pool will show a higher number than the number of connections allocated or in the queue.

Calling code should not have the mutex when calling this.

    # File lib/sequel/connection_pool/sharded_timed_queue.rb
208 def preallocated_make_new(server)
209   make_new(server)
210 rescue Exception
211   sync{@sizes[server] -= 1}
212   raise
213 end
preconnect(concurrent = false) click to toggle source

Create the maximum number of connections immediately. This should not be called with a true argument unless no code is currently operating on the database.

Calling code should not have the mutex when calling this.

    # File lib/sequel/connection_pool/sharded_timed_queue.rb
331 def preconnect(concurrent = false)
332   conn_servers = sync{@servers.keys}.map!{|s| Array.new(@max_size - @sizes[s], s)}.flatten!
333 
334   if concurrent
335     conn_servers.map! do |server|
336       queue = sync{@queues[server]}
337       Thread.new do 
338         if conn = try_make_new(server)
339           queue.push(conn)
340         end
341       end
342     end.each(&:value)
343   else
344     conn_servers.each do |server|
345       if conn = try_make_new(server)
346         sync{@queues[server]}.push(conn)
347       end
348     end
349   end
350 
351   nil
352 end
release(thread, _, server) click to toggle source

Releases the connection assigned to the supplied thread back to the pool.

Calling code should not have the mutex when calling this.

    # File lib/sequel/connection_pool/sharded_timed_queue.rb
357 def release(thread, _, server)
358   checkin_connection(sync{@allocated[server].delete(thread)}, server)
359   nil
360 end
sync() { || ... } click to toggle source

Yield to the block while inside the mutex.

Calling code should not have the mutex when calling this.

    # File lib/sequel/connection_pool/sharded_timed_queue.rb
371 def sync
372   @mutex.synchronize{yield}
373 end
try_make_new(server) click to toggle source

Try to make a new connection if there is space in the pool. If the pool is already full, look for dead threads/fibers and disconnect the related connections.

Calling code should not have the mutex when calling this.

    # File lib/sequel/connection_pool/sharded_timed_queue.rb
270 def try_make_new(server)
271   return preallocated_make_new(server) if sync{can_make_new?(server, @sizes[server])}
272 
273   to_disconnect = nil
274   do_make_new = false
275 
276   sync do
277     current_size = @sizes[server]
278     alloc = @allocated[server]
279     alloc.keys.each do |t|
280       unless t.alive?
281         (to_disconnect ||= []) << alloc.delete(t)
282         current_size -= 1
283       end
284     end
285   
286     do_make_new = true if can_make_new?(server, current_size)
287   end
288 
289   begin
290     preallocated_make_new(server) if do_make_new
291   ensure
292     if to_disconnect
293       to_disconnect.each{|conn| disconnect_pool_connection(conn, server)}
294       fill_queue(server)
295     end
296   end
297 end