Fix database connection pool contention (maybe)

Instead of acquiring a connection per service per request, we
acquire connections more often but at a more granular level, meaning
they're also disposed of more quickly instead of staying for a long time
in case of long-running commands or leaks.

PluralKit.Bot/Bot.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Data;
+using System.Data.Common;
 using System.Diagnostics;
 using System.IO;
 using System.Linq;
@@ -32,8 +33,8 @@ namespace PluralKit.Bot
             using (var services = BuildServiceProvider())
             {
                 Console.WriteLine("- Connecting to database...");
-                var connection = services.GetRequiredService<IDbConnection>() as NpgsqlConnection;
-                await Schema.CreateTables(connection);
+                using (var conn = services.GetRequiredService<DbConnectionFactory>().Obtain())
+                    await Schema.CreateTables(conn);
 
                 Console.WriteLine("- Connecting to Discord...");
                 var client = services.GetRequiredService<IDiscordClient>() as DiscordSocketClient;
@@ -51,13 +52,7 @@ namespace PluralKit.Bot
                 .AddTransient(_ => _config.GetSection("PluralKit").Get<CoreConfig>() ?? new CoreConfig())
                 .AddTransient(_ => _config.GetSection("PluralKit").GetSection("Bot").Get<BotConfig>() ?? new BotConfig())
                 
-                .AddTransient<IDbConnection>(svc =>
-                {
-                    
-                    var conn = new NpgsqlConnection(svc.GetRequiredService<CoreConfig>().Database);
-                    conn.Open();
-                    return conn;
-                })
+                .AddTransient(svc => new DbConnectionFactory(svc.GetRequiredService<CoreConfig>().Database))
                 
                 .AddSingleton<IDiscordClient, DiscordSocketClient>()
                 .AddSingleton<Bot>()
@@ -170,9 +165,10 @@ namespace PluralKit.Bot
                 // If it does, fetch the sender's system (because most commands need that) into the context,
                 // and start command execution
                 // Note system may be null if user has no system, hence `OrDefault`
-                var connection = serviceScope.ServiceProvider.GetService<IDbConnection>();
-                var system = await connection.QueryFirstOrDefaultAsync<PKSystem>("select systems.* from systems, accounts where accounts.uid = @Id and systems.id = accounts.system", new { Id = arg.Author.Id });
-                await _commands.ExecuteAsync(new PKCommandContext(_client, arg, connection, system), argPos, serviceScope.ServiceProvider);
+                PKSystem system;
+                using (var conn = serviceScope.ServiceProvider.GetService<DbConnectionFactory>().Obtain())
+                    system = await conn.QueryFirstOrDefaultAsync<PKSystem>("select systems.* from systems, accounts where accounts.uid = @Id and systems.id = accounts.system", new { Id = arg.Author.Id });
+                await _commands.ExecuteAsync(new PKCommandContext(_client, arg, system), argPos, serviceScope.ServiceProvider);
             }
             else
             {

PluralKit.Bot/Services/LogChannelService.cs

@@ -11,13 +11,13 @@ namespace PluralKit.Bot {
 
     public class LogChannelService {
         private IDiscordClient _client;
-        private IDbConnection _connection;
+        private DbConnectionFactory _conn;
         private EmbedService _embed;
 
-        public LogChannelService(IDiscordClient client, IDbConnection connection, EmbedService embed)
+        public LogChannelService(IDiscordClient client, DbConnectionFactory conn, EmbedService embed)
         {
             this._client = client;
-            this._connection = connection;
+            this._conn = conn;
             this._embed = embed;
         }
 
@@ -30,9 +30,14 @@ namespace PluralKit.Bot {
         }
 
         public async Task<ITextChannel> GetLogChannel(IGuild guild) {
-            var server = await _connection.QueryFirstOrDefaultAsync<ServerDefinition>("select * from servers where id = @Id", new { Id = guild.Id });
-            if (server?.LogChannel == null) return null;
-            return await _client.GetChannelAsync(server.LogChannel.Value) as ITextChannel;
+            using (var conn = _conn.Obtain())
+            {
+                var server =
+                    await conn.QueryFirstOrDefaultAsync<ServerDefinition>("select * from servers where id = @Id",
+                        new {Id = guild.Id});
+                if (server?.LogChannel == null) return null;
+                return await _client.GetChannelAsync(server.LogChannel.Value) as ITextChannel;
+            }
         }
 
         public async Task SetLogChannel(IGuild guild, ITextChannel newLogChannel) {
@@ -41,7 +46,12 @@ namespace PluralKit.Bot {
                 LogChannel = newLogChannel?.Id
             };
 
-            await _connection.QueryAsync("insert into servers (id, log_channel) values (@Id, @LogChannel) on conflict (id) do update set log_channel = @LogChannel", def);
+            using (var conn = _conn.Obtain())
+            {
+                await conn.QueryAsync(
+                    "insert into servers (id, log_channel) values (@Id, @LogChannel) on conflict (id) do update set log_channel = @LogChannel",
+                    def);
+            }
         }
     }
 }

PluralKit.Bot/Services/ProxyService.cs

@@ -28,17 +28,17 @@ namespace PluralKit.Bot
 
     class ProxyService {
         private IDiscordClient _client;
-        private IDbConnection _connection;
+        private DbConnectionFactory _conn;
         private LogChannelService _logger;
         private WebhookCacheService _webhookCache;
         private MessageStore _messageStorage;
         private EmbedService _embeds;
         
-        public ProxyService(IDiscordClient client, WebhookCacheService webhookCache, IDbConnection connection, LogChannelService logger, MessageStore messageStorage, EmbedService embeds)
+        public ProxyService(IDiscordClient client, WebhookCacheService webhookCache, DbConnectionFactory conn, LogChannelService logger, MessageStore messageStorage, EmbedService embeds)
         {
             _client = client;
             _webhookCache = webhookCache;
-            _connection = connection;
+            _conn = conn;
             _logger = logger;
             _messageStorage = messageStorage;
             _embeds = embeds;
@@ -76,11 +76,16 @@ namespace PluralKit.Bot
             return null;
         }
 
-        public async Task HandleMessageAsync(IMessage message) {
-            var results = await _connection.QueryAsync<PKMember, PKSystem, ProxyDatabaseResult>(
-                "select members.*, systems.* from members, systems, accounts where members.system = systems.id and accounts.system = systems.id and accounts.uid = @Uid", 
-                (member, system) =>
-                    new ProxyDatabaseResult { Member = member, System = system }, new { Uid = message.Author.Id });
+        public async Task HandleMessageAsync(IMessage message)
+        {
+            IEnumerable<ProxyDatabaseResult> results;
+            using (var conn = _conn.Obtain())
+            {
+                results = await conn.QueryAsync<PKMember, PKSystem, ProxyDatabaseResult>(
+                    "select members.*, systems.* from members, systems, accounts where members.system = systems.id and accounts.system = systems.id and accounts.uid = @Uid",
+                    (member, system) =>
+                        new ProxyDatabaseResult {Member = member, System = system}, new {Uid = message.Author.Id});
+            }
 
             // Find a member with proxy tags matching the message
             var match = GetProxyTagMatch(message.Content, results);

PluralKit.Bot/Utils.cs

@@ -152,14 +152,12 @@ namespace PluralKit.Bot
     /// Subclass of ICommandContext with PK-specific additional fields and functionality
     public class PKCommandContext : SocketCommandContext
     {
-        public IDbConnection Connection { get; }
         public PKSystem SenderSystem { get; }
         
         private object _entity;
 
-        public PKCommandContext(DiscordSocketClient client, SocketUserMessage msg, IDbConnection connection, PKSystem system) : base(client, msg)
+        public PKCommandContext(DiscordSocketClient client, SocketUserMessage msg, PKSystem system) : base(client, msg)
         {
-            Connection = connection;
             SenderSystem = system;
         }