From 65e2bb02346cc7e36a350af31aa9ed24b472ef39 Mon Sep 17 00:00:00 2001
From: spiral <spiral@spiral.sh>
Date: Tue, 14 Jun 2022 23:11:55 -0400
Subject: [PATCH] feat(bot): remove cluster-local DM channel cache

---
 PluralKit.Bot/BotMetrics.cs                   |  7 -----
 .../Services/PrivateChannelService.cs         | 30 ++++++-------------
 2 files changed, 9 insertions(+), 28 deletions(-)

diff --git a/PluralKit.Bot/BotMetrics.cs b/PluralKit.Bot/BotMetrics.cs
index 94dd0f6e..23eb324e 100644
--- a/PluralKit.Bot/BotMetrics.cs
+++ b/PluralKit.Bot/BotMetrics.cs
@@ -22,13 +22,6 @@ public static class BotMetrics
         Context = "Bot"
     };
 
-    public static MeterOptions LocalDMCacheHits => new()
-    {
-        Name = "Cluster local DM Cache Hits",
-        MeasurementUnit = Unit.Calls,
-        Context = "Bot"
-    };
-
     public static MeterOptions DatabaseDMCacheHits => new()
     {
         Name = "Database DM Cache Hits",
diff --git a/PluralKit.Bot/Services/PrivateChannelService.cs b/PluralKit.Bot/Services/PrivateChannelService.cs
index 3c2781e7..dc1ea03a 100644
--- a/PluralKit.Bot/Services/PrivateChannelService.cs
+++ b/PluralKit.Bot/Services/PrivateChannelService.cs
@@ -11,8 +11,6 @@ namespace PluralKit.Bot;
 
 public class PrivateChannelService
 {
-    private static readonly Dictionary<ulong, ulong> _channelsCache = new();
-
     private readonly IMetrics _metrics;
     private readonly ILogger _logger;
     private readonly ModelRepository _repo;
@@ -27,42 +25,32 @@ public class PrivateChannelService
 
     public async Task TrySavePrivateChannel(MessageCreateEvent evt)
     {
-        if (evt.GuildId != null) return;
-        if (_channelsCache.TryGetValue(evt.Author.Id, out _)) return;
-
-        await SaveDmChannel(evt.Author.Id, evt.ChannelId);
+        if (evt.GuildId == null) await SaveDmChannel(evt.Author.Id, evt.ChannelId);
     }
 
     public async Task<ulong> GetOrCreateDmChannel(ulong userId)
     {
-        if (_channelsCache.TryGetValue(userId, out var cachedChannelId))
-        {
-            _metrics.Measure.Meter.Mark(BotMetrics.LocalDMCacheHits);
-            return cachedChannelId;
-        }
-
         var channelId = await _repo.GetDmChannel(userId);
-        if (channelId == null)
+        if (channelId != null)
         {
-            _metrics.Measure.Meter.Mark(BotMetrics.DMCacheMisses);
-            var channel = await _rest.CreateDm(userId);
-            channelId = channel.Id;
+            _metrics.Measure.Meter.Mark(BotMetrics.DatabaseDMCacheHits);
+            return channelId.Value;
         }
 
-        _metrics.Measure.Meter.Mark(BotMetrics.DatabaseDMCacheHits);
+        _metrics.Measure.Meter.Mark(BotMetrics.DMCacheMisses);
+
+        var channel = await _rest.CreateDm(userId);
 
         // spawn off saving the channel as to not block the current thread
-        // todo: don't save to database again if we just fetched it from there
-        _ = SaveDmChannel(userId, channelId.Value);
+        _ = SaveDmChannel(userId, channel.Id);
 
-        return channelId.Value;
+        return channel.Id;
     }
 
     private async Task SaveDmChannel(ulong userId, ulong channelId)
     {
         try
         {
-            _channelsCache.Add(userId, channelId);
             await _repo.UpdateAccount(userId, new() { DmChannel = channelId });
         }
         catch (Exception e)