From 2fd155e31da91ecbe2d3f3f8475eee485805cd41 Mon Sep 17 00:00:00 2001
From: Nil <22560738+NilPuig@users.noreply.github.com>
Date: Sat, 7 Feb 2026 15:13:58 +0800
Subject: [PATCH] Fix nil guard for MEMORY USAGE in memoryUsageCmd Lua script

MEMORY USAGE returns nil for keys that no longer exist (e.g., expired
or deleted task keys). In Lua, nil is converted to false (a boolean).
The script then attempts arithmetic on this boolean value, causing:

  ERR user_script:30: attempt to perform arithmetic on local 'bytes'
  (a boolean value)

This breaks the /api/queues endpoint in asynqmon, showing "Could not
retrieve queues live data" in the UI.

The fix adds nil guards around all three MEMORY USAGE calls on task
keys, and a divide-by-zero guard on agg_task_sample_size.

Tested in production with Redis 7.2 and asynq v0.25.1 worker.

Fixes #728
Related to #901
---
 internal/rdb/inspect.go | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/internal/rdb/inspect.go b/internal/rdb/inspect.go
index 4bd7975..8a8be62 100644
--- a/internal/rdb/inspect.go
+++ b/internal/rdb/inspect.go
@@ -264,7 +264,9 @@ for i=1,2 do
     if (table.getn(ids) > 0) then
         for _, id in ipairs(ids) do
             local bytes = redis.call("MEMORY", "USAGE", ARGV[1] .. id)
-            sample_total = sample_total + bytes
+            if bytes then
+                sample_total = sample_total + bytes
+            end
         end
         local n = redis.call("LLEN", KEYS[i])
         local avg = sample_total / table.getn(ids)
@@ -281,7 +283,9 @@ for i=3,6 do
     if (table.getn(ids) > 0) then
         for _, id in ipairs(ids) do
             local bytes = redis.call("MEMORY", "USAGE", ARGV[1] .. id)
-            sample_total = sample_total + bytes
+            if bytes then
+                sample_total = sample_total + bytes
+            end
         end
         local n = redis.call("ZCARD", KEYS[i])
         local avg = sample_total / table.getn(ids)
@@ -304,13 +308,17 @@ if table.getn(groups) > 0 then
 			local ids = redis.call("ZRANGE", group_key, 0, sample_size - 1)
 			for _, id in ipairs(ids) do
 				local bytes = redis.call("MEMORY", "USAGE", ARGV[1] .. id)
-				agg_task_sample_total = agg_task_sample_total + bytes
-				agg_task_sample_size = agg_task_sample_size + 1
+				if bytes then
+					agg_task_sample_total = agg_task_sample_total + bytes
+					agg_task_sample_size = agg_task_sample_size + 1
+				end
 			end
 		end
 	end
-	local avg = agg_task_sample_total / agg_task_sample_size
-	memusg = memusg + (avg * agg_task_count)
+	if agg_task_sample_size > 0 then
+		local avg = agg_task_sample_total / agg_task_sample_size
+		memusg = memusg + (avg * agg_task_count)
+	end
 end
 return memusg
 `)