add spend-queue-troubleshooting docs (#19659)

* add spend-queue-troubleshooting docs

* adjust spend-queue-troubleshooting docs

docs/my-website/docs/troubleshoot/spend_queue_warnings.md

@@ -0,0 +1,46 @@
+# Spend Update Queue Full Warnings
+
+## Overview
+
+The "Spend update queue is full" warning occurs in high-volume LiteLLM proxy deployments when the internal spend tracking queue reaches capacity. This is a protective mechanism to prevent memory issues during traffic spikes.
+
+## Warning Message
+
+```
+WARNING:litellm.proxy.db.db_transaction_queue.spend_update_queue:Spend update queue is full. Aggregating entries to prevent memory issues.
+```
+
+## Root Cause
+
+The spend update queue has a default maximum size of 10,000 entries (`MAX_SIZE_IN_MEMORY_QUEUE=10000`). When this limit is reached:
+
+1. New spend tracking entries are aggregated instead of queued individually
+2. This prevents memory exhaustion but may slightly delay spend updates
+3. The warning indicates your deployment is processing requests faster than the database can handle spend updates
+
+## Solutions
+
+### 1. Increase Queue Size
+
+Set the `MAX_SIZE_IN_MEMORY_QUEUE` environment variable to a higher value:
+
+```bash
+MAX_SIZE_IN_MEMORY_QUEUE=50000
+```
+
+**Tradeoffs:**
+Higher queue sizes store more items in memory - provision at least 8GB RAM for large queues
+- Recommended for deployments with consistent high traffic
+
+### 2. Horizontal Scaling
+
+Deploy multiple proxy instances with load balancing. This distributes the spend tracking load across multiple queues, reducing the pressure on any single instance's spend update queue.
+
+
+
+## Related Configuration
+
+```yaml
+# Environment variables
+MAX_SIZE_IN_MEMORY_QUEUE: 10000  # Default queue size
+```

docs/my-website/sidebars.js

@@ -1017,6 +1017,7 @@ const sidebars = {
       items: [
         "troubleshoot/cpu_issues",
         "troubleshoot/memory_issues",
+        "troubleshoot/spend_queue_warnings",
       ],
     },
   ],