---
title: "Why Rider and ReSharper Were Slow to Start, and How Microsoft Helped Fix the Problem"
description: "After ReSharper’s out-of-process (OOP) architecture launched, users reported slower Windows startup, and profiling traced the delay to Microsoft Defender scanning the separate process. Defender spends only a couple of seconds on processes in write-protected paths but can add tens of seconds when ReSharper loads DLLs from a user installation directory. The investigation used Microsoft Defender ETW logs and direct CPU-time measurements, with cold-start tests repeated 10 times inside an 8-vCPU, 8-GB Hyper-V VM; JetBrains IDEs took roughly 10–40 seconds to scan, while Microsoft IDEs and other editors stayed under one second. Collaboration with Microsoft led to Defender optimizations in version 1.449.454.0, improving scanning for ReSharper OOP and Rider in write-protected directories. JetBrains also released the Defender Performance Tool for live monitoring, offline snapshots, and CSV export."
---

# Why Rider and ReSharper Were Slow to Start, and How Microsoft Helped Fix the Problem

[Jetbrains](https://yomu.fyi/company/jetbrains) · Alexander Ulitin · Sep 9, 2026

**Type:** Explainer

## Summary

After ReSharper’s out-of-process (OOP) architecture launched, users reported slower Windows startup, and profiling traced the delay to Microsoft Defender scanning the separate process. Defender spends only a couple of seconds on processes in write-protected paths but can add tens of seconds when ReSharper loads DLLs from a user installation directory. The investigation used Microsoft Defender ETW logs and direct CPU-time measurements, with cold-start tests repeated 10 times inside an 8-vCPU, 8-GB Hyper-V VM; JetBrains IDEs took roughly 10–40 seconds to scan, while Microsoft IDEs and other editors stayed under one second. Collaboration with Microsoft led to Defender optimizations in version 1.449.454.0, improving scanning for ReSharper OOP and Rider in write-protected directories. JetBrains also released the Defender Performance Tool for live monitoring, offline snapshots, and CSV export.

## Context

ReSharper’s out-of-process architecture improved general performance, but users began reporting slower startup times on Windows. Profiling showed that Microsoft Defender scanned the separate process more extensively than the in-process arrangement, adding substantial latency to first launch.

## Approach / What changed

The investigation compared Microsoft Defender ETW scan events with direct CPU-time measurements, using repeated cold-start tests in a Hyper-V virtual machine. JetBrains collaborated with Microsoft on scanning behavior and released the Defender Performance Tool, while Microsoft shipped optimizations for ReSharper OOP and Rider in Defender version 1.449.454.0.

## Takeaways

- Microsoft Defender’s StreamScanRequestTask ETW events report scan start and end times, and those measurements were roughly equivalent to direct CPU-time measurements for this investigation.
- JetBrains IDEs required roughly 10–40 seconds of Defender scanning at cold start, while Microsoft IDEs and other editors measured under one second; command-line tools stayed under about two seconds.
- The Defender Performance Tool can monitor scan activity live, open snapshots recorded with New-MpPerformanceRecording, and export CSV data when multiple snapshots are loaded.

**Tags:** [Monitoring](https://yomu.fyi/topic/monitoring), [Performance](https://yomu.fyi/topic/performance), [Security](https://yomu.fyi/topic/security)

- Source: [Jetbrains](https://blog.jetbrains.com/dotnet/2026/09/09/why-rider-and-resharper-were-slow-to-start-and-how-microsoft-helped-fix-the-problem)
- Source URL: https://blog.jetbrains.com/dotnet/2026/09/09/why-rider-and-resharper-were-slow-to-start-and-how-microsoft-helped-fix-the-problem
- Ingested by Yomu: 2026-09-10T04:04:08.759Z

[Read original post](https://blog.jetbrains.com/dotnet/2026/09/09/why-rider-and-resharper-were-slow-to-start-and-how-microsoft-helped-fix-the-problem)