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I observe significant drop of backtesting performance starting today. Same scripts are executed x3-x4 longer. Any chances to be fixed?
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Mia Alissi
Hi Vasily,
Thanks for letting us know about the 3–4× slowdown you’re seeing today. In most cases, a sudden change in performance can be traced to one of three areas: 1) A temporary platform-wide congestion or maintenance window. 2) Recent edits in the algorithm itself (heavier computations, broader universes) or the introduction of a new data source that’s slower to download or process. 3) Resource limits being hit during the run (e.g., memory or CPU throttling).
Here are a few quick checks that usually help narrow it down: • Reduce the backtest scope — try a shorter date range or remove a few symbols and see if runtime improves. • Re-run an older backtest that used to complete quickly; if it now runs slowly as well, the cause is likely external to your code. • Open the backtest log and look for warnings about memory, timeouts, or data-feed errors.
It’s also a good idea to glance at the QuantConnect Announcements channel or Community Forums; if there’s a platform issue you’ll usually find other users posting about it right away.
If, after these steps, the slowdown persists and feels platform-wide, please prepare a short summary — timestamps, affected backtest or algorithm IDs, and a brief description — and send it to support@quantconnect.com. That information lets the team investigate quickly and keep you updated.
Hope this helps and that your backtests speed up again soon. Let me know how it goes!
Best,
The material on this website is provided for informational purposes only and does not constitute an offer to sell, a solicitation to buy, or a recommendation or endorsement for any security or strategy, nor does it constitute an offer to provide investment advisory services by QuantConnect. In addition, the material offers no opinion with respect to the suitability of any security or specific investment. QuantConnect makes no guarantees as to the accuracy or completeness of the views expressed in the website. The views are subject to change, and may have become unreliable for various reasons, including changes in market conditions or economic circumstances. All investments involve risk, including loss of principal. You should consult with an investment professional before making any investment decisions.
Vasily Aristarkhov
The perf has been restored, thx
Vasily Aristarkhov
Same issue again, seems really need to wait, probably some maintenance workÂ
Jared Broad
There's no known issues in backtesting speed or maintenance. Please open a support ticket with a specific project and backtest for more assistance.Â
The material on this website is provided for informational purposes only and does not constitute an offer to sell, a solicitation to buy, or a recommendation or endorsement for any security or strategy, nor does it constitute an offer to provide investment advisory services by QuantConnect. In addition, the material offers no opinion with respect to the suitability of any security or specific investment. QuantConnect makes no guarantees as to the accuracy or completeness of the views expressed in the website. The views are subject to change, and may have become unreliable for various reasons, including changes in market conditions or economic circumstances. All investments involve risk, including loss of principal. You should consult with an investment professional before making any investment decisions.
Vasily Aristarkhov
Don't have available tickets for now. Here is the performance:
The algorithm before:
2025-05-02 01:00:00 :Algorithm Id:(bb29924723ae88135ff7a02d4eef173a) completed in 6886.35 seconds at 141k data points per second. Processing total of 972,270,983 data points.Â
Version of LEAN:
Â
Launching analysis for bb29924723ae88135ff7a02d4eef173a with LEAN Engine v2.5.0.0.17206
The algorithm now (I even decreased number of processing points):
2025-05-02 01:00:00 :Algorithm Id:(a9dd323a6b2a307421215d8f0bdad3fb) completed in 25763.95 seconds at 31k data points per second. Processing total of 794,058,298 data points.Version of LEANÂ
 Launching analysis for a9dd323a6b2a307421215d8f0bdad3fb with LEAN Engine v2.5.0.0.17231Â
Â
Vasily Aristarkhov
The problem is still here, strange that nobody else complained about x3 slowdown
Vasily Aristarkhov
Any release note of last releases? at least to understand what slow down speed from 141k data point to 31k datapoints?
Vasily Aristarkhov
The material on this website is provided for informational purposes only and does not constitute an offer to sell, a solicitation to buy, or a recommendation or endorsement for any security or strategy, nor does it constitute an offer to provide investment advisory services by QuantConnect. In addition, the material offers no opinion with respect to the suitability of any security or specific investment. QuantConnect makes no guarantees as to the accuracy or completeness of the views expressed in the website. The views are subject to change, and may have become unreliable for various reasons, including changes in market conditions or economic circumstances. All investments involve risk, including loss of principal. You should consult with an investment professional before making any investment decisions.
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