Why FIX Cancel-Replace Requests Can Preserve Order Priority

Summary

The document explains why an order-management protocol distinguishes amending an existing order from canceling it and submitting a new one. A cancel-replace request can reduce the time spent waiting between cancellation and resubmission, while keeping an order active unless the amendment is rejected. That can avoid a gap in market exposure and reduce the risk of duplicate fills that may arise if a trader resubmits before a cancellation is confirmed.

The main market-microstructure benefit is that some venues may preserve an order’s place in the book for certain amendments. Venue rules determine whether priority survives; changing particular order terms can still cause the order to lose its position. The document also mentions that risk or margin checks may be faster in some systems, but this depends on the vendor. It offers conceptual explanations rather than venue-specific rules or measured latency evidence, so traders should consult the applicable exchange and API specifications before relying on priority retention or timing behavior.

Key ideas

• Cancel-replace lets a trader amend an existing order without first completing a separate cancel-and-resubmit sequence.
• Some venues may preserve book priority after eligible amendments, but venue rules govern the outcome.
• Certain changes can cause an amended order to lose its existing queue position.
• Submitting a replacement before cancellation confirmation can create a risk of overlapping fills.
• The speed of margin and risk checks depends on the implementation.

Tags

# why is there a cancel/replace message in FIX?


# why is there a cancel/replace message in FIX?












Couldn't we just cancel existing order and enter new order?

Is there any other reason apart from a communication overhead that now we need to send 2 messages vs just 1 message to cancel replace?

## Answer by amsh (score 15)

https://quant.stackexchange.com/a/20693

- Order Cancel-Replace might save you from losing priority in the book (for instance when cancelling some of the remaining shares - check the venue rules!).

- The communication overhead is very significant - it halves the round trip time (otherwise you have to cancel; wait for confirmation; re-send -- if you don't wait you risk getting double fills).

- At any given time you have your order active in the book (unless rejected).

- Margin/risk checks might also be faster (vendor-specific of course)

## Answer by NumberzQA (score 0)

https://quant.stackexchange.com/a/44182

It is aimed at maintaining order book priority based on most venues price/length/time order book priority logic. The order cancel/replace request is used to change the parameters of an existing order and the intention is not to cancel an order outright or cancel remaining quantity after a trade. Venue FIX API's are coded to see 2 distinct differences between cancel and cancel/replace. However, certain amendments to the order will cause it to lose it's place in the order book.

Shown in full with attribution under the source's licence. Licence: CC BY-SA 4.0 (Stack Exchange)

This summary was written by Stratmill's research agent from the original; it is not a copy of the source.