## Matching

The matching process for gift exchanges runs in two stages:

Potential Matching
  All the sign-ups are compared and for each person we generate a list of potential givers (people who can give them a gift), and potential recipients (people they can give a gift to). This is the slowest part of the process and can take as much as a day for a very large challenge or one where almost all the participants match each other.
Assignments
  We try to give everyone a single assignment, starting with the people who have the fewest potential givers or recipients and working up until no one else can be assigned. This process is relatively fast; it generally completes within an hour.

You may have to decide how to fix several issues that can come up during matching.

### Potential Match Issues

#### Invalid Sign-ups

Sometimes a challenge can end up with one or more invalid sign-ups -- duplicates, or sign-ups that have too many or too few offers/requests or ones that don't fit the rules of your challenge. Most commonly, this happens if someone clicks submit or update multiple times because their connection to the archive is slow. It can also happen if you have changed the rules of your challenge partway through the sign-up process -- read further for details about this.

If this happens, potential matching won't run, and you'll be quickly emailed a list of links to the invalid sign-ups so you can examine them. You can often tell easily when two sign-ups or offers/requests are duplicates, in which case you can just delete the duplicates. Sometimes you may have to contact a participant to figure out which of the sign-ups or prompts they want to use.

If on the other hand you made the rules more strict mid-stream and you have a large number of invalid sign-ups as a result, you may only be able to fix this by easing your rules to match the lowest common denominator. For instance, if you started by requiring 2 offers and 2 requests, and then upped the requirement to 3 offers and 3 requests a day into sign-up, you may have a whole slew of sign-ups that only have 2/2 and are now therefore considered invalid. To fix this, you'll have to change your challenge settings back to only requiring 2/2, while allowing 3/3.

After you have dealt with all the invalid sign-ups, you can then start matching again.