# [EXT] Closing an epoch

### How an epoch works
* During an epoch, investors can lock their invest and redeem orders
* All locked transactions are executed pro rata not as "first come first serve" or a queue concept
* Tinlake epochs have a minimum length but no maximum length
* Epochs can be closed after the min length is passed
* Closing an epoch requires a contract call, epochs don’t close automatically
* This contract call is an open function - anyone can do it, there is no admin required
* After an epoch is closed, the contracts check if all locked orders can be fully executed. If so, all orders are executed and the next epoch starts right away
* If not all orders can be fully executed there are three steps to close an epoch:
* Close - first transaction to initiate the end of an epoch
* Submit solution (=a viable solution needs to be submitted through a contract call which amount of each transaction type can be executed)
* [Wait till challenge period as passed] - There is a challenge period (usually 30min) to allow alternative solutions to be submitted, that may be better
* Execute epoch - after the `challenge period` has passed a third call executes the epoch and the best submitted solution

### How epochs are currently implemented

* The minimum length of an epoch is set at 24h, so an epoch will have to last at least 24h but can also last longer
* We’ve built a service/bot that crawls the pools and checks whether epochs can be closed.
1) After the minimum epoch duration of all locked pool orders has passed, the order can be fully executed - the bot closes the epoch and it is executed automatically

2) If (some of) the locked investment/redemptions orders can only be partially executed there is a manual decision by Centrifuge team or AO whether an epoch will be closed.

:::info
It does not make sense to close an epoch when only 1% of orders are executed. There are also other cases where Centrifuge team has to close epochs manually like in the example below where 55% of orders can be executed but the bot does not close epoch automatically.
:::


3) If no orders are locked the epoch will not be closed.


### Closing epochs
:::info
How to close an epoch when there locked orders can only be partially executed on Etherscan
:::

#### Tinlake UI

:::info
How to close an epoch in Tinlake UI
:::

1. Go the pool and go to the investment tab
2. When you're an admin on the pool you will see the
**close epoch button**

4. If you're not an admin you can add feature flag to the URL `/investments?show_close_epoch=true`

5. Click on close epoch button


6. Confirm transaction in Metamask


7. Epoch will be closed in the next 30 minutes

### Edge case closing epochs

If the pool is oversubscribed and the bot is disabled then closing the epoch takes two steps.
- Click on submit solution
- Click in the next steps on close epoch

Usually these steps will be executed by the bot but in case the bot does not work this has to be done manually.

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### How an epoch is currently displayed
Understand the different states of an epoch

The state uses the following structure:
1. Icon
2. Epoch number
3. State (Ongoing, ready, computing)
4. Qualification of epoch (what is executed)

| Status | Case | Consequence |
| -------- | -------- | -------- |
| Ongoing | Minimum epoch duration (24H) has not completed | Minimum duration is passed (Investors can invest, redeem) |
| Minimum duration passed | No orders locked | Epoch will not close |
| Minimum duration passed | Locked orders can be executed | Epoch closes automatically at 10AM CET |
| Minimum duration passed | Locked orders can only be partially executed | Epoch needs to be closed manually |
| Minimum duration passed | Locked orders cannot be executed | Epoch needs to be closed manually |
| Computing orders | The epoch is being executed | New epoch is started |