---
title:  Sending Periodic Acknowledgment
---

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Servers use periodic acknowledgment to reduce the likelihood of duplicate notifications, and to reduce resource usage.

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When redundancy is enabled for high availability and `redundancy-level` is set to 1 or higher, clients send (and servers expect) periodic acknowledgment messages at configurable intervals for notifications they have received. A periodic ack is not sent by the client if there are no unacknowledged notifications at the time.

Use the following system properties in the `geode.properties` file to configure periodic ack.

<table>
<colgroup>
<col width="50%" />
<col width="50%" />
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<tbody>
<tr class="odd">
<td><code class="ph codeph">notify-ack-interval</code></td>
<td><p>Minimum period between two consecutive acknowledgment messages sent from the client to the server. The default setting (in seconds) is 10.</p></td>
</tr>
<tr class="even">
<td><code class="ph codeph">notify-dupcheck-life</code></td>
<td><p>Minimum time a client continues to track a notification source for duplicates when no new notifications arrive before expiring it. The default setting (in seconds) is 300.</p></td>
</tr>
</tbody>
</table>

The Pool API also provides attributes to configure periodic ack and duplicate message tracking timeout. See `subscription-message-tracking-timeout` and `subscription-ack-interval` in the list of pool attributes under [Configuring Pools for Servers or Locators](../connection-pools/configuring-pools.html#configuring-pools).