Overloaded errors

YDB returns OVERLOADED errors in the following cases:

• Overloaded table partitions with over 15000 queries in their queue.

• The outbound CDC queue exceeds the limit of 10000 elements or 125 MB.

• Table partitions in states other than normal, for example partitions in the process of splitting or merging.

• The number of sessions with a YDB node has reached the limit of 1000.

Diagnostics

1. Open the DB overview Grafana dashboard.

2. In the API details section, see if the Soft errors (retriable) chart shows any spikes in the rate of queries with the OVERLOADED status.

   

3. To check if the spikes in overloaded errors were caused by exceeding the limit of 15000 queries in table partition queues:

   1. In the Embedded UI, go to the Databases tab and click on the database.

   2. On the Navigation tab, ensure the required database is selected.

   3. Open the Diagnostics tab.

   4. Open the Top shards tab.

   5. In the Immediate and Historical tabs, sort the shards by the InFlightTxCount column and see if the top values reach the 15000 limit.

4. To check if the spikes in overloaded errors were caused by tablet splits and merges, see Excessive tablet splits and merges.

5. To check if the spikes in overloaded errors were caused by exceeding the 1000 limit of open sessions, in the Grafana DB status dashboard, see the Session count by host chart.

6. See the overloaded shards issue.

Recommendations

If a YQL query returns an OVERLOADED error, retry the query using a randomized exponential back-off strategy. The YDB SDK provides a built-in mechanism for handling temporary failures. For more information, see Handling errors.

Exceeding the limit of open sessions per node may indicate a problem in the application logic.