Resolving the SQL Server Error 35206: A Complete Guide

Resolving the SQL Server Error 35206: A Complete Guide

The SQL Server Error 35206 is common among server with high transactions. Most admins report of this error when transitioning from a Linux-based Oracle database to Microsoft’s SQL databases. The error dampens the entire process and creates unwanted delays.

You’ll most likely receive the following error message:

A connection timeout has occurred on a previously established connection to availability replica ‘bobtest’ with id [availability group id]. Either a networking or a firewall issue exists or the availability replica has transitioned to the resolving role.
To make things even more complicate, the Server Error 35206 can also occur under the Always On Error 35201. This happens when you fail to establish connection with one of the availability groups. But under the surface, it’s the 35206 connection timeout error that’s causing the problem.

In such cases, the error message will be the following:

A connection timeout has occurred while attempting to establish a connection to availability replica ‘bobtest’ with id [availability group id]. Either a networking or firewall issue exists, or the endpoint address provided for the replica is not the database mirroring endpoint of the host server instance.
Why the SQL Server Error 35206 and Error 35201 Occur?

The root cause of both the errors is a connection timeout error that happens between two or more corresponding replicas. Here are the reasons why that may happen:
  • The availability databases do not synchronize data, thus leading to data losss
  • On the primary replica, the logfile starts to grow to a point which can result in an outage. If left unchecked, it will lead to the error
  • Excessive alerts for critical systems that are not addressed
To fix this issue, we recommend performing a cumulative update from Microsoft. At times this helps, and other times it doesn’t. If it doesn’t, then proceed to the next section.

Fixing the Always On Connection Timeout SQL Error 35206

You’ll get the Always On Connection Timeout Error 35206 on high-end systems that have 24 core CPU working alongside a SQL server.

When you get the error, your best option is to restart the SQL Server service on the secondary replica. It’s important to not start it on primary replica.

Doing so will resolve the connectivity issue, thus fixng the Always On Connection Timeout SQL Error 35206.

There are other troubleshooting tips you should know. These are:

Use Default Network Packet Size

In many cases, admins increase the default value set for the network packet size in the pursuit to improve throughput. But this does lead to timeout errors at times. Microsoft recommends that you stick to the default values.

If you’ve changed the network packet size, then here are the steps to return to the default values:
  • Open SSMS and connect to the SQL Server Instance
  • Right-click on the SQL Server Instance and then click on Properties
  • Click on Advanced tab and change the value to default, which is 4096
  • Click on OK
Review the Connection Timeout Setting

The final troubleshooting tip is to review the connection timeout setting. You need to make sure that the session timeout setting for the Always On configuration is set to 10 seconds or more. Anything less than that would likely to cause issues.

In case the session timeout is slow between the replicas, you can gradually increase its value. You can do that in SQL Server Management Studio. Here are the steps you need to follow:
  • Open SSMS and connect to primary replica
  • After the connection is established, expand the folders
  • Click on the ‘+’ sign and expand the following two nodes:
  • High availability
  • Availability Groups
  • Next, you need to locate and select the corresponding availability groups
  • Look out for the relevant availability replica and right-click on it
  • Select Properties
  • Enter a new value in the Availability Replica Properties dialog log for session timeout period. It’s recommended to keep the value at 10 and then increase gradually
So that’s how you resolve the SQL Server Error 35206. It’s a timeout error are requires you to make a few modification to the existing configuration. If problem persists, contact the hosting support team.
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