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Flow control gates threshold value: 8192

yogi gollapudi 1 Reputation point
2021-02-11T21:35:31.727+00:00

Flow control gates threshold value: 8192 in availability groups. I found this value in Microsoft Learn during troubleshooting an AG secondary sync issue. can someone help me to understand what is 8192 messages and what will be the size of each message?

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  1. CathyJi-MSFT 21,106 Reputation points Microsoft Vendor
    2021-02-12T02:08:30.617+00:00

    Hi @yogi gollapudi ,

    > can someone help me to understand what is 8192 messages and what will be the size of each message?

    This means the total number of log messages limit at the transport or Replica level is 8192. The log block messages are sent from the Primary to the Secondary.

    When a log block is captured, every message sent over the wire has a Sequence Number which is a monotonically increasing number. Each packet also includes an acknowledgement number which is the sequence number of the last message received /processed at the other side of the connection. With these two numbers, the number of outstanding messages can be calculated to see if there exists a large number unprocessed messages.

    Please refer to the MS blog Flow Control in Always On Availability Groups – what does it mean and how do I monitor it to get the detail information.

    If the response is helpful, please click "Accept Answer" and upvote it, thank you.

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