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Maximum Allowed Network Link Latency between two data-centers for SQL Always-On RRS feed

  • Question

  • Hi, 

    We are implementing SQL AL-Ways on between two data-centers and looking for network latency requirements. What is maximum allowed network latency for SQL always on group database to keep sync the database with synchronous and also for asynchronous. 

       

    Saturday, August 24, 2019 3:33 PM

All replies

  • Can any one please comment on it?
    Sunday, August 25, 2019 7:30 AM
  •  

    Hi Asif- Janjua,

     

    This does not have a specified value, you need to actually test it.  It depends on many factorslog send rateharden rateworkload and so on. The only advice I can give is to use good disks and networks. Network latency may cause the secondary replica to enter the disconnected state incorrectly.  Remember to set Session Timeout to reasonable value.

     

    Best regards,

    Dedmon Dai


    MSDN Community Support
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    Monday, August 26, 2019 8:06 AM
  • Hi Dedmon, 

    Thanks for your reply. Can you please let me know what should be letancy so network can be called as good network? 

    Monday, August 26, 2019 6:11 PM
  • There is no "generic" threshold. It depends on your configuration (sync vs. async commit), workload and amount of data loss you can tolerate.

    If you are using asynchronous commit, latency is somewhat less important. It will mainly dictate how much data you can lose. For synchronous commit it is much more complicated. Latency will contribute to blocking. Transaction remains open until ACK is received and locks are held longer. Read this blog post for more details.


    Thank you!

    Dmitri V. Korotkevitch (MVP, MCM, MCPD)

    My blog: http://aboutsqlserver.com

    Monday, August 26, 2019 8:49 PM