Hi @Chaitanya Kiran ,
Thank you for reaching out and welcome to Microsoft Q&A.
If i take log backup on the first secondary replica, does the tlog on primary replica gets truncated?
Yes! Truncation occurs automatically after performing a Transaction Log backup process, and the Transaction Log is not waiting for an active transaction or any high availability feature, such as Mirroring, Replication or Always On Availability Group, unless log truncation is delayed for some reason.
You can get more detailed information from this official document, hope this can help you well.
NOTE: The log backups on the primary will not truncate the log if ALL of the secondary replicas have not completed the processing of the log records for REDO. Please refer to this article.
Please feel free to share your issue here if you have any confusions. Your time and cooperation are much valued by us. We are looking forward to hearing from you to assist further.
Best regards,
Lucy Chen
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