During the review of Group update Clog patch , Dilip noticed an issue with the patch where it can leak the semaphore count in one of the corner case. I have checked and found that similar issue exists for Group clear xid (ProcArrayGroupClearXid) as well. I think the reason why this problem is not noticed by anyone till now is that it can happen only in a rare scenario when the backend waiting for xid clear is woken up due to some unrelated signal. This problem didn't exist in the original commit (0e141c0fbb211bdd23783afa731e3eef95c9ad7a) of the patch, but later while fixing some issues in the committed patch, it got introduced in commit 4aec49899e5782247e134f94ce1c6ee926f88e1c. Patch to fix the issue is attached.
 - https://www.postgresql.org/message-id/CAA4eK1J%2B67edo_Wnrfx8oJ%2BrWM_BAr%2Bv6JqvQjKPdLOxR%3D0d5g%40mail.gmail.com -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
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