Let us assume 4 oracle12c rack instance's are running on different nodes. Each node has its own clock. No two clock shows the same time.
Which instance's timestamp is used by Oracle as SCN?
And also upon how linearization is achieved.
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I'm a bit confused. The SCN is the system change number. It's a monotonically increasing number (like a sequence) not a timestamp. The literal answer to your question is "none of them" but I suspect that doesn't answer whatever question you actually have.– Justin CaveMar 8, 2020 at 2:34
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Why are the clocks off? I believe one of the steps for setting up RAC is to set up NTP. Also, SCN has a 5sec granularity– Michael KutzMar 8, 2020 at 3:12
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1 Answer
SCN actually has a 3 second granularity now. As far as RAC goes, all cluster nodes must have synchronized clocks using NTP or some such; if the system times get too out of sync the cluster will start evicting nodes, trying to get them on the same page again. For more details on what SCN is and how it works, check these links:
