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From kurt greaves <>
Subject Re: performance penalty of add column in CQL3
Date Tue, 25 Jul 2017 23:44:13 GMT
If by "offline" you mean with no reads going to the nodes, then yes that
would be a *potentially *safe time to do it, but it's still not advised.
You should avoid doing any ALTERs on versions of 3 less than 3.0.14 or 3.11
if possible.

Adding/dropping a column does not require a re-write of the data and it is
relatively efficient (it should take seconds, not hours). It's just a
schema change, so just requires gossip to propagate the schema between the
nodes. Note that if you drop a column all the data in that column is not
actually removed from the SSTables until they are compacted. I believe they
are effectively treated as tombstones if you hit the dropped column (not
sure if that's how the metrics record them though).‚Äč

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