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https://issues.apache.org/jira/browse/CASSANDRA-20149?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Maxim Muzafarov updated CASSANDRA-20149:
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Authors: Maxim Muzafarov, Stefan Miklosovic (was: Stefan Miklosovic)
> nodetool listsnapshots initiates two jmx calls unnecessarily
> ------------------------------------------------------------
>
> Key: CASSANDRA-20149
> URL: https://issues.apache.org/jira/browse/CASSANDRA-20149
> Project: Apache Cassandra
> Issue Type: Improvement
> Components: Local/Snapshots
> Reporter: Stefan Miklosovic
> Assignee: Stefan Miklosovic
> Priority: Normal
> Fix For: 5.x
>
> Time Spent: 2.5h
> Remaining Estimate: 0h
>
> listsnapshots calls jmx on two occasions
> 1) when getting trueSnapshotsSize
> 2) when getting snapshot details
> What it was doing in practice before CASSANDRA-18111 was that it was
> essentially loading the snapshots twice hence almost double the time to list.
> What it is doing after CASSANDRA-18111 is that it still resolves sizes but in
> a way more efficient way however it still calls jmx twice which is not
> necessary.
> The fix consists of returning resolved sizes together with snapshot details
> and then on the client size we just display and sum it up in case of wanting
> to know the total.
> It is more optimal to just return results in one response and sum few numbers
> on the client from the results than to call jmx twice.
> It is, actually, safer too. Because for now, total true snapshots size is
> returned _before_ we list snapshots. So what can happen, albeit quite
> improbably, is that a snapshot can be removed _after_ we call total true
> snapshot size method but _before_ we list all snapshots. So that means that
> total true disk size would be bigger than the sum of true disk sizes for all
> snapshots after one of them was removed.
> This also means that a user will get true raw size (raw means not human
> friendly, human friendly is returned in the response already) of a snapshot
> in the result of snapshot details automatically. They do not need to call
> extra MBean method for that (which this patch opportunistically introduces
> too).
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