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https://issues.apache.org/jira/browse/CASSANDRA-5746?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13705205#comment-13705205
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Jonathan Ellis commented on CASSANDRA-5746:
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If we want it to be fast enough for monitoring use, we need to denormalize the
count. So the question is, do we use a Counters table, a normal int table with
manual lock-and-read-before-write, or just one-off it with AtomicInteger and
sync to disk occasionally?
Personally I'd be inclined towards the last; it's okay if under- or over-count
(because of periodic CL sync for instance), as long as we reliably distinguish
between zero and non-zero hints for a given target. We could sanity check that
with an approach like listEndpointsPendingHints on startup, which would be
fairly low-overhead.
> HHOM.countPendingHints is a trap for the unwary
> -----------------------------------------------
>
> Key: CASSANDRA-5746
> URL: https://issues.apache.org/jira/browse/CASSANDRA-5746
> Project: Cassandra
> Issue Type: Bug
> Components: Core, Tools
> Reporter: Jonathan Ellis
> Assignee: Tyler Hobbs
> Fix For: 2.0.1
>
>
> countPendingHints can OOM the server fairly easily since it does a per-target
> seq scan without paging.
> More generally, countPendingHints is far too slow to be useful for routine
> monitoring.
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