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https://issues.apache.org/jira/browse/CASSANDRA-14297?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated CASSANDRA-14297:
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Labels: pull-request-available (was: )
> Startup checker should wait for count rather than percentage
> ------------------------------------------------------------
>
> Key: CASSANDRA-14297
> URL: https://issues.apache.org/jira/browse/CASSANDRA-14297
> Project: Cassandra
> Issue Type: Bug
> Components: Lifecycle
> Reporter: Joseph Lynch
> Assignee: Joseph Lynch
> Priority: Minor
> Labels: pull-request-available
> Fix For: 4.0
>
> Time Spent: 6h 40m
> Remaining Estimate: 0h
>
> As I commented in CASSANDRA-13993, the current wait for functionality is a
> great step in the right direction, but I don't think that the current setting
> (70% of nodes in the cluster) is the right configuration option. First I
> think this because 70% will not protect against errors as if you wait for 70%
> of the cluster you could still very easily have {{UnavailableException}} or
> {{ReadTimeoutException}} exceptions. This is because if you have even two
> nodes down in different racks in a Cassandra cluster these exceptions are
> possible (or with the default {{num_tokens}} setting of 256 it is basically
> guaranteed). Second I think this option is not easy for operators to set, the
> only setting I could think of that would "just work" is 100%.
> I proposed in that ticket instead of having `block_for_peers_percentage`
> defaulting to 70%, we instead have `block_for_peers` as a count of nodes that
> are allowed to be down before the starting node makes itself available as a
> coordinator. Of course, we would still have the timeout to limit startup time
> and deal with really extreme situations (whole datacenters down etc).
> I started working on a patch for this change [on
> github|https://github.com/jasobrown/cassandra/compare/13993...jolynch:13993],
> and am happy to finish it up with unit tests and such if someone can
> review/commit it (maybe [~aweisberg]?).
> I think the short version of my proposal is we replace:
> {noformat}
> block_for_peers_percentage: <percentage needed up, defaults to 70%>
> {noformat}
> with either
> {noformat}
> block_for_peers: <number that can be down, defaults to 1>
> {noformat}
> or, if we want to do even better imo and enable advanced operators to finely
> tune this behavior (while still having good defaults that work for almost
> everyone):
> {noformat}
> block_for_peers_local_dc: <number that can be down, defaults to 1>
> block_for_peers_each_dc: <number that can be down, defaults to sys.maxint>
> block_for_peers_all_dcs: <number that can be down, defaults to sys.maxint>
> {noformat}
> For example if an operator knows that they must be available at
> {{LOCAL_QUORUM}} they would set {{block_for_peers_local_dc=1}}, if they use
> {{EACH_QUOURM}} they would set {{block_for_peers_local_dc=1}}, if they use
> {{QUORUM}} (RF=3, dcs=2) they would set {{block_for_peers_all_dcs=2}}.
> Naturally everything would of course have a timeout to prevent startup taking
> too long.
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