You are viewing a plain text version of this content. The canonical link for it is here.
Posted to commits@cassandra.apache.org by "Joseph Lynch (JIRA)" <ji...@apache.org> on 2018/09/26 17:17:00 UTC
[jira] [Updated] (CASSANDRA-14297) Optional startup delay for peers
should wait for count rather than percentage
[ https://issues.apache.org/jira/browse/CASSANDRA-14297?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Joseph Lynch updated CASSANDRA-14297:
-------------------------------------
Issue Type: Bug (was: Improvement)
> Optional startup delay for peers 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: 4.0-feature-freeze-review-requested, PatchAvailable
>
> 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.
--
This message was sent by Atlassian JIRA
(v7.6.3#76005)
---------------------------------------------------------------------
To unsubscribe, e-mail: commits-unsubscribe@cassandra.apache.org
For additional commands, e-mail: commits-help@cassandra.apache.org