[jira] [Commented] (CASSANDRA-14271) The Hints web page in the web site is empty

["Kenneth Brotman (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-14271?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16381797#comment-16381797 ] 

Kenneth Brotman commented on CASSANDRA-14271:
---------------------------------------------

 

Hints in Cassandra provide a mechanism for ensuring consistency amongst replicas across configurable periods of downtime, and when replicas fail to acknowledge a write.

 

Each hint represents a single mutation which is a write made by a client. Hints are stored as flat-files on disk, and are labelled as {{<hostID>-<timestamp>-<version>.hints}}. A single file contains the stored hints for exactly one node in the cluster, based off its {{hostID}} as reported in {{nodetool status}}. A host can have multiple hint files, as there is a size limit on a single hintfile of 128MB, these are differentiated by the {{timestamp}} which is the point at which the hint file is created. {{<version>}} is the hint format version of the file. A crc file is created alongside each hint file, which covers all hints in the file.

 

By default a coordinator will store the first 3 hours of hints for a node, and this is configurable by the yaml property [max_hint_window_in_ms|https://github.com/apache/cassandra/blob/trunk/doc/latest/configuration/cassandra_config_file.html#max-hint-window-in-ms]. After a node has been down for longer than the configured window, no more hints are stored and a repair will be necessary after the node is recovered. Replayment of hints is attempted every 10 seconds, and continues until the hints are successful. If a hint fails to be replayed the position in the hint file will be reset and it will automatically be retried at the next hint replay attempt.
 +Note that a node that has been down will serve inconsistent data until all hints destined for that node are replayed, and if the node has been down longer than the configured hint window data on that node will be inconsistent until a repair has occured for the affected data.

A hint is stored for all replicas on the coordinator node in the following cases:

 
 # When a subset of replicas are down, but enough are still alive to satisfy a consistency level >= {{ONE}}.
 # When all replicas are down but the consistency level for the query was {{ANY}}.
 # When a replica that was sent the mutation doesn't acknowledge it successfully applied. I.e, the query times out.

 

A hint does not count towards the Consistency Level for any level other than [ANY|https://github.com/apache/cassandra/blob/trunk/doc/latest/architecture/dynamo.html?highlight=consistency%20level#tunable-consistency]. An INSERT at ANY will be successful as long as _at least_ one hint is written.

 

Note: the above was written by Kurt Greaves for Issue#14128

 

> The Hints web page in the web site is empty
> -------------------------------------------
>
>                 Key: CASSANDRA-14271
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-14271
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Documentation and Website
>            Reporter: Kenneth Brotman
>            Priority: Major
>
> [http://cassandra.apache.org/doc/latest/operating/hints.html]
> is empty.  Please contribute content.  Myself or someone else will take it from there.



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