[jira] [Updated] (CASSANDRA-20800) Clarify tombstone documentation on expired TTL values

["Brad Schoening (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-20800?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Brad Schoening updated CASSANDRA-20800:
---------------------------------------
    Test and Documentation Plan: Just documentation update
                         Status: Patch Available  (was: Open)

> Clarify tombstone documentation on expired TTL values
> -----------------------------------------------------
>
>                 Key: CASSANDRA-20800
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-20800
>             Project: Apache Cassandra
>          Issue Type: Improvement
>          Components: Documentation
>            Reporter: Brad Schoening
>            Assignee: Praveen Reddy Arra
>            Priority: Low
>          Time Spent: 40m
>  Remaining Estimate: 0h
>
> In the past, I found this section of our tombstone documentation confusing. Since sstables are immutable, how does it 'mark' a row with a tombstone? If the data is expired, would it not just purge the expired row instead of marking it with a tombstone?
> It seems to be describing a special case where gc_grace_seconds > TTL and the data is compacted. For example, when the TTL is 1 day and the deafault gc_grace_seconds is the default of ten days. When this happens, expired values may be compacted and re-written with a expired flag set to True.
> My understanding is that if gc_grace_seconds <= TTL then the expired data would be purged during compaction and not generate a tombstone record.
> [Tombstones: What are tombstones?|https://cassandra.apache.org/doc/latest/cassandra/managing/operating/compaction/tombstones.html#what-are-tombstones]
> {noformat}
> Note: 
> You can also mark a Cassandra row or column with a time-to-live (TTL) value. 
> After this amount of time has ended, Cassandra marks the object with a tombstone, and handles it like other tombstoned objects.{noformat}



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