[jira] [Updated] (CASSANDRA-15367) Memtable memory allocations may deadlock

["Benedict Elliott Smith (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-15367?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Benedict Elliott Smith updated CASSANDRA-15367:
-----------------------------------------------
     Bug Category: Parent values: Availability(12983)Level 1 values: Process Crash(12992)
       Complexity: Challenging
    Discovered By: User Report
         Severity: Critical
           Status: Open  (was: Triage Needed)

> Memtable memory allocations may deadlock
> ----------------------------------------
>
>                 Key: CASSANDRA-15367
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-15367
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Local/Commit Log, Local/Memtable
>            Reporter: Benedict Elliott Smith
>            Assignee: Benedict Elliott Smith
>            Priority: Normal
>
> * Under heavy contention, we guard modifications to a partition with a mutex, for the lifetime of the memtable.
> * Memtables block for the completion of all {{OpOrder.Group}} started before their flush began
> * Memtables permit operations from this cohort to fall-through to the following Memtable, in order to guarantee a precise commitLogUpperBound
> * Memtable memory limits may be lifted for operations in the first cohort, since they block flush (and hence block future memory allocation)
> With very unfortunate scheduling
> * A contended partition may rapidly escalate to a mutex
> * The system may reach memory limits that prevent allocations for the new Memtable’s cohort (C2) 
> * An operation from C2 may hold the mutex when this occurs
> * Operations from a prior Memtable’s cohort (C1), for a contended partition, may fall-through to the next Memtable
> * The operations from C1 may execute after the above is encountered by those from C2



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