[jira] [Commented] (CASSANDRA-6431) Prevent same CF from being enqueued to flush more than once

["Sylvain Lebresne (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-6431?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13837439#comment-13837439 ] 

Sylvain Lebresne commented on CASSANDRA-6431:
---------------------------------------------

I might misunderstand that suggestion but I would say that the fact the block writes if writes gets in faster than we're able to flush is "a feature" (to avoid OOM), even if all writes goes to the same sstable. That is, it could be that we're too agressive in blocking writes in some cases because our heuristic for "writes are faster than we can flush" is not good enough, but it's not entirely clear to me what not queuing 2 memtables for the same CF achieve (outside potentially having the memtable we don't queue grow unbounded and OOMing us that is).

> Prevent same CF from being enqueued to flush more than once
> -----------------------------------------------------------
>
>                 Key: CASSANDRA-6431
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6431
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Benedict
>            Assignee: Benedict
>            Priority: Minor
>
> As things stand we can, in certain circumstances, fill up the flush queue with multiple requests to flush the same CF, which will lead to all writes blocking until the CF is flushed. Ideally we would only enqueue each CF/Memtable once and, if requested to be flushed whilst already enqueued, mark it to be requeued once the outstanding flush completes.
> On a related note, a single table can already block writes if it has <flush queue size> or more secondary indexes. At the same time it might be worth deciding if this is also a problem and address it.



--
This message was sent by Atlassian JIRA
(v6.1#6144)