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From "Ivan Rakov (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (IGNITE-6334) Throttle writing threads during ongoing checkpoint with token bucket algorithm
Date Mon, 11 Sep 2017 12:38:00 GMT

     [ https://issues.apache.org/jira/browse/IGNITE-6334?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Ivan Rakov updated IGNITE-6334:
    Attachment: opsec3.PNG

> Throttle writing threads during ongoing checkpoint with token bucket algorithm
> ------------------------------------------------------------------------------
>                 Key: IGNITE-6334
>                 URL: https://issues.apache.org/jira/browse/IGNITE-6334
>             Project: Ignite
>          Issue Type: Improvement
>          Components: persistence
>    Affects Versions: 2.1
>            Reporter: Ivan Rakov
>             Fix For: 2.3
>         Attachments: opsec3.PNG
> We've received several negative pieces of feedback about LFS performance with enabled
persistence. Ignite node stops responding to user operations under intensive load. Typical
operations/second graph is attached. Zero dropdowns happen during ongoing checkpoint when
checkpoint buffer (memory segment that accumulates old versions of dirty pages that are not
yet written in current checkpoint) is overflowed.
> In general, performance decrease is inevitable - writing in memory is always faster than
writing to disk. Though, we can avoid zero dropdowns if we'll throttle threads that generate
dirty pages.
> We can manage amount of throttle time with tocken bucket algorithm:
> 1) Before checkpoint start, we calculate ratio K = (number of checkpoint pages) / (size
of checkpoint buffer) and initialize non-negative atomic marker counter
> 2) Every checkpointing thread increments marker counter once per K written pages
> 3) Any thread that makes page dirty should decrement marker counter. Thread should wait
if marker counter is zero.
> Such algorithm makes buffer overflow impossible. If activity is intensive and constant,
user threads will write at the speed of the disk. On the other hand, user threads will write
at maximum speed in case of burst activity.

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