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From "Ivan Rakov (JIRA)" <j...@apache.org>
Subject [jira] [Created] (IGNITE-6334) Throttle writing threads during ongoing checkpoint with token bucket algorithm
Date Mon, 11 Sep 2017 12:35:00 GMT
Ivan Rakov created IGNITE-6334:
----------------------------------

             Summary: 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


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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