[jira] [Created] (IGNITE-5875) Implement memory metric that will signal about uneven distribution of pages between segments of durable memory

["Ivan Rakov (JIRA)" <ji...@apache.org>]

Ivan Rakov created IGNITE-5875:
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             Summary: Implement memory metric that will signal about uneven distribution of pages between segments of durable memory
                 Key: IGNITE-5875
                 URL: https://issues.apache.org/jira/browse/IGNITE-5875
             Project: Ignite
          Issue Type: Improvement
          Components: persistence
    Affects Versions: 2.1
            Reporter: Ivan Rakov
             Fix For: 2.2


When persistence is enabled, we split memory policy into K equal segments (K = concurrency level). We calculate hash of pageId to determine segment where page will be stored.
Pages eviction to disk starts when segment is full. If hash function is bad enough, one segment can overflow when there are lots of free space, and evictions can start too early. We want to be able to distinguish such situations. 
Proposed name for metrics: pageHashFunctionScore
Proposed formula: difference between maximum and minimum percentage of segment fill



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