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https://issues.apache.org/jira/browse/ASTERIXDB-2600?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Chen Luo resolved ASTERIXDB-2600.
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Resolution: Implemented
> Introduce ConcurrentMergePolicy
> -------------------------------
>
> Key: ASTERIXDB-2600
> URL: https://issues.apache.org/jira/browse/ASTERIXDB-2600
> Project: Apache AsterixDB
> Issue Type: Improvement
> Reporter: Chen Luo
> Assignee: Chen Luo
> Priority: Major
>
> The default PrefixMergePolicy has a number of problems: it only schedules 1
> merge at a time; it stops merging components when they are too large. Both
> problems will lead to undesirable performance behavior. This issue introduces
> a ConcurrentMergePolicy that fixes these problems.
> It has the following four parameters:
> * minComponentMergeCount: the minimum number of components to trigger a merge
> * maxComponentMergeCount: the maximum number of components per merge
> * maxComponentCount: the maximum number of components tolerated in total;
> when this number is reached, flush will be stopped
> * sizeRatio: a merge is scheduled if the size of the oldest component <=
> sizeRatio * total size of youngest components. A larger size ratio(>1)
> implies fewer merges, but this leads to more components. A smaller size ratio
> (<1) implies more merges, but this improves query performance and space
> utilization.
> Concurrent merges will be scheduled as well. Given a sequence of components
> ordered by newest to oldest, this policy first finds a longest prefix of this
> sequence so that no component is being merged. The merge decision will then
> be based on this prefix.
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