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https://issues.apache.org/jira/browse/NIFI-12206?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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David Handermann updated NIFI-12206:
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Status: Patch Available (was: In Progress)
> Refactor Flow Configuration History from H2 to JetBrains Xodus
> --------------------------------------------------------------
>
> Key: NIFI-12206
> URL: https://issues.apache.org/jira/browse/NIFI-12206
> Project: Apache NiFi
> Issue Type: Improvement
> Components: Core Framework
> Reporter: David Handermann
> Assignee: David Handermann
> Priority: Major
> Fix For: 2.latest
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> The [H2 Database Engine|https://h2database.com/html/main.html] has provided
> local persistent storage for several types of information across Apache NiFi
> versions. With multiple refactoring efforts over several versions, H2 no
> longer stores user session information or identity provider group
> information, leaving the Flow Configuration History as the only remaining
> reference to H2.
> H2 version 2.1 introduced incompatible changes in the binary storage format
> from H2 version 1.4, and H2 version 2.2 was also unable to read files from
> earlier H2 versions. These binary changes required custom migration modules
> and shaded distribution of H2 libraries to support upgrading between Apache
> NiFi versions.
> With the scope of H2 usage narrowed to Flow Configuration History in Apache
> NiFi 1.23.0 and following, the storage strategy should be changed. Apache
> Derby, SQLite, and HSQLDB are other potential options supporting file-based
> relational storage, but maintenance level and platform-specific limitations
> present concerns with these libraries.
> The [JetBrains Xodus|https://github.com/JetBrains/xodus] library provides
> persistent and scalable storage that avoids several issues present in other
> alternatives. The framework is licensed under Apache Software License Version
> 2.0 and has a narrow set of dependencies aside from the Kotlin standard
> libraries. Xodus is now in version 2.0 and has maintained format
> compatibility when upgrading between major versions.
> Based on the H2 database migration modules on the Apache NiFi support branch,
> a subsequent issue can implement automated migration from H2 to Xodus,
> providing an upgrade path from NiFi 1 to 2.
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