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Olivier Lamy commented on MBUILDCACHE-27:
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This project has moved from Jira to GitHub Issues. This issue was migrated to
[apache/maven-build-cache-extension#249|https://github.com/apache/maven-build-cache-extension/issues/249].
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> Improve efficiency of cache with plugin and source type aware processing
> ------------------------------------------------------------------------
>
> Key: MBUILDCACHE-27
> URL: https://issues.apache.org/jira/browse/MBUILDCACHE-27
> Project: Maven Build Cache Extension (Moved to GitHub Issues)
> Issue Type: Improvement
> Reporter: Alexander Ashitkin
> Priority: Major
> Labels: pull-request-available
>
> Currently build cache has implementation which checks source code and plugins
> and if it detects mismatch, whole project is rerun. This is is redundant and
> could be optimized in following cases:
> * Test code changed. In that case optimal behavior is to rerun test in an
> affected module and reuse cached artifacts in case of success. Actual
> behavior: change in a test in upstream module invalidates all downstream
> projects
> * Variation of the situation above is a test library project (aka test-jar)
> - though by convention modification is in production code, because the
> project is used only in test scope - modification of upstream test jar should
> cause just tests rerun
> * Upstream dependency changed. In that case any plugin which execution is
> not affected by upstream dependency, could be skip. Typically, it could be
> any of linter plugins - like checkstyle, which checks project source code
> only. Current behavior: plugin will rerun
> With such granular plugin and sources demarcation, it is possible to
> significantly optimize cached build time.
> To address this problem need following changes:
> * changes in build configuration to demarcate plugins as private (no need
> rebuild on dependencies change)
> * split checksum into at least 3 parts - test sources checksum, dependencies
> checksum and production checksum
> * Take into account changes in every checksum when decision of plugin
> execution is taken. If only dependencies changed, `source-code-only` plugins
> could be skipped
> * When calculating dependencies between reactor projects, take into account
> "production" checksum only. In that case changes in test code will not affect
> downstream projects
> Additional challenge is to rerun-tests-only mode - it obviously relies on
> compiled project, but probably that could be worked around by restoring
> cached jar
> Summarizing the above and applying ideas of ABI to maven build, need to
> distinguish 3 categories of project inputs:
> * implementation sources - part of the code resembling functionality shared
> within reactor (src/main and similar)
> * private sources - part which is not shared (unit test and similar)
> * dependencies - they change functionality but do not change code
> Having this 3 categories correctly represented by a separate checksums, it is
> possibly to implement optimization mentioned above.
> In target state, following behavior is desirable:
>
> ||Change||Changed project||Downstream Project||
> |Test sources|rerun tests + later plugins|Reuse cache|
> |Test dependency |rerun tests + later plugins except "source-only"
> plugins|Reuse cache|
> |Test library project|rerun everything|rerun tests|
> |Prod sources|rerun everything|Rerun everything except "source only plugins"|
> |Prod dependency|rerun everything except "source-only" plugins|Rerun
> everything except "source only plugins"|
> This behavior could be made opt-in
>
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