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https://issues.apache.org/jira/browse/HBASE-29356?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17954077#comment-17954077
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Petr Krch commented on HBASE-29356:
-----------------------------------
GitHub PR: https://github.com/apache/hbase/pull/7035
> Incorrect split behavior when region information is missing
> -----------------------------------------------------------
>
> Key: HBASE-29356
> URL: https://issues.apache.org/jira/browse/HBASE-29356
> Project: HBase
> Issue Type: Bug
> Components: Normalizer
> Affects Versions: 2.5.6, 2.6.2
> Environment: Not environment-specific — this is a clear logic bug in
> {{{}SimpleRegionNormalizer{}}}. It occurs deterministically when region size
> data is missing and can be reproduced via unit tests.
> Reporter: Petr Krch
> Priority: Major
> Labels: pull-request-available
> Attachments:
> fix-count-unknown-region-size-SimpleRegionNormalizer.patch
>
>
> We have identified a bug in the {{SimpleRegionNormalizer}} logic that leads
> to incorrect region splits when region size information is missing. If the
> size cannot be determined for one or more regions (e.g. due to unavailable
> metrics from RegionServers), the average region size calculation becomes
> incorrect. This results in a scenario where *all* regions may be considered
> too large and get split unintentionally.
> *Observed Behavior:*
> When region size data is not available (e.g., {{getRegionSizeMB()}} returns
> -1), the computed average size does not account for that, and regions with
> valid size may appear excessively large compared to the average — resulting
> in multiple unnecessary splits.
> *Expected Behavior:*
> If region size is unknown for some regions, those regions should be skipped
> during normalization. The average region size should be computed only from
> the regions for which the size is known. No region should be split or merged
> unless its size is known.
> *Patch:*
> We are submitting a patch that:
> * Skips regions with unknown size from average size computation.
> * Prevents split and merge operations on regions with unknown size.
> * Adds unit tests for scenarios with partial or total absence of size data.
> *Patch author:* Milan Vymazal <[email protected]>
> *Tests:*
> * {{testSplitOfLargeRegionIfOneIsNotKnow}} verifies correct behavior when
> one region has unknown size.
> * {{testSplitOfAllUnknownSize}} ensures that no split happens if size data
> is missing for all regions.
> *Reproduction:*
> Unfortunately, we are unable to reliably reproduce this bug in a live
> environment, since we cannot easily simulate the condition where RegionServer
> metrics are missing. However, we have confirmed the behavior through code
> analysis and the added unit tests.
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