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https://issues.apache.org/jira/browse/HBASE-29857?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18054802#comment-18054802
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rstest commented on HBASE-29857:
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Yes I'm preparing the PR and will submit soon. Thanks for confirm it!
> BucketCache fails to start when persistence file was written with empty cache
> -----------------------------------------------------------------------------
>
> Key: HBASE-29857
> URL: https://issues.apache.org/jira/browse/HBASE-29857
> Project: HBase
> Issue Type: Bug
> Components: regionserver
> Affects Versions: 2.6.3
> Reporter: rstest
> Priority: Critical
>
> When a RegionServer with BucketCache persistence enabled is restarted, if the
> BucketCache was empty at shutdown time, the new RegionServer fails to start
> with a `NullPointerException` in `BucketCache.parsePB()`.
>
> The bug is in the interaction between `BucketProtoUtils.serializeAsPB()` and
> `BucketCache.retrieveChunkedBackingMap()`:
> 1. During shutdown with empty cache: When `backingMap.size() == 0`,
> `serializeAsPB()` writes `numChunks = 0` to the persistence file, but the
> loop that writes `BucketCacheEntry` objects never executes (because there are
> no entries to iterate). This means no BucketCacheEntry is written to the file
> 2. During startup: `retrieveChunkedBackingMap()` reads `numChunks = 0` from
> the file, but still attempts to read the first chunk using
> `parseDelimitedFrom()`. Since no `BucketCacheEntry` was written,
> `parseDelimitedFrom()` returns `null`.
> 3. NPE occurs: The null `firstChunk` is passed to `parsePB()`, which calls
> `firstChunk.getDeserializersMap()` on the null object, causing NPE.
>
> This bug just make the region server not able to be restarted.
> I will provide a fix in PR and also a unit test that can reproduce the bug
> (if the fix is not applied).
>
>
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