[PR] Enhance region deletion detection logic when concurrent error occurs [iotdb]

["Caideyipi (via GitHub)" <gi...@apache.org>]

Caideyipi opened a new pull request, #15160:
URL: https://github.com/apache/iotdb/pull/15160

   ## Description
   As the title said.
   
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   <hr>
   
   This PR has:
   - [ ] been self-reviewed.
       - [ ] concurrent read
       - [ ] concurrent write
       - [ ] concurrent read and write 
   - [ ] added documentation for new or modified features or behaviors.
   - [ ] added Javadocs for most classes and all non-trivial methods. 
   - [ ] added or updated version, __license__, or notice information
   - [ ] added comments explaining the "why" and the intent of the code wherever would not be obvious 
     for an unfamiliar reader.
   - [ ] added unit tests or modified existing tests to cover new code paths, ensuring the threshold 
     for code coverage.
   - [ ] added integration tests.
   - [ ] been tested in a test IoTDB cluster.
   
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   ##### Key changed/added classes (or packages if there are too many classes) in this PR
   


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Re: [PR] Enhance region deletion detection logic when concurrent error occurs [iotdb]

["Caideyipi (via GitHub)" <gi...@apache.org>]

Caideyipi commented on PR #15160:
URL: https://github.com/apache/iotdb/pull/15160#issuecomment-6410688708

   Self-review passed. The concurrent schema-region deletion path now removes the region from the map before teardown, so in-flight writes see it as unavailable; if teardown fails, the mapping is restored so deletion remains retryable. Added coverage for visibility during teardown and restoration after metadata and runtime failures.\n\nVerification: mvn -pl iotdb-core/datanode -am -Dtest=SchemaEngineDeletionTest -Dsurefire.failIfNoSpecifiedTests=false -Ddevelocity.off=true test passed on the remote test host (3 tests, 0 failures/errors); Spotless and git diff --check passed.


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Re: [PR] Enhance region deletion detection logic when concurrent error occurs [iotdb]

["Caideyipi (via GitHub)" <gi...@apache.org>]

Caideyipi commented on code in PR #15160:
URL: https://github.com/apache/iotdb/pull/15160#discussion_r4374058901


##########
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/schemaengine/SchemaEngine.java:
##########
@@ -336,20 +337,34 @@ private ISchemaRegion createSchemaRegionWithoutExistenceCheck(
     return schemaRegion;
   }
 
-  public synchronized boolean deleteSchemaRegion(SchemaRegionId schemaRegionId)
+  public synchronized boolean deleteSchemaRegion(final SchemaRegionId schemaRegionId)
       throws MetadataException {
-    ISchemaRegion schemaRegion = schemaRegionMap.get(schemaRegionId);
+    final ISchemaRegion schemaRegion = schemaRegionMap.get(schemaRegionId);
     if (schemaRegion == null) {
       logger.warn(DataNodeSchemaMessages.SCHEMA_REGION_ALREADY_DELETED, schemaRegionId);
       return false;
     }
-    schemaRegion.deleteSchemaRegion();
+    final AtomicReference<MetadataException> lastException = new AtomicReference<>();
+    // Synchronize it for region deletion detection when error occurs
+    schemaRegionMap.compute(

Review Comment:
   ConcurrentHashMap.compute keeps the existing mapping visible to lock-free getSchemaRegion() calls while the remapping function is running. Therefore, while schemaRegion.deleteSchemaRegion() is clearing the region, DataNodeRegionManager still retains the validation lock and isRegionExists() still returns true. An in-flight schema write can fail in that window and be reported as INTERNAL_SERVER_ERROR instead of the retryable NO_AVAILABLE_REGION_GROUP, which is the concurrent-deletion race this PR is intended to fix. Please publish a deletion-in-progress state (or remove the map entry before teardown and restore it on failure) so isRegionExists() observes the region as unavailable during teardown.



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