Don't throw exception in case of clearing empty part. [#CLICKHOUSE-2896]

dbms/src/Storages/StorageReplicatedMergeTree.cpp

@@ -2617,11 +2617,11 @@ String StorageReplicatedMergeTree::getFakePartNameCoveringAllPartsInPartition(co
         block_number_lock.unlock();
     }
 
-    /// This should never happen.
+    /// Empty partition.
     if (right == 0)
-        throw Exception("Logical error: newly allocated block number is zero", ErrorCodes::LOGICAL_ERROR);
-    --right;
+        return {};
 
+    --right;
     return getFakePartNameCoveringPartRange(month_name, left, right);
 }
 
@@ -2636,6 +2636,12 @@ void StorageReplicatedMergeTree::clearColumnInPartition(
     String month_name = MergeTreeData::getMonthName(partition);
     String fake_part_name = getFakePartNameCoveringAllPartsInPartition(month_name);
 
+    if (fake_part_name.empty())
+    {
+        LOG_INFO(log, "Will not clear partition " << month_name << ", it is empty.");
+        return;
+    }
+
     /// We allocated new block number for this part, so new merges can't merge clearing parts with new ones
 
     LogEntry entry;
@@ -2670,6 +2676,12 @@ void StorageReplicatedMergeTree::dropPartition(const ASTPtr & query, const Field
     String month_name = MergeTreeData::getMonthName(partition);
     String fake_part_name = getFakePartNameCoveringAllPartsInPartition(month_name);
 
+    if (fake_part_name.empty())
+    {
+        LOG_INFO(log, "Will not drop partition " << month_name << ", it is empty.");
+        return;
+    }
+
     /** Forbid to choose the parts to be deleted for merging.
       * Invariant: after the `DROP_RANGE` entry appears in the log, merge of deleted parts will not appear in the log.
       */

dbms/src/Storages/StorageReplicatedMergeTree.h

@@ -468,6 +468,7 @@ private:
     void assertNotReadonly() const;
 
     /// The name of an imaginary part covering all parts in the specified partition (at the call moment).
+    /// Returns empty string if partition is empy.
     String getFakePartNameCoveringAllPartsInPartition(const String & month_name);
 
     /// Check for a node in ZK. If it is, remember this information, and then immediately answer true.

dbms/tests/queries/0_stateless/00446_clear_column_in_partition.sql

@@ -49,6 +49,12 @@ SELECT sum(data_uncompressed_bytes) FROM system.columns WHERE database='test' AN
 ALTER TABLE test.clear_column1 CLEAR COLUMN s IN PARTITION '200001';
 ALTER TABLE test.clear_column1 CLEAR COLUMN s IN PARTITION '200002';
 
+-- clear column in empty partition should be Ok
+ALTER TABLE test.clear_column1 CLEAR COLUMN s IN PARTITION '200012', CLEAR COLUMN i IN PARTITION '200012';
+-- Drop empty partition also Ok
+ALTER TABLE test.clear_column1 DROP PARTITION '200012', DROP PARTITION '200011';
+
+
 -- check optimize for non-leader replica (it is not related with CLEAR COLUMN)
 OPTIMIZE TABLE test.clear_column1;
 OPTIMIZE TABLE test.clear_column2;