stable-25-3-1: Fix alter volume in keyvalue api (#29850)

Author: maximyurchuk

ydb/core/grpc_services/rpc_keyvalue.cpp

@@ -633,7 +633,9 @@ class TAlterVolumeRequest
         modifyScheme->SetOperationType(NKikimrSchemeOp::EOperationType::ESchemeOpAlterSolomonVolume);
         tableDesc = modifyScheme->MutableAlterSolomonVolume();
         tableDesc->SetName(name);
-        tableDesc->SetPartitionCount(req->alter_partition_count());
+        if (req->alter_partition_count()) {
+            tableDesc->SetPartitionCount(req->alter_partition_count());
+        }
 
         if (GetProtoRequest()->has_storage_config()) {
             tableDesc->SetUpdateChannelsBinding(true);

ydb/core/tx/schemeshard/schemeshard__operation_alter_solomon.cpp

@@ -243,7 +243,7 @@ class TAlterSolomon: public TSubOperation {
                 return result;
             }
 
-            if (alter.GetPartitionCount() == solomon->Partitions.size()) {
+            if (alter.GetPartitionCount() == solomon->Partitions.size() && !alter.HasStorageConfig()) {
                 result->SetError(NKikimrScheme::StatusSuccess, "solomon volume has already the same shards as requested");
                 return result;
             }

ydb/services/keyvalue/grpc_service_ut.cpp

@@ -809,11 +809,16 @@ Y_UNIT_TEST_SUITE(KeyValueGRPCService) {
             UNIT_ASSERT_VALUES_EQUAL(channel.media(), "ssd");
         }
 
-        AlterVolume(channel, tablePath, 3, describeVolumeResult.storage_config());
+        ui32 currentChannelCount = describeVolumeResult.storage_config().channel_size();
+        Ydb::KeyValue::StorageConfig storageConfig = describeVolumeResult.storage_config();
+        auto newChannel = storageConfig.add_channel();
+        newChannel->set_media("ssd");
+
+        AlterVolume(channel, tablePath, 2, storageConfig);
         describeVolumeResult = DescribeVolume(channel, tablePath);
-        UNIT_ASSERT_VALUES_EQUAL(3, describeVolumeResult.partition_count());
+        UNIT_ASSERT_VALUES_EQUAL(2, describeVolumeResult.partition_count());
         UNIT_ASSERT(describeVolumeResult.has_storage_config());
-        UNIT_ASSERT_VALUES_EQUAL(describeVolumeResult.storage_config().channel_size(), 3);
+        UNIT_ASSERT_VALUES_EQUAL(describeVolumeResult.storage_config().channel_size(), currentChannelCount + 1);
         for (const auto& channel : describeVolumeResult.storage_config().channel()) {
             UNIT_ASSERT_VALUES_EQUAL(channel.media(), "ssd");
         }