[lake/lance] add Flink memory usage note (#1909)

Author: xx789633

website/docs/streaming-lakehouse/integrate-data-lakes/lance.md

@@ -72,6 +72,8 @@ Additionally, when following the [Start Datalake Tiering Service](maintenance/ti
 
 > **NOTE**: Fluss v0.8 only supports tiering log tables to Lance.
 
+> **NOTE**: The Lance connector leverages Arrow Java library, which operates on off-heap memory. To prevent `java.lang.OutOfMemoryError: Direct buffer memory` error in Flink Task Manager, please increase the value of `taskmanager.memory.task.off-heap.size` in `<FLINK_HOME>/conf/config.yaml` to at least `'512m'` (e.g., `taskmanager.memory.task.off-heap.size: 512m`). You may need to adjust this value higher (such as `'1g'`) depending on your workload and data size.
+
 Then, the datalake tiering service continuously tiers data from Fluss to Lance. The parameter `table.datalake.freshness` controls the frequency that Fluss writes data to Lance tables. By default, the data freshness is 3 minutes.
 
 You can also specify Lance table properties when creating a datalake-enabled Fluss table by using the `lance.` prefix within the Fluss table properties clause.