update validate to ensure append-only

src/connector/src/sink/snowflake.rs

@@ -135,6 +135,11 @@ impl Sink for SnowflakeSink {
     }
 
     async fn validate(&self) -> Result<()> {
+        if !self.is_append_only {
+            return Err(SinkError::Config(
+                anyhow!("SnowflakeSink only supports append-only mode at present, please change the configuration accordingly to enable sinking.")
+            ));
+        }
         Ok(())
     }
 }
@@ -259,7 +264,7 @@ impl SnowflakeSinkWriter {
         self.epoch = epoch;
     }
 
-    /// Construct the file suffix for current sink
+    /// Construct the *unique* file suffix for the sink
     fn file_suffix(&self) -> String {
         format!("{}_{}", self.epoch, self.sink_file_suffix)
     }