If currently my tables are created in rowstore and up to a point where my physical memory is insufficient due to large amount of data being ingested (with ERROR 1720), may I know is there any way to move data from memory to disk?
Not if the table was created as a rowstore. Those are always stored in-memory in MemSQL.
Columnstores are stored using a combination of memory and disk - so you could consider switching your table table (depending on your use case). We are working to give our columnstore features that allows it handle many use cases you would consider for a rowstore: https://www.memsql.com/blog/memsql-singlestore-then-there-was-one/.
If you paste your table schema here we can take a look if there are ways to reduce memory use.