I want to copy many many rows (maybe tens of millions) from one table to another using:
insert into table A select * from B
I am not very sure about HANA internals. Do I need to worry about transaction log is too big for above insert select?
The transaction log volume in SAP HANA will grow as required if data is changed at a higher rate than the log area gets backed up. Once log data had been backed up the corresponding log area can and will be automatically reused.
Practically speaking, if your system either has automatic log backup set up or is running with log mode override then no amount of data change should lead into too much data change issues.