huge spike in ram usage during big tx handling

[kostiamol]

HI ;)
I want to run a big tx (1.4GB when committed in redis). For this, I'm using TxPipelined + Watch.
The problem is that when the first big tx is committed and takes its 1.4Gb, the second one with the same volume fails (OOM command not allowed when used memory > 'maxmemory') although the total redis ram is 3Gb.
What can I do besides adding ram?
I think about splitting the tx into multiple ones but rollback handling would be much more complex.