Hi Akriti,
From your post I understand that its just a Single IDOC...or are you grouping the IDOCs at sender side?
If its just a single IDOC, I am not sure if there exists some std function to split it into multiple (even if you split it context might get lost)
As suggested in one of the post you can try to write the IDOC XML into Al11 dir and let PI pick the file in chunk mode (but here also context will be lost)
In your case, if you post 30MB / 90MB IDOC are you getting any error / performance effect in PI / Whats ur PI version / did u using AAE - ICO and test?
You can suggest the Sender to trim /filter / send only the required Segments in IDOC instead of handling it in PI.
Regards,
Azhar