I apologize for my technical ineptitudes.

I am trying to understand how segwit saves blockchain space as that is what it is being marketed as and with a softfork in the upcoming weeks.

So i look at the BIP, I find each segwit tx needs a commitment hash, plus more. this is 32 bytes per tx that to my ignorant simple minded thinking is in addition to what would be needed if it was a normal tx.

Now I am being told that we dont need to count the space used by the witness data. This confuses me. I like to count all permanently required data as the permanent space cost.

I apologize for asking questions like this, but I am just a simple C programmer trying to allocate space for the segwit and noticing it seems to take more space for every tx. I await to be properly learned about how the commitment hash is not actually needed to be stored anywhere and how that would still allow a full node to properly validate all the transactions.

Or did I misunderstand? Does segwit mean that it is no business of full nodes to verify all the transactions?

James

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OK, it was made clear that the commitment hash is just for the wtxid calculation so it doesnt really exist anywhere. The cost is 2 bytes per tx and 1 byte per vin. Still it is increasing HDD space used permanently, which is what confused me as segwit was marketed as saving HDD space and helping with scaling