The main and most important use of transaction hashes in Bitcoin is to ensure that, when blocks are mined, the transactions contained within those blocks are locked in and any modification of those transactions can be detected and rejected. Transaction malleability is meant to change the hash of the transaction, because that ensures no-one can mutate transactions after they're in a block. If you really need to track transactions in the way MtGox is doing, you should construct your own transaction ID that hashes everything except the scriptSigs (which are malleable).
> Transaction malleability is meant to change the hash of the transaction, because that ensures no-one can mutate transactions after they're in a block.
Huh?
> If you really need to track transactions in the way MtGox is doing, you should construct your own transaction ID that hashes everything except the scriptSigs (which are malleable).
Yeah. Except the Bitcoin network also apparently produces its own hashes of transactions and those hashes include mutable data leading to undesirable situations like hash(txn1) != hash(txn2) even though txn1 == txn2. It's like hashing people by their name and age instead of name and date of birth. Next year you won't find them in your table because their age is different.
