00:56 < guest3423423> why do we need undo information again?

00:56 < belcher> for reorgs

00:56 < belcher> i believe

00:56 < sipa> correct

00:56 < guest3423423> but there's already raw block data

00:56 < sipa> raw block data does not tell you which outputs were spent by the block

00:56 < sipa> only which ones were added

00:57 < sipa> a block is a 'forward patch' to the UTXO set

00:57 < sipa> the undo data is a reverse patch

00:58 < guest3423423> but block's transations tell you that, no?

00:58 < sipa> no

00:59 < guest3423423> prevout?

00:59 < sipa> you have a transaction A which creates a output A1

00:59 < sipa> that tells you the hash and index which is being spent

00:59 < sipa> not the contents of the UTXO

00:59 < sipa> (the scriptPubKey and amount)

00:59 < sipa> you need to be able to restore the scriptPubKey and amount to the UTXO database

00:59 < guest3423423> of, so to avaoid indexing all the txs, we keep undo data only?

01:00 < sipa> we don't index any txn at all

01:00 < sipa> there is just a separate database with only the unspent transaction outputs

01:00 < sipa> not full transactions, not an index

01:00 < guest3423423> txindex flag, could tell you where to look it up and figure out the amounts etc

01:00 < sipa> just copies of the outputs

01:00 < sipa> that was used until bitcoin 0.7, and it became horrendously slow

01:00 < guest3423423> so it is an optimization after all?

01:00 < sipa> as you'd need to go seek all over you disk to gather all the inputs

01:01 < guest3423423> yes

01:01 < sipa> yes

01:01 < sipa> it's how the database layout is designed

01:01 < guest3423423> great. makes sense. i thought i was going crazy over this

01:01 < sipa> alternatives are certainly possible

01:01 < sipa> but they're very different

01:02 < guest3423423> that answers my question. stackoverflow could use a patch :-)

01:02 < guest3423423> to make this clearer

01:02 < sipa> link?

01:03 < guest3423423> one moment

01:05 < guest3423423> http://bitcoin.stackexchange.com/questions/32716/what-exactly-are-the-rev00000-dat-files

01:12 < guest3423423> by the way folks, when should slack be used vs freenode?

01:12 < sipa> slack is for development

01:12 < sipa> eh, freenode is

01:12 < sipa> slack is for the rest

01:13 < guest3423423> the rest?

01:14 < moli> slack is for drama

01:15 < guest3423423> that explains it :-)

01:15 < guest3423423> sipa: who do I send my job application to?

09:00 < GitHub47> [bitcoin] theuni opened pull request #8023: RFC: Interruptible threads (master...interruptible-thread) https://github.com/bitcoin/bitcoin/pull/8023