Remove txindex from bitcoin config

[rootzoll]

LND does not need a index blockchain anymore (kind of missed that change). Check if its safe to remove (for other features) and get some workload off the RaspiBlitz.
lightningnetwork/lnd#751

[rootzoll]

On the first look c-lightning (for future integration) could be still in the need for a indexed blockchain. We have to take a closer look at this.

From the release notes of 0.5 RC2:

With this version of lnd, running a full node backend with a transaction index is now optional! As a result, if a user wishes to run a lighter version of their full node without the transaction index, then they're able to do so. However, for performance reasons until the persistent height hints are re-activated, we recommend running with an active transaction index for your full node which backs lnd. In either case, lnd will automatically detect if the backing full node has an active transaction index and act accordingly.

[rootzoll]

What are "persistent height hints"? if I google it I get just one result - this release notice.

The most performance problems we have on the Blitz is at the moment the blockchain (catchup) sync and the lnd scanning. If running no txindex can improve in that, it might be worth a shot - living with the compromise, that performance during regular uptime can get more slow.

It would be great if anybody can make a testrun setting up a raspiblitz with an unindexed blockchain copy on the HDD and can make some measurements.

[drunkenclam]

Im running raspiblitz with a pruned non-indexed bitcoind backend since several weeks (but on SSD, not HDD). Everything's fine so far.

[rootzoll]

@drunkenclam thx for sharing your experience

[rootzoll]

I gave this a long pondering time. I decided to keep the txindex because the RaspiBlitz should be a fullnode with all basic services on. The RaspiBlitz should provide a all "features on" platform, so that all (future) services that might need a txindex will run.

To make it more lightweight can be part of a follow up project or optional in the future.

[fluidvoice]

The RaspiBlitz should provide a all "features on" platform, so that all (future) services that might need a txindex will run.

@rootzoll This is reasonable IF the costs associated with this are low. Such as the cost to the user's time if it takes longer for IBD/syncing w/txindex, and potentially problems (ie index errors causing the script to reindex the DB). If it's not required NOW but only for future services, perhaps it's better to just do a re-download or re-index of the blockchain when the time comes that it is actually required.

[rootzoll]

Since the RaspiBolt also dropped txindex and I got feedback that even electrum server could be run without it I am open to drop txindex in a future release - see issue: #227