Delay initial pruning until after wallet init

[ajweiss]

Don't prune until any wallet rescanning has taken place to avoid
potentially pruning blocks that the wallet rescan may need.

Fixes #6345

[jonasschnelli]

Nice.
utACK. Have plans to test this soon.

[jonasschnelli]

Tested ACK (was hard to reproduce).

Prove (mind the rescanning before the pruning):

Opening LevelDB in /home/gitian/.bitcoinPruned/blocks/index
Opened LevelDB successfully
Opening LevelDB in /home/gitian/.bitcoinPruned/chainstate
Opened LevelDB successfully
LoadBlockIndexDB: last block file = 300
LoadBlockIndexDB: last block file info: CBlockFileInfo(blocks=159, size=113623915, heights=365157...365313, time=2015-07-13...2015-07-14)
Checking all blk files are present...
LoadBlockIndexDB: transaction index disabled
LoadBlockIndexDB: hashBestChain=00000000000000000249e73efe3b8b525bb8aca95b9abc8f8cb2287d6eaec02b height=365313 date=2015-07-14 19:24:07 progress=0.999956
init message: Verifying blocks...
Verifying last 288 blocks at level 3
No coin database inconsistencies in last 4 blocks (5533 transactions)
 block index           43301ms
init message: Loading wallet...
nFileVersion = 119900
Keys: 102 plaintext, 0 encrypted, 102 w/ metadata, 102 total
 wallet                   90ms
init message: Rescanning...
Rescanning last 325539 blocks (from block 39774)...
Still rescanning. At block 352297. Progress=0.871212
Still rescanning. At block 357888. Progress=0.929899
Still rescanning. At block 364980. Progress=0.996939
 rescan               185582ms
Unsetting NODE_NETWORK on prune mode
Prune: target=550MiB actual=405MiB diff=144MiB max_prune_height=365025 removed 298 blk/rev pairs
Prune: UnlinkPrunedFiles deleted blk/rev (00000)
Prune: UnlinkPrunedFiles deleted blk/rev (00001)
Prune: UnlinkPrunedFiles deleted blk/rev (00002)
Prune: UnlinkPrunedFiles deleted blk/rev (00003)
Prune: UnlinkPrunedFiles deleted blk/rev (00004)
Prune: UnlinkPrunedFiles deleted blk/rev (00005)
Prune: UnlinkPrunedFiles deleted blk/rev (00006)

[laanwj]

Looks good to me. utACK

[laanwj]

A small nit: this puts the pruning operation under the init message Loading Wallet, and also under Step 8: load wallet in the source code - while it has nothing to do with the wallet.
As this can take a while, and also to keep clear separation, it may be better to add an InitMessage call on top and put it in its own logical step.

[ajweiss]

SGTM. I lean towards something a little more generic like "Performing data directory maintenance..." as opposed to "Pruning blockstore..." as it would allow for other similar data directory management tasks to be added in future without creating more translation work. Although, the others aren't as generic. Do you have a preference?

[ajweiss]

Ok, pushed. I used "Pruning blockstore..." for now as it's more in line with the descriptiveness of the other init messages. If there's objection, I can change it to something more generic.

[laanwj]

@ajweiss Agreed that a more general categorization is a good idea, also to make localization easier. But yes at the moment the messages are very specific, so this is most consistent.