Add functionality for activating a snapshot-based chainstate if one is
detected on-disk.
Also cautiously initialize chainstate cache usages so that we don't
somehow blow past our cache allowances during initialization, then
rebalance at the end of init.
Co-authored-by: Russell Yanofsky <russ@yanofsky.org>
This changes the snapshot's leveldb chainstate dir name from
`chainstate_[blockhash]` to `chainstate_snapshot`. This simplifies
later logic that loads snapshot data, and enforces the limitation
of a single snapshot at any given time.
Since we still need to persis the blockhash of the base block, we
write that out to a file (`chainstate_snapshot/base_blockhash`) for
later use during initialization, so that we can reinitialize the
snapshot chainstate.
Co-authored-by: Russell Yanofsky <russ@yanofsky.org>
This value is no longer used and is instead specified statically
in chainparams. This change means that previously generated
snapshots will no longer be usable.
This fixes an oversight from the move of nChainTx from the user-supplied
snapshot metadata into the hardcoded assumeutxo chainparams.
Since the nChainTx is now unused in the metadata, it should be removed
in a future commit.
