calculations
Since BlockHeightByHash only returns the heights for blocks that are in
the main chain, when a block that is stale gets pruned, this will cause
an error in the block height lookup and cause an error in block
processing.
Look up the node directly from the index and if the node isn't found,
just skip that node. For utxoCache.lastFlushHash, if that isn't found,
just force a flush.
On startup when the headers-first mode is off, when receiving the first
block, the periodic flush will trigger. The lastflushtime wasn't set
which resulted in the flush being triggered on the first block on
restart.
flushNeededAfterPrune returns true if the utxocache needs to be flushed
after the pruning of the given slice of block hashes. For the utxo
cache to be recoverable while pruning is enabled, we need to make sure
that there exists blocks since the last utxo cache flush. If there are
blocks that are deleted after the last utxo cache flush, the utxo set is
irrecoverable. The added method provides a way to tell if a flush is
needed.
This change is part of the effort to add utxocache support to btcd.
utxo cache is now used by the BlockChain struct. By default it's used
and the minimum cache is set to 250MiB. The change made helps speed up
block/tx validation as the cache allows for much faster lookup of utxos.
The initial block download in particular is improved as the db i/o
bottleneck is remedied by the cache.
The implemented utxocache implements connectTransactions just like
utxoviewpoint and can be used as a drop in replacement for
connectTransactions.
One thing to note is that unlike the utxoViewpoint, the utxocache
immediately deletes the spent entry from the cache. This means that the
utxocache is unfit for functions like checkConnectBlock where you expect
the entry to still exist but be marked as spent.
disconnectTransactions is purposely not implemented as using the cache
during reorganizations may leave the utxo state inconsistent if there is
an unexpected shutdown. The utxoViewpoint will still have to be used
for reorganizations.
This change is part of the effort to add utxocache support to btcd.
mapslice allows the caller to allocate a fixed amount of memory for the
utxo cache maps without the mapslice going over that fixed amount of
memory. This is useful as we can have variable sizes (1GB, 1.1GB, 2.3GB,
etc) while guaranteeing a memory limit.
