This PR introduces a node scheme abstraction. The interface is only implemented by `hashScheme` at the moment, but will be extended by `pathScheme` very soon.
Apart from that, a few changes are also included which is worth mentioning:
- port the changes in the stacktrie, tracking the path prefix of nodes during commit
- use ethdb.Database for constructing trie.Database. This is not necessary right now, but it is required for path-based used to open reverse diff freezer
It seems there is no fully typed library implementation of an LRU cache.
So I wrote one. Method names are the same as github.com/hashicorp/golang-lru,
and the new type can be used as a drop-in replacement.
Two reasons to do this:
- It's much easier to understand what a cache is for when the types are right there.
- Performance: the new implementation is slightly faster and performs zero memory
allocations in Add when the cache is at capacity. Overall, memory usage of the cache
is much reduced because keys are values are no longer wrapped in interface.
This PR reduces the amount of work we do when answering header queries, e.g. when a peer
is syncing from us.
For some items, e.g block bodies, when we read the rlp-data from database, we plug it
directly into the response package. We didn't do that for headers, but instead read
headers-rlp, decode to types.Header, and re-encode to rlp. This PR changes that to keep it
in RLP-form as much as possible. When a node is syncing from us, it typically requests 192
contiguous headers. On master it has the following effect:
- For headers not in ancient: 2 db lookups. One for translating hash->number (even though
the request is by number), and another for reading by hash (this latter one is sometimes
cached).
- For headers in ancient: 1 file lookup/syscall for translating hash->number (even though
the request is by number), and another for reading the header itself. After this, it
also performes a hashing of the header, to ensure that the hash is what it expected. In
this PR, I instead move the logic for "give me a sequence of blocks" into the lower
layers, where the database can determine how and what to read from leveldb and/or
ancients.
There are basically four types of requests; three of them are improved this way. The
fourth, by hash going backwards, is more tricky to optimize. However, since we know that
the gap is 0, we can look up by the parentHash, and stlil shave off all the number->hash
lookups.
The gapped collection can be optimized similarly, as a follow-up, at least in three out of
four cases.
Co-authored-by: Felix Lange <fjl@twurst.com>
