In this pull request, the state iterator is implemented. It's mostly a copy-paste
from the original state snapshot package, but still has some important changes
to highlight here:
(a) The iterator for the disk layer consists of a diff iterator and a disk iterator.
Originally, the disk layer in the state snapshot was a wrapper around the disk,
and its corresponding iterator was also a wrapper around the disk iterator.
However, due to structural differences, the disk layer iterator is divided into
two parts:
- The disk iterator, which traverses the content stored on disk.
- The diff iterator, which traverses the aggregated state buffer.
Checkout `BinaryIterator` and `FastIterator` for more details.
(b) The staleness management is improved in the diffAccountIterator and
diffStorageIterator
Originally, in the `diffAccountIterator`, the layer’s staleness had to be checked
within the Next function to ensure the iterator remained usable. Additionally,
a read lock on the associated diff layer was required to first retrieve the account
blob. This read lock protection is essential to prevent concurrent map read/write.
Afterward, a staleness check was performed to ensure the retrieved data was
not outdated.
The entire logic can be simplified as follows: a loadAccount callback is provided
to retrieve account data. If the corresponding state is immutable (e.g., diff layers
in the path database), the staleness check can be skipped, and a single account
data retrieval is sufficient. However, if the corresponding state is mutable (e.g.,
the disk layer in the path database), the callback can operate as follows:
```go
func(hash common.Hash) ([]byte, error) {
dl.lock.RLock()
defer dl.lock.RUnlock()
if dl.stale {
return nil, errSnapshotStale
}
return dl.buffer.states.mustAccount(hash)
}
```
The callback solution can eliminate the complexity for managing
concurrency with the read lock for atomic operation.
This PR modifies how the metrics library handles `Enabled`: previously,
the package `init` decided whether to serve real metrics or just
dummy-types.
This has several drawbacks:
- During pkg init, we need to determine whether metrics are enabled or
not. So we first hacked in a check if certain geth-specific
commandline-flags were enabled. Then we added a similar check for
geth-env-vars. Then we almost added a very elaborate check for
toml-config-file, plus toml parsing.
- Using "real" types and dummy types interchangeably means that
everything is hidden behind interfaces. This has a performance penalty,
and also it just adds a lot of code.
This PR removes the interface stuff, uses concrete types, and allows for
the setting of Enabled to happen later. It is still assumed that
`metrics.Enable()` is invoked early on.
The somewhat 'heavy' operations, such as ticking meters and exp-decay,
now checks the enable-flag to prevent resource leak.
The change may be large, but it's mostly pretty trivial, and from the
last time I gutted the metrics, I ensured that we have fairly good test
coverage.
---------
Co-authored-by: Felix Lange <fjl@twurst.com>
This pull request ports some changes from the main state snapshot
integration one, specifically introducing the flat state tracking in
pathdb.
Note, the tracked flat state changes are only held in memory and won't
be persisted in the disk. Meanwhile, the correspoding state retrieval in
persistent state is also not supported yet. The states management in
disk is more complicated and will be implemented in a separate pull
request.
Part 1: https://github.com/ethereum/go-ethereum/pull/30752
rjl493456442
Martin HS