bc1ec69008
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not outdated.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.
98 lines
3.0 KiB
Go
98 lines
3.0 KiB
Go
// Copyright 2024 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package pathdb
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import (
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"github.com/ethereum/go-ethereum/common"
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"github.com/ethereum/go-ethereum/ethdb"
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)
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// holdableIterator is a wrapper of underlying database iterator. It extends
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// the basic iterator interface by adding Hold which can hold the element
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// locally where the iterator is currently located and serve it up next time.
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type holdableIterator struct {
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it ethdb.Iterator
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key []byte
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val []byte
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atHeld bool
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}
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// newHoldableIterator initializes the holdableIterator with the given iterator.
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func newHoldableIterator(it ethdb.Iterator) *holdableIterator {
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return &holdableIterator{it: it}
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}
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// Hold holds the element locally where the iterator is currently located which
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// can be served up next time.
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func (it *holdableIterator) Hold() {
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if it.it.Key() == nil {
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return // nothing to hold
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}
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it.key = common.CopyBytes(it.it.Key())
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it.val = common.CopyBytes(it.it.Value())
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it.atHeld = false
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}
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// Next moves the iterator to the next key/value pair. It returns whether the
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// iterator is exhausted.
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func (it *holdableIterator) Next() bool {
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if !it.atHeld && it.key != nil {
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it.atHeld = true
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} else if it.atHeld {
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it.atHeld = false
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it.key = nil
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it.val = nil
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}
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if it.key != nil {
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return true // shifted to locally held value
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}
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return it.it.Next()
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}
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// Error returns any accumulated error. Exhausting all the key/value pairs
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// is not considered to be an error.
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func (it *holdableIterator) Error() error { return it.it.Error() }
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// Release releases associated resources. Release should always succeed and can
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// be called multiple times without causing error.
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func (it *holdableIterator) Release() {
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it.atHeld = false
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it.key = nil
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it.val = nil
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it.it.Release()
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}
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// Key returns the key of the current key/value pair, or nil if done. The caller
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// should not modify the contents of the returned slice, and its contents may
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// change on the next call to Next.
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func (it *holdableIterator) Key() []byte {
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if it.key != nil {
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return it.key
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}
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return it.it.Key()
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}
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// Value returns the value of the current key/value pair, or nil if done. The
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// caller should not modify the contents of the returned slice, and its contents
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// may change on the next call to Next.
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func (it *holdableIterator) Value() []byte {
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if it.val != nil {
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return it.val
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}
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return it.it.Value()
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}
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