This extends the `--serve-light-client-data` launch option to serve
locally collected light client data via libp2p.
Backfill of historic best `LightClientUpdate` is not yet implemented.
See https://github.com/ethereum/consensus-specs/pull/2802
During operation as a light client, the chain DAG is not available.
As a preparation, the beacon node initialization logic is divided into
parts depending on the presence of the chain DAG, and parts that are
always available (including a future light client mode).
This is a pure code move without semantic changes.
Gracefully handles the new failure modes recently introduced to the DAG
as part of https://github.com/status-im/nimbus-eth2/pull/3513
Data that is deemed to exist but fails to load leads to an error log to
avoid suppressing logic errors accidentally. In `verifyFinalization`
mode, the assertions remain active.
When eliminating orphaned forks, light client data about blocks was also
deleted when the orphaned fork was referring to a state several slots
after the block. Linking light client data pruning with block deletion
instead of state deletion fixes this problem. Light client data always
refers to blocks and their immediate post-state.
When transitioning from light client to full node the chain DAG will be
loaded separately from the rest of the beacon node initialization.
Extracting chain DAG loading to a separate function will allow reusing
a lot of the existing code. This code move doesn't change semantics.
ref loop would stop one block early in this case - trying to load
everything in one loop ends up being pretty confusing..
* simplify finalizedBlocks topup by splitting it from the head loop /
query
When doing checkpoint sync, collecting light client data of known blocks
and states incorrectly assumes that `finalized_checkpoint` information
is also known. Hardens collection to only collect finalized checkpoint
data after `dag.computeEarliestLightClientSlot`.
This file is not actually used / useful - should metadata persistence
support be added in the future, it needs to be done with a new file such
that downgrades, that have the TODO logic unimplemented, don't break.
Witout this, we end up with a massive .wal file that needs to be
checkpointed on first startup (which takes a few minutes) - it's much
more efficient to do smaller checkpoints, it turns out.
Recently, block processing times have been going up as the network grows
making early attestation riskier. Since blocks are big and attestations
are small (though numerous and therefore bandwidth-intense), it seems
better to wait a little bit longer after receiving a block, before we
publish the attestation.
Adds `LightClientProcessor` as the pendant to `BlockProcessor` while
operating in light client mode. Note that a similar mechanism based on
async futures is used for interoperability with existing infrastructure,
despite light client object validation being done synchronously.
Up til now, the block dag has been using `BlockRef`, a structure adapted
for a full DAG, to represent all of chain history. This is a correct and
simple design, but does not exploit the linearity of the chain once
parts of it finalize.
By pruning the in-memory `BlockRef` structure at finalization, we save,
at the time of writing, a cool ~250mb (or 25%:ish) chunk of memory
landing us at a steady state of ~750mb normal memory usage for a
validating node.
Above all though, we prevent memory usage from growing proportionally
with the length of the chain, something that would not be sustainable
over time - instead, the steady state memory usage is roughly
determined by the validator set size which grows much more slowly. With
these changes, the core should remain sustainable memory-wise post-merge
all the way to withdrawals (when the validator set is expected to grow).
In-memory indices are still used for the "hot" unfinalized portion of
the chain - this ensure that consensus performance remains unchanged.
What changes is that for historical access, we use a db-based linear
slot index which is cache-and-disk-friendly, keeping the cost for
accessing historical data at a similar level as before, achieving the
savings at no percievable cost to functionality or performance.
A nice collateral benefit is the almost-instant startup since we no
longer load any large indicies at dag init.
The cost of this functionality instead can be found in the complexity of
having to deal with two ways of traversing the chain - by `BlockRef` and
by slot.
* use `BlockId` instead of `BlockRef` where finalized / historical data
may be required
* simplify clearance pre-advancement
* remove dag.finalizedBlocks (~50:ish mb)
* remove `getBlockAtSlot` - use `getBlockIdAtSlot` instead
* `parent` and `atSlot` for `BlockId` now require a `ChainDAGRef`
instance, unlike `BlockRef` traversal
* prune `BlockRef` parents on finality (~200:ish mb)
* speed up ChainDAG init by not loading finalized history index
* mess up light client server error handling - this need revisiting :)
The pre-release light client sync protocol defines additional Req/Resp
messages to be made available when `--serve-light-client-data` is set.
This patch extends the `{.libp2pProtocol.}` pragma with an optional
parameter to tag such light client sync protocol specific messages.
The corresponding protocols are only selectively registered with libp2p.
The spec implicitly talks about the slot of a block in several places,
and keeping it readily available is useful in a number of context -
might as well put this implicitly refereneced helper in the spec code
directly
One more step on the journey to reduce `BlockRef` usage across the
codebase - this one gets rid of `StateData` whose job was to keep track
of which block was last assigned to a state - these duties have now been
taken over by `latest_block_root`, a fairly recent addition that
computes this block root from state data (at a small cost that should be
insignificant)
99% mechanical change.
When a `beaconBlocksByRange` response advances the `safeSlot`, but later
has errors, the sync queue keeps repeating that same request until it is
fulfilled without errors. Data up through `safeSlot` is considered to be
immutable, i.e., finalized, so re-requesting that data is not useful.
By advancing the sync progress in that scenario, those redundant query
portions can be avoided. Note, the finalized block _itself_ is always
requested, even in the initial request. This behaviour is kept same.
* fewer deps on `BlockRef` traversal in anticipation of pruning
* allows identifying EpochRef:s by their shuffling as a first step of
* tighten error handling around missing blocks
using the zero hash for signalling "missing block" is fragile and easy
to miss - with checkpoint sync now, and pruning in the future, missing
blocks become "normal".
When syncing as a light client, different behaviour is needed to handle
the various ways how errors may occur. The existing logic for blocks can
also be applied to light client objects:
- `Invalid`: Malformed object that is clearly an error by its producer.
- `MissingParent`: More data is needed to decide applicability.
- `UnviableFork`: Object may be valid but will never apply on this fork.
- `Duplicate`: No errors were encountered but the object was not useful.
Light clients require full nodes to serve additional data so that they
can stay in sync with the network. This patch adds a new launch option
`--import-light-client-data` to configure what data to make available.
For now, data is only kept in memory; it is not persisted at this time.
Note that data is only locally collected, a separate patch is needed to
actually make it availble over the network. `--serve-light-client-data`
will be used for serving data, but is not functional yet outside tests.
When performing trusted node sync, historical access is limited to
states after the checkpoint.
Reindexing restores full historical access by replaying historical
blocks against the state and storing snapshots in the database.
The process can be initiated or resumed at any point in time.
Etan Kissling
Jacek Sieka
tersec
Ștefan Talpalaru
Mamy Ratsimbazafy
dependabot[bot]
Tanguy