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limit by-root requests to non-finalized blocks #3293

Merged
merged 2 commits into from
Jan 21, 2022
Merged

limit by-root requests to non-finalized blocks #3293

merged 2 commits into from
Jan 21, 2022

Commits on Jan 20, 2022

  1. limit by-root requests to non-finalized blocks 

    Presently, we keep a mapping from block root to `BlockRef` in memory -
this has simplified reasoning about the dag, but is not sustainable with
the chain growing.

We can distinguish between two cases where by-root access is useful:

* unfinalized blocks - this is where the beacon chain is operating
generally, by validating incoming data as interesting for future fork
choice decisions - bounded by the length of the unfinalized period
* finalized blocks - historical access in the REST API etc - no bounds,
really

In this PR, we limit the by-root block index to the first use case:
finalized chain data can more efficiently be addressed by slot number.

Future work includes:

* limiting the `BlockRef` horizon in general - each instance is 40
bytes+overhead which adds up - this needs further refactoring to deal
with the tail vs state problem
* persisting the finalized slot-to-hash index - this one also keeps
growing unbounded (albeit slowly)

Anyway, this PR easily shaves ~128mb of memory usage at the time of
writing.

* No longer honor `BeaconBlocksByRoot` requests outside of the
non-finalized period - previously, Nimbus would generously return any
block through this libp2p request - per the spec, finalized blocks
should be fetched via `BeaconBlocksByRange` instead.
* return `Opt[BlockRef]` instead of `nil` when blocks can't be found -
this becomes a lot more common now and thus deserves more attention
* `dag.blocks` -> `dag.forkBlocks` - this index only carries unfinalized
blocks from now - `finalizedBlocks` covers the other `BlockRef`
instances
* in backfill, verify that the last backfilled block leads back to
genesis, or panic
* add backfill timings to log
* fix missing check that `BlockRef` block can be fetched with
`getForkedBlock` reliably
* shortcut doppelganger check when feature is not enabled
* in REST/JSON-RPC, fetch blocks without involving `BlockRef`
    @arnetheduck
    arnetheduck committed Jan 20, 2022
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  2. fix dag.blocks ref

    @arnetheduck
    arnetheduck committed Jan 20, 2022
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