Prototyped experimental engine reverse downloader #7936
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AskAlexSharov
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Feb 15, 2024
Since the merge of #7936, released in version `v2.49.0` and onward, Erigon has been unable to properly download and process historical Ethereum POW blocks. This makes a mainnet sync from block 0 with snapshotting disabled (`--snapshots=false`) impossible. I discovered this issue while working on the Erigon-Pulse fork for PulseChain, but the issue remains here, and has been verified with a vanilla version of Erigon v2.57.3 against Ethereum Mainnet. ## Detail When doing a full sync from block zero with snapshotting disabled, the following error will occur: ```log [INFO] [02-08|09:06:11.859] [3/12 Senders] DONE in=7h55m24.504489889s [INFO] [02-08|09:06:11.861] [4/12 Execution] Blocks execution from=0 to=19180016 [WARN] [02-08|09:06:12.599] [4/12 Execution] Execution failed block=46274 hash=0x8252137084baebea389ddb826c4e7a63cbef2effc0d6526a5394377e5e8dada0 err="invalid block: could not apply tx 0 from block 46274 [0x669890439f5093b7dfbca9b06de1d6da78ceacf1ec0753252b3e6cf10ff81a3e]: insufficient funds for gas * price + value: address 0xdC49b9dc1AbB93Ebb856547a1C0578D65f4A32DE have 15000000000000000000 want 15024629952223800000" [INFO] [02-08|09:06:12.602] [4/12 Execution] Completed on block=46273 ``` This failure is deterministic and the process will revert back to the beginning of the `[3/12 Senders]` stage. After reprocessing senders, it will eventually fail execution on the same transaction every time. Looking into this issue, I discovered that the balance for the sender at the parent block `46273` was too low. The sender should in fact have `15156250000000000000`, enough to cover the transaction costs shown in the error message. Digging further into the history of this account, I found that the balance was too low because uncle rewards for an earlier mined block had not been properly awarded. The `15 ETH` in the chain state was the result of 3 blocks previously mined by the account, but the uncle reward of `0.15625 ETH` had not been awarded for block `2839`. **This led me to discover the issue, that uncles are being dropped entirely in the new downloader:** 1. Uncles aren't being passed from the engineapi block downloader (nil is passed). 2. Uncles aren't being considered when mapping from native types to the execution engine's GRPC types. 3. Uncles aren't being considered when mapping back from execution engine's GRPC types to the native types. 4. The header stage is lacking an implementation for `GetBlock()`, which is required for uncle verification. After passing uncles through properly, the panic() here was triggered. It's a little surprising this has gone overlooked for so long, but I suspect that almost nobody is doing a full sync w/o snapshots. It is painfully slow afterall. > *Note that because the issue originates in the downloader, once the execution failure has been encountered, the entire db must be deleted and a fresh sync started. Erigon cannot recover from the downloaded blocks being inserted into the DB w/ missing uncles.* ## Fixed This PR adds 3 commits fixing the issue. The first is a broken test, followed by the missing uncles fix which also resolves the broken test. The final commit adds the missing implementations in the header stage. This fix has been verified with a fresh sync.
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Erigon lib now good