8000 node: call CreateSnapshot explicitly when node starts by yoomee1313 · Pull Request #1829 · klaytn/klaytn · GitHub
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node: call CreateSnapshot explicitly when node starts #1829

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merged 1 commit into from
Jun 6, 2023
Merged

node: call CreateSnapshot explicitly when node starts #1829

merged 1 commit into from
Jun 6, 2023

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yoomee1313
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@yoomee1313 yoomee1313 commented Apr 18, 2023 •
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Proposed changes

  • gov.changeSet
    • gov.changeSet is one of the governance state cache: the vote data which is not stored in governance db yet.
    • It is a memory value. So, if the node shut down before it is flushed into gov db at governance block, it is deleted.
    • but it would restored well when the node restarts during the first snapshot call.
  • However, after fix debug.traceBlock not to remove gov.changeSet #1706 is applied, missing gov.changeSet problem appears
    • if the first snapshot is called by getValidator, it creates the snapshot caches without restoring gov.changeSet (because the snapshot called by getValidator is not able to write governance data)
    • the next snapshot call skip the restoration part always whether it is able to write governance data or not because there's already snapshot cache.
    • and it leads to a verification error due to the mismatch between gov.changeSet and blockHeader.governanceData.
  • So, the solution is calling snapshot explictly before sync starts to ensure the first snapshot call restores gov.changeSet always.
    • currentSet or idxCache are restored during intializeCache, but changeSet does not.

dev

  • vote at block 34 and restart immediately
  • at the next epoch start block (e.g. 60), it returned verification error
ERROR[05/05,09:01:42 Z] [30] Verification Error                        len(receivedChangeSet)=1 len(changeSet)=0
ERROR[05/05,09:01:42 Z] [5]
########## BAD BLOCK #########
...

PR

  • vote at block 34 and restart immediately
  • at the next epoch start block (e.g. 60), it handles governance data properly with out error.

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@yoomee1313 yoomee1313 requested a review from JayChoi1736 May 16, 2023 06:12
@yoomee1313 yoomee1313 force-pushed the fix-missing-vote2 branch from 71080f4 to f3605ce Compare May 17, 2023 05:50
@yoomee1313 yoomee1313 changed the title consensus: revoke to call writable snapshot function (called by getValidators) node: call CreateSnapshot explicitly when node starts to restore votings May 17, 2023
@yoomee1313 yoomee1313 marked this pull request as ready for review May 17, 2023 06:23
@yoomee1313 yoomee1313 requested a review from aidan-kwon May 17, 2023 06:26
blukat29
blukat29 previously approved these changes May 18, 2023
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aidan-kwon
aidan-kwon reviewed May 18, 2023
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I'm sorry, but I cannot understand some points. Can you explain more?

if no such snapshot function is called until the next governance block is processed,

It seems that a node calls snapshot() on every block to verifyHeader.

this problem is caused by #1706

The PR disables "write" in some cases, but you are saying that there is an issue on "read" (restoration of vote data). So, I am confused.

aidan-kwon
aidan-kwon reviewed May 18, 2023
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It seems that a node calls snapshot() on every block to verifyHeader.

In a syncing situation, a snapshot is called, governance state data is writable, so governance state data is written(e.g. changeSet, currentSet). But the problem is that if the snapshot already exists, it will be hit and returned directly from the cache, and the code that writes the governance state data is not executed. (When I say that the snapshot already exists, I am assuming that the code has been run once when creating the snapshot.)
but the problem is, when the first snapshot call is non-writable at governance state data, the assumption the code has been run once is broken.

On second thought, I realized that �it is good to change the implementation, because the fundamental solution is to decouple the governance state data recovery (specifically changeSet) from the snapshot call.

  • implement changeSet recovery logic in initializeCache. (but if not possible, i will go back to original solution).

@yoomee1313 yoomee1313 marked this pull request as draft May 19, 2023 10:51
@yoomee1313
node: restore the snapshots of the latest synced blocks when node starts
605ca57 
- latest synced blocks are the blocks from lastGovernanceStateBlock to currentBlock
- in-memory snapshots and related gov states are missed when node stops, so restore it when node starts
@yoomee1313 yoomee1313 force-pushed the fix-missing-vote2 branch from f3605ce to 605ca57 Compare May 23, 2023 06:16
yoomee1313
yoomee1313 commented May 23, 2023
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@yoomee1313 yoomee1313 changed the title node: call CreateSnapshot explicitly when node starts to restore votings node: call CreateSnapshot explicitly when node starts May 23, 2023
@yoomee1313 yoomee1313 marked this pull request as ready for review May 30, 2023 10:29
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Dear reviewers, please review this PR one more time. I'll go as #1829 (comment).

@yoomee1313 yoomee1313 merged commit 89ed176 into klaytn:dev Jun 6, 2023
@yoomee1313 yoomee1313 deleted the fix-missing-vote2 branch June 6, 2023 01:30
@JayChoi1736 JayChoi1736 mentioned this pull request Jul 24, 2023
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