Persist EpochRewards sysvar #572
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Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## master #572 +/- ##
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- Coverage 81.8% 81.8% -0.1%
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Files 847 849 +2
Lines 229180 229191 +11
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- Hits 187600 187569 -31
- Misses 41580 41622 +42 |
| if slot == num_slots_in_epoch { | ||
| // cap should increase because of new epoch rewards | ||
| assert!(post_cap > pre_cap); | ||
| } else { | ||
| assert_eq!(post_cap, pre_cap); | ||
| } |
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I'm a bit confused by this check. Shouldn't the cap increase at both epoch rollovers and not just the first? ie also when slot == 2 * num_slots_in_epoch?
When I ran this locally, I saw that post_cap is only 1 lamport bigger when slot == num_slots_in_epoch, which seems a bit strange. Is it just the rent exemption for the epoch rewards sysvar account?
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Shouldn't the cap increase at both epoch rollovers and not just the first?
No. At the first block of epoch 1, the EpochRewards sysvar gets created for the first time, which increases the capitalization the amount of the sysvar's rent-exempt reserve (see below).
At the first block of epoch 2, the capitalization doesn't change: the sysvar has persisted throughout epoch 1, so no new rent-exempt reserve, and distribution starts the following block, so no new rewards.
Is it just the rent exemption for the epoch rewards sysvar account?
Correct. Sysvar lamport balances default to 1 lamport when the GenesisConfig sets Rent::free() (which it does in most of the genesis_utils fns, like create_genesis_config_with_vote_accounts()... that's a whole other issue which we can discuss separately 😅 ).
Problem
As per SIMD-0118, the reworked EpochRewards sysvar must persist between rewards periods. This will provide an easy way for on-chain programs to determine whether the rewards period is active (checking the sysvar
activefield). Meanwhile, not adjusting the sysvar's lamport balance on distribution avoids existing gymnastics around ensuring rent-exemptness and that the account is totally empty at the right time.Summary of Changes
Towards #426