raise_account_cu_limits (#306)

Author: bw-solana

proposals/0306-raise-account-cu-limits.md

@@ -0,0 +1,95 @@
+---
+simd: '0306'
+title: Increase writeable account limit to 20M CUs
+authors:
+  - Brennan Watt (Anza)
+category: Standard
+type: Core
+status: Review
+created: 2025-06-17
+feature: TBD
+---
+
+## Summary
+
+Increase the per account CU limit from a static 12M to 40% of the block CU limit.
+
+## Motivation
+
+This will allow more activity to target a single hot account in each block and
+take advantage of the performance improvements that have been made. We are
+consistently hitting the current 12M CU cap, so this will unlock more economic
+activity.
+
+## New Terminology
+
+No new terms, but the following definitions are given for clarity:
+
+- Max Block Units - The maximum number of CUs that can be included in a block.
+- Max Writable Account Units - The maximum number of CUs that can be used to
+  write any given account in a block.
+- Max Vote Units - The maximum number of CUs that can be used by simple votes
+  in a block.
+- Max Block Accounts Data Size Delta - The maximum size of the accounts data
+  size delta in a block.
+
+## Detailed Design
+
+The following table shows the current block limits and future proposed block
+limits:
+
+| Type | Current Block Limit | SIMD-0256 Limit | SIMD-0286 Limit |
+|------|-----|---------------|---------------------|
+| Max Block Units | 50M | 60M | 100M |
+| Max Writable Account Units | 12M | 12M  | 12M |
+| Max Vote Units | 36M | 36M  | 36M  |
+| Max Block Accounts Data Size Delta | 100MB | 100MB | 100MB |
+
+This proposal advocates to set `Max Writable Account Units` to 40% of `Max Block
+Units`. This will result in the following `Max Writable Account Units` for
+current and future proposed `Max Block Units`:
+
+| Block Limit | Max Block Units | Max Writable Account Units |
+| Current | 50M | 20M |
+| SIMD-0256 | 60M | 24M |
+| SIMD-0286 | 100M | 40M |
+
+This proposal only changes the `Max Writable Account Units` limit. The purpose
+is to increase amount of activity that can target a single account. The `Max
+Block Unit` is left unchanged. Further increases to global limit will be
+addressed with SIMD-0286. Increasing `Max Writeable Account Units` while leaving
+`Max Block Units` unchanged takes advantage of underutilized serial execution
+capacity.
+
+The intention is for this to follow SIMD-0256 but activate before SIMD-0286
+(which has not merged yet). Rationale is that we are ready to handle this
+increased serialized execution today but the 100M CU increase has some
+development dependencies. That said, we will be capable of handling a scenario
+where SIMD-0286 merges and gets activated first.
+
+## Alternatives Considered
+
+Killing per account limits altogether. But this may be too easy to attack by
+aggressively targeting a single account up to the global CU limit.
+
+## Impact
+
+This will allow for more serialized account access, making it easier for more
+updates to some hot state to occur. It may increase block execution times, which
+could impact slot times for some unforeseen cases.
+
+## Security Considerations
+
+Blocks may take longer to execute, slowing down network progress and catchup times.
+
+## Drawbacks *(Optional)*
+
+Increasing the CU limit for single account will increase worst case serialized
+execution, which could increase block verification and/or slot time.
+
+## Backwards Compatibility *(Optional)*
+
+- All previously valid blocks are still valid, since limits are only
+  increasing.
+- Blocks produced after the change may be rejected by previous versions that do
+  not support the new limits.