Compute Budget

Compute unit limit

Each instruction is allocated a default of 200,000 CUs, and each transaction is capped at 1,400,000 CUs. When no explicit SetComputeUnitLimit instruction is present, the default is calculated based on instruction type:

default_cu_limit = (num_non_migratable_builtin_instructions * 3,000)
                 + (num_not_migrated_builtin_instructions * 3,000)
                 + (num_non_builtin_instructions * 200,000)
                 + (num_migrated_builtin_instructions * 200,000)

• Builtin instructions (System Program, Stake, Vote, etc. that have not been migrated to SBF): each allocated MAX_BUILTIN_ALLOCATION_COMPUTE_UNIT_LIMIT = 3,000 CUs (per SIMD-0170).
• Non-builtin instructions (user-deployed SBF programs): each allocated DEFAULT_INSTRUCTION_COMPUTE_UNIT_LIMIT = 200,000 CUs.
• Migrating builtins that have completed migration to SBF (feature-gated): treated as non-builtin (200,000 CUs each).

The result is clamped to MAX_COMPUTE_UNIT_LIMIT (1,400,000).

You can override this default by including a SetComputeUnitLimit instruction in your transaction.

To determine the appropriate CU limit:

1. Simulate the transaction to measure CU consumption.
2. Add a 10% safety margin to the simulated value.

Compute budget instructions

The Compute Budget Program (ComputeBudget111111111111111111111111111111) has four instructions.

Source: ComputeBudgetInstruction enum

Constraints and error conditions

The following rules apply when processing compute budget instructions:

• One per type: only one of each instruction variant is allowed per transaction. Including duplicates causes a DuplicateInstruction error (the entire transaction fails).
• RequestHeapFrame: the value must be between MIN_HEAP_FRAME_BYTES (32 KiB) and MAX_HEAP_FRAME_BYTES (256 KiB), and must be a multiple of 1,024. Otherwise the transaction fails with InvalidInstructionData. The heap size applies to every program invoked in the transaction (including CPIs).
• SetComputeUnitLimit: any u32 value is accepted. The effective limit is clamped to MAX_COMPUTE_UNIT_LIMIT (1,400,000).
• SetComputeUnitPrice: any u64 value is accepted (0 to u64::MAX).
• SetLoadedAccountsDataSizeLimit: the value must be greater than 0 (NonZeroU32). A value of 0 causes InvalidLoadedAccountsDataSizeLimit. The effective limit is clamped to MAX_LOADED_ACCOUNTS_DATA_SIZE_BYTES (64 MiB).
• Unrecognized data: any instruction sent to the Compute Budget Program that does not deserialize to a known variant fails with InvalidInstructionData.

Scheduler cost model

The validator's scheduler uses a cost model to estimate transaction resource usage before execution. These pre-execution cost estimates determine whether a transaction fits within the block's remaining capacity. They are separate from the CU metering that happens during execution.

The total scheduler cost is the sum of five components (UsageCostDetails::sum):

total_cost = signature_cost
           + write_lock_cost
           + data_bytes_cost
           + programs_execution_cost
           + loaded_accounts_data_size_cost

Cost components

All values are in compute units.

Scheduler cost constants

Vote transaction cost

Vote transactions use a static cost of 3,428 CUs regardless of their actual content.

Block limits

The scheduler enforces per-block limits. If adding a transaction would exceed any limit, it is not included in the block.

Execution budget constants

The following constants from execution_budget.rs define runtime limits during transaction execution: