Memory Errors
Each entry is a symptom, its cause, and a solution.
ResourceExceededError: direct dense simulation requires N bytes
| Symptom | ResourceExceededError: plan_job: no feasible candidate -- direct dense simulation requires 17592186044416 bytes, budget is 7752519680 bytes; … |
| Cause | You asked for a statevector (or the circuit is only feasible densely), and the state needs more memory than the budget. A dense state of n qubits needs 16 · 2ⁿ bytes |
| Solution | Ask for less. Request counts or an expectation value instead, or use a smaller circuit, or split it. If the machine really has the memory, raise memory_budget_bytes (native API) |
The default budget is lower than my RAM
| Symptom | A job that "should fit" is refused |
| Cause | By default only 50% of physical memory is budgeted |
| Solution | Set RunOptions.memory_budget_bytes explicitly through the native API. MENOSBackend has no such option |
The message lists several reasons
| Symptom | A long error with several sections separated by semicolons |
| Cause | It names every candidate's refusal reason, so you can see what blocked each |
| Solution | Read each reason. A statevector request removes the stabilizer and MPS candidates ("only the dense engine can produce a statevector"), leaving only dense, which then fails on memory |
A large job is refused but I only need an expectation value
| Symptom | A big circuit fails under a statevector request |
| Cause | A statevector is 2ⁿ amplitudes regardless of what you do with it |
| Solution | Request an expectation value through MENOSEstimator. Pauli propagation, MPS, tensor-network and cut strategies avoid the full state. See Expectation Values |
The GPU ran out of memory
| Symptom | cuda: cudaMalloc failed: out of memory |
| Cause | Device memory was claimed after MENOS measured it |
| Solution | See Troubleshooting CUDA |
The process itself runs out of memory
| Symptom | The operating system kills the process |
| Cause | Memory outside what MENOS budgets: for example large counts dictionaries, statevector copies in NumPy, or other processes. MENOS budgets engine state, not your program's other allocations |
| Solution | Request less, or lower the budget to leave headroom |