Here is a copy of the tl;dr section from an extended analysis of pubkey2index and index2pubkey cache usage provided by Navie Chan:
tl;dr: index2Pubkey is used in a lot more scenarios than pubkey2Index. The use cases for index2Pubkey do not require unfinalized information. process_deposit() is the only place in consensus spec that needs unfinalized information and it utilizes pubkey2Index.
In terms of the two-cache approach, unfinalizedIndex2Pubkey is not needed since there is not a place that utilizes it. unfinalizedPubkey2Index, however, is needed for process_deposit().
| unfinalized pubkey2Index? | unfinalized index2Pubkey? | |
|---|---|---|
| onBlock - state_transition - verify_block_signature | N/A | No |
| onBlock - state_transition - process_block - process_randao | N/A | No |
| onBlock - state_transition - process_block - process_operations - process_proposer_slashing | N/A | No |
| onBlock - state_transition - process_block - process_operations - process_attester_slashing - is_valid_indexed_attestation | N/A | No |
| onBlock - state_transition - process_block - process_operations - process_attestation - is_valid_indexed_attestation | N/A | No |
| onBlock - state_transition - process_block - process_operations - process_deposit - apply_deposit | Yes | N/A |
| onBlock - state_transition - process_block - process_operations - process_sync_aggregate - eth_fast_aggregate_verify | No | No |
| onBlock - state_transition - process_block - process_bls_to_execution_change | N/A | N/A |
| onBlock - state_transition - process_block - process_voluntary_exit | N/A | No |
| p2p - beacon_block ---- onBlock | N/A | No |
| p2p - beacon_aggregate_and_proof ---- onAttestation | N/A | No |
| p2p - voluntary_exit - process_voluntary_exit | N/A | No |
| p2p - proposer_slashing - process_proposer_slashing | N/A | No |
| p2p - attester_slashing - process_attester_slashing | N/A | No |
| p2p - beacon_attestation_{subnet_id} ---- onAttestation | N/A | No |
| p2p - sync_committee_contribution_and_proof | N/A | No |
| p2p - sync_committee_{subnet_id} | N/A | No |
| p2p - bls_to_execution_change - process_bls_to_execution_change | N/A | N/A |
| p2p - blob_sidecar_{subnet_id} - verify_blob_sidecar_signature | N/A | No |