# EPF6 Dev Updates – Week 6

I had a very informative call with matt, my mentor from the lodestar team. We discussed on the plans for the backfill implementation and he suggested to look more into these:
- how exactly lighthouse/prysm handles reqresp messages to and from peers wrt backfill implementation
- drafting a pr for the task 2 from the backfill issue: *"Building DB Repository that will house backfill state"* ([github comment link](https://github.com/ChainSafe/lodestar/issues/7753#issuecomment-3079263617))
- dive deep into prysm codebase along with lighthouse and optionally prepare architecture design notes.
- what exactly is backfill support state of the clients and specific params such as backfill batch size (used in `beaconblocksbyrange` request) for the clients (specifically teku, lighthouse and prysm).

I explored and found out some info about some clients, noting here for future reference:

Lighthouse:
- supports blocks+blobs(upto DA boundary currently)
- backfill starts after cp_sync+fwd_sync
- [BACKFILL_EPOCHS_PER_BATCH](https://github.com/sigp/lighthouse/blob/cfb1f7331064b758c6786e4e1dc15507af5ff5d1/beacon_node/network/src/sync/backfill_sync/mod.rs#L39): 1(ie 32 slots)
- the rate can be increased by --disable-backfill-rate-limiting flag
- they are resolving some issues realated to node banning most of its peers while backfilling blobs

Prysm:
- blob backfill support prsesnt from v5.0.0(Deneb upgrade) along with block backfill support
- backfill starts after cp_sync+fwd_sync
- [related cli flags](https://github.com/OffchainLabs/prysm/blob/develop/cmd/beacon-chain/sync/backfill/flags/flags.go):
--backfill-batch-size (default: 32 slots)
--backfill-oldest-slot (default: 0)
--backfill-worker-count value (default: 2)

Teku:
- [DEFAULT_HISTORICAL_SYNC_BATCH_SIZE](https://github.com/Consensys/teku/blob/1107d9762bdbbabb8c8ae403dd53f2d213db7274/beacon/sync/src/main/java/tech/pegasys/teku/beacon/sync/SyncConfig.java#L27) = 50
- usage of DEFAULT_HISTORICAL_SYNC_BATCH_SIZE ([exalidraw link](https://excalidraw.com/#json=Whl4sjUSxDB7LkNhDEmX6,mN14eTVKbWgmiKiApDpyzg))
- [HistoricalBlockSyncService](https://github.com/Consensys/teku/blob/1107d9762bdbbabb8c8ae403dd53f2d213db7274/beacon/sync/src/main/java/tech/pegasys/teku/beacon/sync/DefaultSyncServiceFactory.java#L158)

Also started working on backfill db repo changes, will open pr soon.

Week 7 goals:
---
- draft the pr with backfill db repo changes
- deep dive lighthouse & prysm code and prepare architecture design notes