Pruning strategy keep_n fails to reduce database size during client genesis sync

[peternose]

The pruning strategy keep_n doesn't work when syncing a client from genesis. The consensus block store located in data/consensus/data/blockstore.badger.db is never pruned, resulting in the database occupying more than 100GB of space during a mainnet sync.

One would expect this code to prune blocks, but this only occurs when a commit is finalized, not when a client processes older blocks. Restarting the client does not prune either.

Configuration:

consensus:
  prune:
    strategy: keep_n
    num_kept: 10
  checkpointer:
    disabled: true

How to prune blocks manually:

import (
	cmtstore "github.com/cometbft/cometbft/store"
	tmBadger "github.com/oasisprotocol/oasis-core/go/consensus/cometbft/db/badger"
)

func main() {
    n := 10
    tmDb, _ := tmBadger.New("data/consensus/data/blockstore.badger.db", true)
    tmBlkStore := cmtstore.NewBlockStore(tmDb)
    tmBlkStore.PruneBlocks(tmBlkStore.Height() - n)
}