fix: derive FSP history retention from chain epoch length

Author: adg-flare

cmd/indexer/main.go

@@ -88,7 +88,7 @@ func run(ctx context.Context) error {
 	logger.Infof("Connected to chain ID %s", chainID)
 
 	if cfg.Indexer.IsFspMode() {
-		return fsp.RunIndexer(ctx, cfg, db, ethClient, resolver)
+		return fsp.RunIndexer(ctx, cfg, db, ethClient, resolver, chainID)
 	}
 
 	historyDrop, err := cfg.DB.GetHistoryDrop(ctx, chainID)

internal/fsp/runtime.go

@@ -9,6 +9,7 @@ import (
 	"flare-ftso-indexer/internal/core"
 	"flare-ftso-indexer/internal/database"
 	"flare-ftso-indexer/internal/ready"
+	"math/big"
 	"time"
 
 	"github.com/flare-foundation/go-flare-common/pkg/logger"
@@ -22,6 +23,7 @@ func RunIndexer(
 	db *gorm.DB,
 	ethClient *chain.Client,
 	resolver *contracts.ContractResolver,
+	chainID *big.Int,
 ) error {
 	logger.Infof(
 		"Starting indexer in FSP mode: history_epochs=%d, fsp_tx_lookback_seconds=%d, collect_transactions=%d, collect_logs=%d",
@@ -49,9 +51,10 @@ func RunIndexer(
 		return errors.Wrap(err, "FSP startup backfill fatal error")
 	}
 
-	historyDropSeconds := historyDropHeuristicSeconds(cfg.Indexer.HistoryEpochs)
+	historyDropSeconds := historyDropHeuristicSeconds(chainID, cfg.Indexer.HistoryEpochs)
 	logger.Infof(
-		"Using FSP history drop: history_epochs=%d, derived retention=%ds (%.2f days)",
+		"Using FSP history drop: chain_id=%s, history_epochs=%d, derived retention=%ds (%.2f days)",
+		chainID,
 		cfg.Indexer.HistoryEpochs,
 		historyDropSeconds,
 		float64(historyDropSeconds)/(24*60*60),
@@ -89,12 +92,27 @@ func RunIndexer(
 	return nil
 }
 
-func historyDropHeuristicSeconds(historyEpochs uint64) uint64 {
-	// Over-estimation heuristic: history_epochs * 3.5 days + 14 days.
-	const (
-		baseRetentionSeconds     = uint64((14 * 24 * time.Hour) / time.Second)
-		retentionPerEpochSeconds = uint64((84 * time.Hour) / time.Second)
-	)
+// historyDropHeuristicSeconds derives the retention window used by history drop
+// from the number of FSP reward epochs that must remain indexable. It keeps three extra
+// reward epochs worth of history to cover the metadata event windows required by the
+// oldest indexed reward epoch + extra buffer for potentially extended epochs.
+func historyDropHeuristicSeconds(chainId *big.Int, historyEpochs uint64) uint64 {
+	return (historyEpochs + 4) * rewardEpochSecondsFor(chainId)
+}
 
-	return baseRetentionSeconds + historyEpochs*retentionPerEpochSeconds
+// rewardEpochSecondsByChain is the reward-epoch duration per network.
+// Mainnets run 3.5d epochs; testnets run 6h.
+var rewardEpochSecondsByChain = map[chain.ChainID]uint64{
+	chain.ChainIDFlare:    uint64((84 * time.Hour) / time.Second),
+	chain.ChainIDSongbird: uint64((84 * time.Hour) / time.Second),
+	chain.ChainIDCoston:   uint64((6 * time.Hour) / time.Second),
+	chain.ChainIDCoston2:  uint64((6 * time.Hour) / time.Second),
+}
+
+func rewardEpochSecondsFor(chainID *big.Int) uint64 {
+	chainIDInt := chain.ChainIDFromBigInt(chainID)
+	if v, ok := rewardEpochSecondsByChain[chainIDInt]; ok {
+		return v
+	}
+	return rewardEpochSecondsByChain[chain.ChainIDFlare]
 }