services/horizon: Make reaping batch sizes configurable via --history-retention-reap-count.

services/horizon/internal/app.go

@@ -506,7 +506,11 @@ func (a *App) init() error {
 	initSubmissionSystem(a)
 
 	// reaper
-	a.reaper = reap.New(a.config.HistoryRetentionCount, a.HorizonSession(), a.ledgerState)
+	a.reaper = reap.New(
+		a.config.HistoryRetentionCount,
+		a.config.HistoryRetentionReapCount,
+		a.HorizonSession(),
+		a.ledgerState)
 
 	// go metrics
 	initGoMetrics(a)

services/horizon/internal/config.go

@@ -75,6 +75,12 @@ type Config struct {
 	// determining a "retention duration", each ledger roughly corresponds to 10
 	// seconds of real time.
 	HistoryRetentionCount uint
+	// HistoryRetentionReapCount is the number of ledgers worth of history data
+	// to remove per second from the Horizon database. It is intended to allow
+	// control over the amount of CPU and database load caused by reaping,
+	// especially if enabling reaping for the first time or in times of
+	// increased ledger load.
+	HistoryRetentionReapCount uint
 	// StaleThreshold represents the number of ledgers a history database may be
 	// out-of-date by before horizon begins to respond with an error to history
 	// requests.

services/horizon/internal/db2/history/reap_test.go

@@ -17,7 +17,7 @@ func TestReapLookupTables(t *testing.T) {
 
 	db := tt.HorizonSession()
 
-	sys := reap.New(0, db, ledgerState)
+	sys := reap.New(0, 0, db, ledgerState)
 
 	var (
 		prevLedgers, curLedgers                     int

services/horizon/internal/flags.go

@@ -654,9 +654,23 @@ func Flags() (*Config, support.ConfigOptions) {
 			ConfigKey:      &config.HistoryRetentionCount,
 			OptType:        types.Uint,
 			FlagDefault:    uint(0),
-			Usage:          "the minimum number of ledgers to maintain within horizon's history tables.  0 signifies an unlimited number of ledgers will be retained",
+			Usage:          "the minimum number of ledgers to maintain within Horizon's history tables (0 = retain an unlimited number of ledgers)",
 			UsedInCommands: IngestionCommands,
 		},
+		&support.ConfigOption{
+			Name:           "history-retention-reap-count",
+			ConfigKey:      &config.HistoryRetentionReapCount,
+			OptType:        types.Uint,
+			FlagDefault:    uint(50_000),
+			Usage:          "the batch size (in ledgers) to remove per reap from the Horizon database",
+			UsedInCommands: IngestionCommands,
+			CustomSetValue: func(opt *support.ConfigOption) error {
+				if val := viper.GetUint(opt.Name); val <= 0 || val > 500_000 {
+					return fmt.Errorf("flag --history-retention-reap-count must be in range [1, 500,000]")
+				}
+				return nil
+			},
+		},
 		&support.ConfigOption{
 			Name:           "history-stale-threshold",
 			ConfigKey:      &config.StaleThreshold,

services/horizon/internal/reap/main.go

@@ -16,19 +16,22 @@ import (
 type System struct {
 	HistoryQ       *history.Q
 	RetentionCount uint
-	ledgerState    *ledger.State
-	ctx            context.Context
-	cancel         context.CancelFunc
+	RetentionBatch uint
+
+	ledgerState *ledger.State
+	ctx         context.Context
+	cancel      context.CancelFunc
 }
 
 // New initializes the reaper, causing it to begin polling the stellar-core
 // database for now ledgers and ingesting data into the horizon database.
-func New(retention uint, dbSession db.SessionInterface, ledgerState *ledger.State) *System {
+func New(retention, retentionBatchSize uint, dbSession db.SessionInterface, ledgerState *ledger.State) *System {
 	ctx, cancel := context.WithCancel(context.Background())
 
 	r := &System{
 		HistoryQ:       &history.Q{dbSession.Clone()},
 		RetentionCount: retention,
+		RetentionBatch: retentionBatchSize,
 		ledgerState:    ledgerState,
 		ctx:            ctx,
 		cancel:         cancel,

services/horizon/internal/reap/system.go

@@ -2,6 +2,7 @@ package reap
 
 import (
 	"context"
+	"fmt"
 	"time"
 
 	herrors "github.com/stellar/go/services/horizon/internal/errors"
@@ -70,25 +71,31 @@ func (r *System) runOnce(ctx context.Context) {
 	}
 }
 
-// Work backwards in 100k ledger blocks to prevent using all the CPU.
+// Work backwards in 50k (by default, otherwise configurable via the CLI) ledger
+// blocks to prevent using all the CPU.
 //
-// This runs every hour, so we need to make sure it doesn't
-// run for longer than an hour.
+// This runs every hour, so we need to make sure it doesn't run for longer than
+// an hour.
 //
-// Current ledger at 2021-08-12 is 36,827,497, so 100k means 368 batches. At 1
-// batch/second, that seems like a reasonable balance between running well
-// under an hour, and slowing it down enough to leave some CPU for other
-// processes.
-var batchSize = int32(100_000)
+// Current ledger at 2024-04-04s is 51,092,283, so 50k means 1021 batches. At 1
+// batch/second, that seems like a reasonable balance between running under an
+// hour, and slowing it down enough to leave some CPU for other processes.
 var sleep = 1 * time.Second
 
 func (r *System) clearBefore(ctx context.Context, startSeq, endSeq int32) error {
+	batchSize := int32(r.RetentionBatch)
+	if batchSize <= 0 {
+		return fmt.Errorf("invalid batch size for reaping (%d)", batchSize)
+	}
+
 	for batchEndSeq := endSeq - 1; batchEndSeq >= startSeq; batchEndSeq -= batchSize {
 		batchStartSeq := batchEndSeq - batchSize
 		if batchStartSeq < startSeq {
 			batchStartSeq = startSeq
 		}
-		log.WithField("start_ledger", batchStartSeq).WithField("end_ledger", batchEndSeq).Info("reaper: clearing")
+		log.WithField("start_ledger", batchStartSeq).
+			WithField("end_ledger", batchEndSeq).
+			Info("reaper: clearing")
 
 		batchStart, batchEnd, err := toid.LedgerRangeInclusive(batchStartSeq, batchEndSeq)
 		if err != nil {

services/horizon/internal/reap/system_test.go

@@ -15,7 +15,7 @@ func TestDeleteUnretainedHistory(t *testing.T) {
 
 	db := tt.HorizonSession()
 
-	sys := New(0, db, ledgerState)
+	sys := New(0, 50_000, db, ledgerState)
 
 	// Disable sleeps for this.
 	sleep = 0