core/rawdb: change the mechanism to schedule freezer sync (#32135)

This pull request slightly improves the freezer fsync mechanism by scheduling 
the Sync operation based on the number of uncommitted items and original
time interval.

Originally, freezer.Sync was triggered every 30 seconds, which worked well during
active chain synchronization. However, once the initial state sync is complete, 
the fixed interval causes Sync to be scheduled too frequently.

To address this, the scheduling logic has been improved to consider both the time 
interval and the number of uncommitted items. This additional condition helps 
avoid unnecessary Sync operations when the chain is idle.

core/rawdb/freezer_batch.go

@@ -25,9 +25,16 @@ import (
 	"github.com/golang/snappy"
 )
 
+const (
 	// This is the maximum amount of data that will be buffered in memory
 	// for a single freezer table batch.
-const freezerBatchBufferLimit = 2 * 1024 * 1024
+	freezerBatchBufferLimit = 2 * 1024 * 1024
+
+	// freezerTableFlushThreshold defines the threshold for triggering a freezer
+	// table sync operation. If the number of accumulated uncommitted items exceeds
+	// this value, a sync will be scheduled.
+	freezerTableFlushThreshold = 512
+)
 
 // freezerBatch is a write operation of multiple items on a freezer.
 type freezerBatch struct {
@@ -201,6 +208,7 @@ func (batch *freezerTableBatch) commit() error {
 
 	// Update headBytes of table.
 	batch.t.headBytes += dataSize
+	items := batch.curItem - batch.t.items.Load()
 	batch.t.items.Store(batch.curItem)
 
 	// Update metrics.
@@ -208,7 +216,9 @@ func (batch *freezerTableBatch) commit() error {
 	batch.t.writeMeter.Mark(dataSize + indexSize)
 
 	// Periodically sync the table, todo (rjl493456442) make it configurable?
-	if time.Since(batch.t.lastSync) > 30*time.Second {
+	batch.t.uncommitted += items
+	if batch.t.uncommitted > freezerTableFlushThreshold && time.Since(batch.t.lastSync) > 30*time.Second {
+		batch.t.uncommitted = 0
 		batch.t.lastSync = time.Now()
 		return batch.t.Sync()
 	}

core/rawdb/freezer_table.go

@@ -113,6 +113,7 @@ type freezerTable struct {
 	tailId uint32              // number of the earliest file
 
 	metadata    *freezerTableMeta // metadata of the table
+	uncommitted uint64            // Count of items written without flushing to file
 	lastSync    time.Time         // Timestamp when the last sync was performed
 
 	headBytes  int64          // Number of bytes written to the head file