[#1346] Troubleshooting synchronization

- changelog update
- the sync time has been reduced by ~33%. The progress reporting frequency has been lowered down 5-times
- this is just first step and a quick improvement before we introduce advanced solution, covered in #1353

[#1346] Troubleshooting synchronization (#1354)

- typo fixed

CHANGELOG.md

@@ -4,6 +4,13 @@ All notable changes to this library will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this library adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+# [Unreleased]
+
+## Changed
+
+### [#1346] Troubleshooting synchronization
+We focused on performance of the synchronization and found out a root cause in progress reporting. Simple change reduced the synchronization significantly by reporting less frequently. This affect the UX a bit because the % of the sync is updated only every 500 scanned blocks instead of every 100. Proper solution is going to be handled in #1353.
+
 # 2.0.5 - 2023-12-15
 
 ## Added

Sources/ZcashLightClientKit/Block/Actions/ScanAction.swift

@@ -8,11 +8,16 @@
 import Foundation
 
 final class ScanAction {
+    enum Constants {
+        static let reportDelay = 5
+    }
+    
     let configProvider: CompactBlockProcessor.ConfigProvider
     let blockScanner: BlockScanner
     let rustBackend: ZcashRustBackendWelding
     let latestBlocksDataProvider: LatestBlocksDataProvider
     let logger: Logger
+    var progressReportReducer = Constants.reportDelay
 
     init(container: DIContainer, configProvider: CompactBlockProcessor.ConfigProvider) {
         self.configProvider = configProvider
@@ -55,20 +60,29 @@ extension ScanAction: Action {
         do {
             try await blockScanner.scanBlocks(at: batchRange) { [weak self] lastScannedHeight, increment in
                 let processedHeight = await context.processedHeight
-                let incrementedprocessedHeight = processedHeight + BlockHeight(increment)
-                await context.update(processedHeight: incrementedprocessedHeight)
+                let incrementedProcessedHeight = processedHeight + BlockHeight(increment)
+                await context.update(processedHeight: incrementedProcessedHeight)
                 await self?.latestBlocksDataProvider.updateScannedData()
                 
-                // report scan progress only if it's available
-                if let scanProgress = try? await self?.rustBackend.getScanProgress() {
-                    let progress = try scanProgress.progress()
-                    self?.logger.debug("progress: \(progress)")
-                    await didUpdate(.syncProgress(progress))
-                }
-                
                 // ScanAction is controlled locally so it must report back the updated scanned height
                 await context.update(lastScannedHeight: lastScannedHeight)
             }
+            
+            // This is a simple change that reduced the synchronization time significantly while affecting the UX only a bit.
+            // The frequency of UI progress update is lowered x5 times.
+            // Proper solution is handled in
+            // TODO: [#1353] Advanced progress reporting, https://github.com/Electric-Coin-Company/zcash-swift-wallet-sdk/issues/1353
+            if progressReportReducer == 0 {
+                // report scan progress only if it's available
+                if let scanProgress = try? await rustBackend.getScanProgress() {
+                    let progress = try scanProgress.progress()
+                    logger.debug("progress: \(progress)")
+                    await didUpdate(.syncProgress(progress))
+                }
+                progressReportReducer = Constants.reportDelay
+            } else {
+                progressReportReducer -= 1
+            }
         } catch ZcashError.rustScanBlocks(let errorMsg) {
             if isContinuityError(errorMsg) {
                 await context.update(requestedRewindHeight: batchRange.lowerBound - 10)
@@ -84,7 +98,9 @@ extension ScanAction: Action {
         return await update(context: context)
     }
 
-    func stop() async { }
+    func stop() async { 
+        progressReportReducer = Constants.reportDelay
+    }
 }
 
 private extension ScanAction {