diff --git a/Dockerfile b/Dockerfile
index a938575..bb3835b 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -7,4 +7,8 @@ COPY ./target/scala-2.13/WeatherTool-assembly-0.1.1-SNAPSHOT.jar app.jar
 
 VOLUME /app/data
 
-CMD ["java", "-jar", "app.jar"]
\ No newline at end of file
+
+# flags setting heap to 256mb and max 384mb, plus g1 garbage collector
+# CMD ["java", "-Xms256m", "-Xmx384m", "-XX:+UseG1GC", "-jar", "app.jar"]
+# CMD ["java", "-jar", "app.jar"]
+CMD ["java", "-Xms512m", "-Xmx600m", "-XX:+UseG1GC", "-XX:MaxGCPauseMillis=200", "-jar", "app.jar"]
\ No newline at end of file
diff --git a/fly.toml b/fly.toml
index 3beb42e..d21e977 100644
--- a/fly.toml
+++ b/fly.toml
@@ -18,7 +18,7 @@ primary_region = "waw"
   size_gb = 10
 
 [[vm]]
-  memory = 512
+  memory = 1024
   cpu_kind = 'shared'
   cpus = 1
 
diff --git a/src/main/scala/data/DataService.scala b/src/main/scala/data/DataService.scala
index 0738093..e808163 100644
--- a/src/main/scala/data/DataService.scala
+++ b/src/main/scala/data/DataService.scala
@@ -64,29 +64,40 @@ class DataService(log: Logger[IO]) {
   def getAllFileStructure(): IO[List[Grib]] = {
     for {
       fileList <- getFileList()
-      allStructure <- fileList.parTraverseN(4)(getGribStucture) // limit concurrency to 4
+      allStructure <- fileList.parTraverseN(4)(getGribStucture) // limit concurrency
     } yield allStructure.flatten
   }
 
-//  private val blockingEC = ExecutionContext.fromExecutorService(
-//    Executors.newFixedThreadPool(4) // limit concurrency to 4
-//  )
-//
-//  private val semaphore = Semaphore[IO](4).unsafeRunSync()
+  private val semaphore = Semaphore[IO](4).unsafeRunSync()
+
+  private val blockingEC = ExecutionContext.fromExecutorService(
+    Executors.newFixedThreadPool(4) // limit concurrency
+  )
 
   def getBinaryChunk(offset: Int, length: Int, fileName: String): IO[Array[Byte]] = {
     val fileResource = Resource.make(
       IO.blocking(new RandomAccessFile(s"$GRIB_FOLDER/$fileName", "r"))
     )(file => IO.blocking(file.close()))
 
-    fileResource.use { file =>
-      IO.blocking {
-        val buffer = new Array[Byte](length)
-        file.seek(offset)
-        file.readFully(buffer)
-        buffer
-      }
+    val logMemory = IO {
+      val runtime = Runtime.getRuntime
+      val usedMemoryMB = (runtime.totalMemory - runtime.freeMemory) / 1024 / 1024
+      val maxMemoryMB = runtime.maxMemory / 1024 / 1024
+      println(s"Memory usage before reading $fileName: $usedMemoryMB MB / $maxMemoryMB MB max")
     }
+
+    for {
+      _ <- logMemory
+      result <- fileResource.use { file =>
+        IO.blocking {
+          val buffer = new Array[Byte](length)
+          file.seek(offset)
+          file.readFully(buffer)
+          buffer
+        }.evalOn(blockingEC)
+      }
+      _ <- IO { System.gc() }
+    } yield result
   }
 
   def getForecasts(): IO[List[(ZonedDateTime, ZonedDateTime)]] = {
diff --git a/web/src/harmonie/ReferenceTimes.tsx b/web/src/harmonie/ReferenceTimes.tsx
index f06f4a9..b897b5e 100644
--- a/web/src/harmonie/ReferenceTimes.tsx
+++ b/web/src/harmonie/ReferenceTimes.tsx
@@ -6,7 +6,7 @@ import { drawGrib } from './draw/drawGrib'
 import { CROP_BOUNDS } from './DrawView'
 
 import styles from './harmonie.module.css'
-import { handleProgressivePromises } from '../helpers/progressivePromises'
+import { processPromisesInBatches } from '../helpers/progressivePromises'
 
 const METEO_PARAMS: [string, MeteoParam][] = [
     ['temperature', { discipline: 0, category: 0, product: 0, levelType: -1, levelValue: -1, subType: 'now' }],
@@ -62,7 +62,7 @@ export const ReferenceTimes: Component<{
             .map((grib): [string, undefined] => [grib.time.forecastTime, undefined])
             .sort((a, b) => a[0] > b[0] ? 1 : -1)
         setImgList(emptyImgList)
-        const promiseList = forecastList.map(async (grib): Promise<[string, ImageBitmap]> => {
+        const promiseFnsList = forecastList.map((grib): () => Promise<[string, ImageBitmap]> => async () => {
             const canvas = document.createElement('canvas')
             const [messages, buffers, bitmasks] = await fetchGribBinaries(grib, getGribList())
             drawGrib(canvas, messages, buffers, bitmasks, cropBounds, contour, isInterpolated)
@@ -72,8 +72,8 @@ export const ReferenceTimes: Component<{
             return [grib.time.forecastTime, img]
         })
 
-        handleProgressivePromises(
-            promiseList,
+        processPromisesInBatches(
+            promiseFnsList,
             ([forecastDate, img]) => {
                 const udpdatedImgList = [...getImgList()]
                 const idx = udpdatedImgList.findIndex(([d]) => forecastDate === d)
diff --git a/web/src/helpers/progressivePromises.ts b/web/src/helpers/progressivePromises.ts
index 3aee7cc..1572928 100644
--- a/web/src/helpers/progressivePromises.ts
+++ b/web/src/helpers/progressivePromises.ts
@@ -1,10 +1,10 @@
-export async function handleProgressivePromises<T>(
-    promises: Promise<T>[],
+async function processPromises<T>(
+    promiseFns: (() => Promise<T>)[],
     onProgress: (result: T) => void,
 ): Promise<(T | undefined)[]> {
-    const allPromises = promises.map(async promise => {
+    const allPromises = promiseFns.map(async promise => {
         try {
-            const result = await promise;
+            const result = await promise();
             onProgress(result)
             return result
         } catch (error) {
@@ -17,3 +17,20 @@ export async function handleProgressivePromises<T>(
         result.status === 'fulfilled' ? result.value : undefined
     )
 }
+
+export async function processPromisesInBatches<T>(
+    promiseFns: (() => Promise<T>)[],
+    onProgress: (result: T) => void,
+    batchSize = 3,
+): Promise<(T | undefined)[]> {
+    const results = []
+    while(await promiseFns.length > 0) {
+        const size = Math.min(batchSize, promiseFns.length)
+        const batchPromises = promiseFns.splice(0, size)
+        console.log('process:', batchPromises.length)
+        const batchResults = await processPromises(batchPromises, onProgress)
+        results.push(...batchResults)
+    }
+
+    return results
+}