diff --git a/documentation/adrs/0016-use-slack-to-inform-user-about-important-system-events.md b/documentation/adrs/0016-use-slack-to-inform-user-about-important-system-events.md
new file mode 100644
index 0000000..83022dc
--- /dev/null
+++ b/documentation/adrs/0016-use-slack-to-inform-user-about-important-system-events.md
@@ -0,0 +1,22 @@
+# 16. use Slack to inform user about important system events
+
+Date: 2024-02-02
+
+## Status
+
+Accepted
+
+## Context
+
+Requirement F-004 requires the owners of the system to be informed about important system events.
+
+## Decision
+
+Such important events are "system startup" and "acquisition of usage and repository data".
+These shall be sent to a Slack channel to notify the owners.
+
+## Consequences
+
+- Slack app to be created
+- [Slack API](https://pkg.go.dev/github.com/slack-go/slack@v0.12.3#section-readme) to be used
+- Slack OAuth Token to be set at fly.io
\ No newline at end of file
diff --git a/documentation/arc42/chapters/01_introduction_and_goals.adoc b/documentation/arc42/chapters/01_introduction_and_goals.adoc
index 8c42f7f..1aefea5 100644
--- a/documentation/arc42/chapters/01_introduction_and_goals.adoc
+++ b/documentation/arc42/chapters/01_introduction_and_goals.adoc
@@ -17,11 +17,22 @@ ifndef::imagesdir[:imagesdir: ../../images]
 
 === Requirements Overview
 
+[glossary]
+F-001:: publish current usage statistics of arc42 websites
 
+F-002:: publish current repository statistics (like issues, bugs) of arc42 websites
+
+F-003:: store important results and events persistently for future reference
+
+F-004:: inform owners of important system events
 
 === Quality Goals
 
-* Environmental friendly: Reduce computing resources used as much as possible.
+[glossary]
+
+Q-001:: Environmental friendly: Reduce computing resources used as much as possible.
+
+Q-002:: Available: statics are available via the website 24x7. Short periods (hours) of downtime can be allowed, in such cases cached or dated results shall be displayed.
 
 
 === Stakeholders
diff --git a/documentation/images/06-system-startup.puml b/documentation/images/06-system-startup.puml
index 96ada4e..e10ba4e 100644
--- a/documentation/images/06-system-startup.puml
+++ b/documentation/images/06-system-startup.puml
@@ -2,36 +2,29 @@
 'https://plantuml.com/activity-diagram-beta
 
 start
-:ClickServlet.handleRequest();
-:new page;
-if (Page.onSecurityCheck) then (true)
-  :Page.onInit();
-  if (isForward?) then (no)
-    :Process controls;
-    if (continue processing?) then (no)
-      stop
-    endif
-
-    if (isPost?) then (yes)
-      :Page.onPost();
-    else (no)
-      :Page.onGet();
-    endif
-    :Page.onRender();
-  endif
-else (false)
-endif
 
-if (do redirect?) then (yes)
-  :redirect process;
-else
-  if (do forward?) then (yes)
-    :Forward request;
-  else (no)
-    :Render page template;
-  endif
-endif
+:init logger, db, cache;
+
+:siteStats = loadStats();
+
+:cache siteStats, expiry 10min;
+
+:repoStats = loadRepoStats();
+:cache repoStats, expiry 1min;
 
-stop
+group API Server Process
+:apiGateway.StartAPIServer();
+
+detach
+
+:wait for http request;
+
+if (External Event occurs) then (yes)
+    :execute method B;
+else (no)
+    :skip method B;
+endif
 
+end group
+:finalize process;
 @enduml
diff --git a/documentation/images/slack-app/slack-status-gopher-logo.pptx b/documentation/images/slack-app/slack-status-gopher-logo.pptx
new file mode 100644
index 0000000..d8a3c9d
Binary files /dev/null and b/documentation/images/slack-app/slack-status-gopher-logo.pptx differ
diff --git a/documentation/images/slack-app/slack-status-gopher.png b/documentation/images/slack-app/slack-status-gopher.png
new file mode 100644
index 0000000..189eb1d
Binary files /dev/null and b/documentation/images/slack-app/slack-status-gopher.png differ
diff --git a/go-app/internal/api/apiGateway.go b/go-app/internal/api/apiGateway.go
index b5182b9..5339508 100644
--- a/go-app/internal/api/apiGateway.go
+++ b/go-app/internal/api/apiGateway.go
@@ -70,13 +70,12 @@ func statsHTMLTableHandler(w http.ResponseWriter, r *http.Request) {
 		domain.ArcStats.FlyRegion, domain.ArcStats.WhereDoesItRun = fly.RegionAndLocation()
 
 		// 4. store request params in database
-		// TODO: make this async
 		// TODO: include real IP address
-		database.SaveInvocationParams(r.Host, r.RequestURI)
+		go database.SaveInvocationParams(r.Host, r.RequestURI)
 
-		// 4b: inform owner via Slack
+		// 4b: inform the owner via Slack
 		msg := fmt.Sprintf("Loaded arc42 statistics in %sms on %s", domain.ArcStats.HowLongDidItTake, time.Now().Format("02 Jan 15:04"))
-		slack.SendSlackMessage(msg)
+		go slack.SendSlackMessage(msg)
 
 		// 5. finally, render the template
 		executeTemplate(w, filepath.Join(TemplatesDir, HtmlTableTmpl), domain.ArcStats)
diff --git a/go-app/main.go b/go-app/main.go
index a95cefb..c9e6ae4 100644
--- a/go-app/main.go
+++ b/go-app/main.go
@@ -13,7 +13,7 @@ import (
 	"time"
 )
 
-const appVersion = "0.5.6"
+const appVersion = "0.5.7"
 
 // version history
 // 0.5.x rate limit: limit amount of queries to external APIs
@@ -22,6 +22,7 @@ const appVersion = "0.5.6"
 // 		 0.5.4: start with empty table on homepage
 // 		 0.5.5: caching with zcache
 //		 0.5.6: send slack message for important system events, starting with data acquisition
+//       0.5.7: performance optimization, initial database insert and Slack message now async
 // 0.4.7 replace most inline styles by css
 // 0.4.6 sortable table (a: initial, b...e: fix layout issues), f: fix #94
 // 0.4.5 fix missing separators in large numbers