From 747b4cf26c35f66b06b45416b8dd61d09b652e97 Mon Sep 17 00:00:00 2001
From: Agniva De Sarker <agnivade@yahoo.co.in>
Date: Thu, 15 Jun 2023 21:08:14 +0530
Subject: [PATCH] MM-53058: Move cache layer out of timer layer (#23660)

Having cache layer as part of the store call
Prometheus metrics can be somewhat misleading
because cache-backed methods can have very high
volume and yet not cause any load on the DB at all.

However, if the admin is not aware which calls
are cache-backed and which are not, then
it can be hard to understand why a store call
of high volume isn't causing any stress on the DB at all.

Therefore, for simplicity we reorder the layers
such that cache layer is handled outside the timer layer.

We already have cache related metrics like hit/miss
which can be used to monitor cache usage.

https://mattermost.atlassian.net/browse/MM-53058

```release-note
NONE
```

Co-authored-by: Mattermost Build <build@mattermost.com>
---
 server/channels/app/platform/service.go | 37 +++++++++++++++----------
 1 file changed, 22 insertions(+), 15 deletions(-)

diff --git a/server/channels/app/platform/service.go b/server/channels/app/platform/service.go
index ab81f43b29..11fbfd2cac 100644
--- a/server/channels/app/platform/service.go
+++ b/server/channels/app/platform/service.go
@@ -193,20 +193,20 @@ func New(sc ServiceConfig, options ...Option) (*PlatformService, error) {
 	// Depends on Step 0 (config), 1 (cacheProvider), 3 (search engine), 5 (metrics) and cluster.
 	if ps.newStore == nil {
 		ps.newStore = func() (store.Store, error) {
+			// The layer cake is as follows: (From bottom to top)
+			// SQL layer
+			// |
+			// Retry layer
+			// |
+			// Search layer
+			// |
+			// Timer layer
+			// |
+			// Cache layer
 			ps.sqlStore = sqlstore.New(ps.Config().SqlSettings, ps.metricsIFace)
 
-			lcl, err2 := localcachelayer.NewLocalCacheLayer(
-				retrylayer.New(ps.sqlStore),
-				ps.metricsIFace,
-				ps.clusterIFace,
-				ps.cacheProvider,
-			)
-			if err2 != nil {
-				return nil, fmt.Errorf("cannot create local cache layer: %w", err2)
-			}
-
 			searchStore := searchlayer.NewSearchLayer(
-				lcl,
+				retrylayer.New(ps.sqlStore),
 				ps.SearchEngine,
 				ps.Config(),
 			)
@@ -215,16 +215,23 @@ func New(sc ServiceConfig, options ...Option) (*PlatformService, error) {
 				searchStore.UpdateConfig(cfg)
 			})
 
+			lcl, err2 := localcachelayer.NewLocalCacheLayer(
+				timerlayer.New(searchStore, ps.metricsIFace),
+				ps.metricsIFace,
+				ps.clusterIFace,
+				ps.cacheProvider,
+			)
+			if err2 != nil {
+				return nil, fmt.Errorf("cannot create local cache layer: %w", err2)
+			}
+
 			license := ps.License()
 			ps.sqlStore.UpdateLicense(license)
 			ps.AddLicenseListener(func(oldLicense, newLicense *model.License) {
 				ps.sqlStore.UpdateLicense(newLicense)
 			})
 
-			return timerlayer.New(
-				searchStore,
-				ps.metricsIFace,
-			), nil
+			return lcl, nil
 		}
 	}