From 1831c731a3441baf1b2d26eb3370dd8c9017eb39 Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@victoriametrics.com>
Date: Thu, 23 Nov 2023 20:39:40 +0200
Subject: [PATCH] app/vmagent/remotewrite: do not drop persistent queues when
 -remoteWrite.multitenantURL is set

It is unsafe to drop persistent queues when -remoteWrite.multitenantURL command-line flag is set,
since these queues are created on demand when a new sample for the given tenant is pushed
to the remote storage.

This addresses https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5357
The issue has been appeared in the commit f3a51e8b1d03f498aca84b77656d20e12417f282
when implementing https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4014
---
 app/vmagent/remotewrite/remotewrite.go | 64 +++++++++++++++-----------
 docs/CHANGELOG.md                      |  1 +
 2 files changed, 38 insertions(+), 27 deletions(-)

diff --git a/app/vmagent/remotewrite/remotewrite.go b/app/vmagent/remotewrite/remotewrite.go
index a676fdb88..d9264e3ba 100644
--- a/app/vmagent/remotewrite/remotewrite.go
+++ b/app/vmagent/remotewrite/remotewrite.go
@@ -183,6 +183,7 @@ func Init() {
 	if len(*remoteWriteURLs) > 0 {
 		rwctxsDefault = newRemoteWriteCtxs(nil, *remoteWriteURLs)
 	}
+	dropDanglingQueues()
 
 	// Start config reloader.
 	configReloaderWG.Add(1)
@@ -200,6 +201,42 @@ func Init() {
 	}()
 }
 
+func dropDanglingQueues() {
+	if *keepDanglingQueues {
+		return
+	}
+	if len(*remoteWriteMultitenantURLs) > 0 {
+		// Do not drop dangling queues for *remoteWriteMultitenantURLs, since it is impossible to determine
+		// unused queues for multitenant urls - they are created on demand when new sample for the given
+		// tenant is pushed to remote storage.
+		return
+	}
+	// Remove dangling persistent queues, if any.
+	// This is required for the case when the number of queues has been changed or URL have been changed.
+	// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4014
+	//
+	existingQueues := make(map[string]struct{}, len(rwctxsDefault))
+	for _, rwctx := range rwctxsDefault {
+		existingQueues[rwctx.fq.Dirname()] = struct{}{}
+	}
+
+	queuesDir := filepath.Join(*tmpDataPath, persistentQueueDirname)
+	files := fs.MustReadDir(queuesDir)
+	removed := 0
+	for _, f := range files {
+		dirname := f.Name()
+		if _, ok := existingQueues[dirname]; !ok {
+			logger.Infof("removing dangling queue %q", dirname)
+			fullPath := filepath.Join(queuesDir, dirname)
+			fs.MustRemoveAll(fullPath)
+			removed++
+		}
+	}
+	if removed > 0 {
+		logger.Infof("removed %d dangling queues from %q, active queues: %d", removed, *tmpDataPath, len(rwctxsDefault))
+	}
+}
+
 func reloadRelabelConfigs() {
 	relabelConfigReloads.Inc()
 	logger.Infof("reloading relabel configs pointed by -remoteWrite.relabelConfig and -remoteWrite.urlRelabelConfig")
@@ -273,33 +310,6 @@ func newRemoteWriteCtxs(at *auth.Token, urls []string) []*remoteWriteCtx {
 		}
 		rwctxs[i] = newRemoteWriteCtx(i, remoteWriteURL, maxInmemoryBlocks, sanitizedURL)
 	}
-
-	if !*keepDanglingQueues {
-		// Remove dangling queues, if any.
-		// This is required for the case when the number of queues has been changed or URL have been changed.
-		// See: https://github.com/VictoriaMetrics/VictoriaMetrics/issues/4014
-		existingQueues := make(map[string]struct{}, len(rwctxs))
-		for _, rwctx := range rwctxs {
-			existingQueues[rwctx.fq.Dirname()] = struct{}{}
-		}
-
-		queuesDir := filepath.Join(*tmpDataPath, persistentQueueDirname)
-		files := fs.MustReadDir(queuesDir)
-		removed := 0
-		for _, f := range files {
-			dirname := f.Name()
-			if _, ok := existingQueues[dirname]; !ok {
-				logger.Infof("removing dangling queue %q", dirname)
-				fullPath := filepath.Join(queuesDir, dirname)
-				fs.MustRemoveAll(fullPath)
-				removed++
-			}
-		}
-		if removed > 0 {
-			logger.Infof("removed %d dangling queues from %q, active queues: %d", removed, *tmpDataPath, len(rwctxs))
-		}
-	}
-
 	return rwctxs
 }
 
diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index c84351a28..5e1e926e2 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -28,6 +28,7 @@ The sandbox cluster installation is running under the constant load generated by
 
 ## tip
 
+* BUGFIX: [vmagent](https://docs.victoriametrics.com/vmagent.html): prevent from `FATAL: cannot flush metainfo` panic when [`-remoteWrite.multitenantURL`](https://docs.victoriametrics.com/vmagent.html#multitenancy) command-line flag is set. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5357).
 * BUGFIX: [vmagent](https://docs.victoriametrics.com/vmagent.html): properly decode zstd-encoded data blocks received via [VictoriaMetrics remote_write protocol](https://docs.victoriametrics.com/vmagent.html#victoriametrics-remote-write-protocol). See [this issue comment](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5301#issuecomment-1815871992).
 
 ## [v1.95.1](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v1.95.1)