diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 9b08c5b55..1d259ede2 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -23,6 +23,8 @@ The following tip changes can be tested by building VictoriaMetrics components f
 * FEATURE: [vmalert enterprise](https://docs.victoriametrics.com/vmalert.html): add ability to read alerting and recording rules from S3, GCS or S3-compatible object storage. See [these docs](https://docs.victoriametrics.com/vmalert.html#reading-rules-from-object-storage).
 * FEATURE: [MetricsQL](https://docs.victoriametrics.com/MetricsQL.html): add `mad_over_time(m[d])` function for calculating the [median absolute deviation](https://en.wikipedia.org/wiki/Median_absolute_deviation) over raw samples on the lookbehind window `d`. See [this feature request](https://github.com/prometheus/prometheus/issues/5514).
 
+* BUGFIX: prevent from possible data ingestion slowdown and query performance slowdown during [background merges of big parts](https://docs.victoriametrics.com/#storage) on systems with small number of CPU cores (1 or 2 CPU cores). The issue has been introduced in [v1.85.0](https://docs.victoriametrics.com/CHANGELOG.html#v1850) when implementing [this feature](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3337). See also [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3790).
+
 ## [v1.87.1](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v1.87.1)
 
 Released at 2023-02-09
diff --git a/lib/mergeset/table.go b/lib/mergeset/table.go
index ef403174e..9ca34650b 100644
--- a/lib/mergeset/table.go
+++ b/lib/mergeset/table.go
@@ -788,7 +788,18 @@ func (tb *Table) notifyBackgroundMergers() bool {
 	}
 }
 
-var flushConcurrencyCh = make(chan struct{}, cgroup.AvailableCPUs())
+var flushConcurrencyLimit = func() int {
+	n := cgroup.AvailableCPUs()
+	if n < 2 {
+		// Allow at least 2 concurrent flushers on systems with a single CPU core
+		// in order to guarantee that in-memory data flushes and background merges can be continued
+		// when a single flusher is busy with the long merge.
+		n = 2
+	}
+	return n
+}()
+
+var flushConcurrencyCh = make(chan struct{}, flushConcurrencyLimit)
 
 func needAssistedMerge(pws []*partWrapper, maxParts int) bool {
 	if len(pws) < maxParts {
diff --git a/lib/storage/partition.go b/lib/storage/partition.go
index cbcaf295d..15b9e1a0e 100644
--- a/lib/storage/partition.go
+++ b/lib/storage/partition.go
@@ -615,7 +615,19 @@ func (pt *partition) notifyBackgroundMergers() bool {
 	}
 }
 
-var flushConcurrencyCh = make(chan struct{}, cgroup.AvailableCPUs())
+var flushConcurrencyLimit = func() int {
+	n := cgroup.AvailableCPUs()
+	if n < 3 {
+		// Allow at least 3 concurrent flushers on systems with a single CPU core
+		// in order to guarantee that in-memory data flushes and background merges can be continued
+		// when a single flusher is busy with the long merge of big parts,
+		// while another flusher is busy with the long merge of small parts.
+		n = 3
+	}
+	return n
+}()
+
+var flushConcurrencyCh = make(chan struct{}, flushConcurrencyLimit)
 
 func needAssistedMerge(pws []*partWrapper, maxParts int) bool {
 	if len(pws) < maxParts {
@@ -1007,7 +1019,7 @@ func hasActiveMerges(pws []*partWrapper) bool {
 	return false
 }
 
-var mergeWorkersLimitCh = make(chan struct{}, getDefaultMergeConcurrency(16))
+var mergeWorkersLimitCh = make(chan struct{}, adjustMergeWorkersLimit(getDefaultMergeConcurrency(16)))
 
 var bigMergeWorkersLimitCh = make(chan struct{}, getDefaultMergeConcurrency(4))
 
@@ -1038,9 +1050,20 @@ func SetMergeWorkersCount(n int) {
 		// Do nothing
 		return
 	}
+	n = adjustMergeWorkersLimit(n)
 	mergeWorkersLimitCh = make(chan struct{}, n)
 }
 
+func adjustMergeWorkersLimit(n int) int {
+	if n < 2 {
+		// Allow at least 2 merge workers on systems with a single CPU core
+		// in order to guarantee that background merges can be continued
+		// when a single worker is busy with the long merge of big parts.
+		return 2
+	}
+	return n
+}
+
 func (pt *partition) startMergeWorkers() {
 	// Start a merge worker per available CPU core.
 	// The actual number of concurrent merges is limited inside mergeWorker() below.