fix(tsdb): survive low disk space

pkg/tsdb/disk_guard_test.go

@@ -0,0 +1,124 @@
+package tsdb
+
+import (
+	"path/filepath"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/storage"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+type testReadOnlyChecker struct {
+	value atomic.Bool
+}
+
+func (c *testReadOnlyChecker) IsReadOnly() bool {
+	return c.value.Load()
+}
+
+func newDiskGuardTestDB(t *testing.T) *TSDB {
+	t.Helper()
+	db, err := Open(&Config{
+		DataPath:           filepath.Join(t.TempDir(), "tsdb"),
+		RetentionDays:      1,
+		MinFreeDiskSpaceGB: 1,
+		DedupInterval:      time.Second,
+	})
+	require.NoError(t, err)
+	t.Cleanup(func() { require.NoError(t, db.Close()) })
+	return db
+}
+
+func bufferedRows(w *bufferedWriter) int {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	return len(w.buffer)
+}
+
+func TestReadOnlyStorageDropsWritesAndKeepsQueriesAvailable(t *testing.T) {
+	db := newDiskGuardTestDB(t)
+	checker := &testReadOnlyChecker{}
+	db.readOnly = checker
+	originalAddRows := db.addRowsFn
+	var addRowsCalls atomic.Int32
+	db.addRowsFn = func(rows []storage.MetricRow, precisionBits uint8) {
+		addRowsCalls.Add(1)
+		originalAddRows(rows, precisionBits)
+	}
+
+	firstTimestamp := time.Now().Add(-time.Minute)
+	require.NoError(t, db.WriteServerMetrics(&ServerMetrics{
+		ServerID:  1,
+		Timestamp: firstTimestamp,
+		CPU:       10,
+	}))
+	db.Flush()
+	require.Equal(t, int32(1), addRowsCalls.Load())
+
+	before, err := db.QueryServerMetrics(1, MetricServerCPU, Period1Day)
+	require.NoError(t, err)
+	require.NotEmpty(t, before)
+
+	checker.value.Store(true)
+	require.NoError(t, db.WriteServerMetrics(&ServerMetrics{
+		ServerID:  1,
+		Timestamp: firstTimestamp.Add(2 * time.Second),
+		CPU:       20,
+	}))
+	assert.True(t, db.WritesPaused())
+	assert.Zero(t, bufferedRows(db.writer), "read-only writes must not accumulate in memory")
+	assert.Equal(t, int32(1), addRowsCalls.Load(), "read-only samples must not reach VictoriaMetrics")
+
+	afterDrop, err := db.QueryServerMetrics(1, MetricServerCPU, Period1Day)
+	require.NoError(t, err)
+	assert.Equal(t, before, afterDrop, "read-only mode must preserve existing query access")
+
+	checker.value.Store(false)
+	require.NoError(t, db.WriteServerMetrics(&ServerMetrics{
+		ServerID:  1,
+		Timestamp: firstTimestamp.Add(4 * time.Second),
+		CPU:       30,
+	}))
+	db.Flush()
+	assert.False(t, db.WritesPaused())
+	assert.Equal(t, int32(2), addRowsCalls.Load(), "writes must resume after storage leaves read-only mode")
+}
+
+func TestDiskFullAddRowsPanicPausesWrites(t *testing.T) {
+	db := newDiskGuardTestDB(t)
+	db.addRowsFn = func([]storage.MetricRow, uint8) {
+		panic("write data: no space left on device")
+	}
+
+	require.NoError(t, db.WriteServerMetrics(&ServerMetrics{
+		ServerID:  1,
+		Timestamp: time.Now(),
+		CPU:       10,
+	}))
+	assert.NotPanics(t, db.Flush)
+	assert.True(t, db.WritesPaused())
+
+	require.NoError(t, db.WriteServerMetrics(&ServerMetrics{
+		ServerID:  1,
+		Timestamp: time.Now().Add(time.Second),
+		CPU:       20,
+	}))
+	assert.Zero(t, bufferedRows(db.writer))
+}
+
+func TestNonDiskStoragePanicIsNotHidden(t *testing.T) {
+	db := newDiskGuardTestDB(t)
+	db.addRowsFn = func([]storage.MetricRow, uint8) {
+		panic("storage invariant failed")
+	}
+
+	require.NoError(t, db.WriteServerMetrics(&ServerMetrics{
+		ServerID:  1,
+		Timestamp: time.Now(),
+		CPU:       10,
+	}))
+	assert.PanicsWithValue(t, "storage invariant failed", db.Flush)
+}