diff --git a/app/vlinsert/insertutils/common_params.go b/app/vlinsert/insertutils/common_params.go
index f2170da62..0077a19a0 100644
--- a/app/vlinsert/insertutils/common_params.go
+++ b/app/vlinsert/insertutils/common_params.go
@@ -2,7 +2,9 @@ package insertutils
 
 import (
 	"flag"
+	"fmt"
 	"net/http"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -31,6 +33,7 @@ type CommonParams struct {
 	MsgFields    []string
 	StreamFields []string
 	IgnoreFields []string
+	ExtraFields  []logstorage.Field
 
 	Debug           bool
 	DebugRequestURI string
@@ -45,48 +48,25 @@ func GetCommonParams(r *http.Request) (*CommonParams, error) {
 		return nil, err
 	}
 
-	// Extract time field name from _time_field query arg or header
 	timeField := "_time"
-	if tf := r.FormValue("_time_field"); tf != "" {
-		timeField = tf
-	} else if tf = r.Header.Get("VL-Time-Field"); tf != "" {
+	if tf := httputils.GetRequestValue(r, "_time_field", "VL-Time-Field"); tf != "" {
 		timeField = tf
 	}
 
-	// Extract message field name from _msg_field query arg or header
-	msgField := ""
-	if msgf := r.FormValue("_msg_field"); msgf != "" {
-		msgField = msgf
-	} else if msgf = r.Header.Get("VL-Msg-Field"); msgf != "" {
-		msgField = msgf
-	}
-	var msgFields []string
-	if msgField != "" {
-		msgFields = strings.Split(msgField, ",")
+	msgFields := httputils.GetArray(r, "_msg_field", "VL-Msg-Field")
+	streamFields := httputils.GetArray(r, "_stream_fields", "VL-Stream-Fields")
+	ignoreFields := httputils.GetArray(r, "ignore_fields", "VL-Ignore-Fields")
+
+	extraFields, err := getExtraFields(r)
+	if err != nil {
+		return nil, err
 	}
 
-	streamFields := httputils.GetArray(r, "_stream_fields")
-	if len(streamFields) == 0 {
-		if sf := r.Header.Get("VL-Stream-Fields"); len(sf) > 0 {
-			streamFields = strings.Split(sf, ",")
-		}
-	}
-	ignoreFields := httputils.GetArray(r, "ignore_fields")
-	if len(ignoreFields) == 0 {
-		if f := r.Header.Get("VL-Ignore-Fields"); len(f) > 0 {
-			ignoreFields = strings.Split(f, ",")
-		}
-	}
-
-	debug := httputils.GetBool(r, "debug")
-	if !debug {
-		if dh := r.Header.Get("VL-Debug"); len(dh) > 0 {
-			hv := strings.ToLower(dh)
-			switch hv {
-			case "", "0", "f", "false", "no":
-			default:
-				debug = true
-			}
+	debug := false
+	if dv := httputils.GetRequestValue(r, "debug", "VL-Debug"); dv != "" {
+		debug, err = strconv.ParseBool(dv)
+		if err != nil {
+			return nil, fmt.Errorf("cannot parse debug=%q: %w", dv, err)
 		}
 	}
 	debugRequestURI := ""
@@ -102,6 +82,7 @@ func GetCommonParams(r *http.Request) (*CommonParams, error) {
 		MsgFields:       msgFields,
 		StreamFields:    streamFields,
 		IgnoreFields:    ignoreFields,
+		ExtraFields:     extraFields,
 		Debug:           debug,
 		DebugRequestURI: debugRequestURI,
 		DebugRemoteAddr: debugRemoteAddr,
@@ -110,6 +91,26 @@ func GetCommonParams(r *http.Request) (*CommonParams, error) {
 	return cp, nil
 }
 
+func getExtraFields(r *http.Request) ([]logstorage.Field, error) {
+	efs := httputils.GetArray(r, "extra_fields", "VL-Extra-Fields")
+	if len(efs) == 0 {
+		return nil, nil
+	}
+
+	extraFields := make([]logstorage.Field, len(efs))
+	for i, ef := range efs {
+		n := strings.Index(ef, "=")
+		if n <= 0 || n == len(ef)-1 {
+			return nil, fmt.Errorf(`invalid extra_field format: %q; must be in the form "field=value"`, ef)
+		}
+		extraFields[i] = logstorage.Field{
+			Name:  ef[:n],
+			Value: ef[n+1:],
+		}
+	}
+	return extraFields, nil
+}
+
 // GetCommonParamsForSyslog returns common params needed for parsing syslog messages and storing them to the given tenantID.
 func GetCommonParamsForSyslog(tenantID logstorage.TenantID) *CommonParams {
 	// See https://docs.victoriametrics.com/victorialogs/logsql/#unpack_syslog-pipe
@@ -146,8 +147,6 @@ type logMessageProcessor struct {
 	stopCh        chan struct{}
 	lastFlushTime time.Time
 
-	tmpFields []logstorage.Field
-
 	cp *CommonParams
 	lr *logstorage.LogRows
 }
@@ -190,17 +189,6 @@ func (lmp *logMessageProcessor) AddRow(timestamp int64, fields []logstorage.Fiel
 		return
 	}
 
-	if *defaultMsgValue != "" && !hasMsgField(fields) {
-		// The log entry doesn't contain mandatory _msg field. Add _msg field with default value then
-		// according to https://docs.victoriametrics.com/victorialogs/keyconcepts/#message-field .
-		lmp.tmpFields = append(lmp.tmpFields[:0], fields...)
-		lmp.tmpFields = append(lmp.tmpFields, logstorage.Field{
-			Name:  "_msg",
-			Value: *defaultMsgValue,
-		})
-		fields = lmp.tmpFields
-	}
-
 	lmp.lr.MustAdd(lmp.cp.TenantID, timestamp, fields)
 	if lmp.cp.Debug {
 		s := lmp.lr.GetRowString(0)
@@ -214,15 +202,6 @@ func (lmp *logMessageProcessor) AddRow(timestamp int64, fields []logstorage.Fiel
 	}
 }
 
-func hasMsgField(fields []logstorage.Field) bool {
-	for _, f := range fields {
-		if f.Name == "_msg" {
-			return len(f.Value) > 0
-		}
-	}
-	return false
-}
-
 // flushLocked must be called under locked lmp.mu.
 func (lmp *logMessageProcessor) flushLocked() {
 	lmp.lastFlushTime = time.Now()
@@ -244,7 +223,7 @@ func (lmp *logMessageProcessor) MustClose() {
 //
 // MustClose() must be called on the returned LogMessageProcessor when it is no longer needed.
 func (cp *CommonParams) NewLogMessageProcessor() LogMessageProcessor {
-	lr := logstorage.GetLogRows(cp.StreamFields, cp.IgnoreFields)
+	lr := logstorage.GetLogRows(cp.StreamFields, cp.IgnoreFields, cp.ExtraFields, *defaultMsgValue)
 	lmp := &logMessageProcessor{
 		cp: cp,
 		lr: lr,
diff --git a/docs/VictoriaLogs/CHANGELOG.md b/docs/VictoriaLogs/CHANGELOG.md
index 5c3119782..13068027a 100644
--- a/docs/VictoriaLogs/CHANGELOG.md
+++ b/docs/VictoriaLogs/CHANGELOG.md
@@ -15,6 +15,8 @@ according to [these docs](https://docs.victoriametrics.com/victorialogs/quicksta
 
 ## tip
 
+* FEATURE: add an ability to specify extra fields for logs ingested via [HTTP-based data ingestion protocols](https://docs.victoriametrics.com/victorialogs/data-ingestion/#http-apis). See `extra_fields` query arg and `VL-Extra-Fields` HTTP header in [these docs](https://docs.victoriametrics.com/victorialogs/data-ingestion/#http-parameters).
+
 ## [v0.40.0](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v0.40.0-victorialogs)
 
 Released at 2024-10-31
diff --git a/docs/VictoriaLogs/data-ingestion/README.md b/docs/VictoriaLogs/data-ingestion/README.md
index 63d77fd8c..4be5d9a2e 100644
--- a/docs/VictoriaLogs/data-ingestion/README.md
+++ b/docs/VictoriaLogs/data-ingestion/README.md
@@ -189,66 +189,78 @@ HTTP query string parameters have priority over HTTP Headers.
 
 #### HTTP Query string parameters
 
-List of supported [Query string](https://en.wikipedia.org/wiki/Query_string) parameters:
+All the [HTTP-based data ingestion protocols](#http-apis) support the following [HTTP query string](https://en.wikipedia.org/wiki/Query_string) args:
 
-- `_msg_field` - it must contain the name of the [log field](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model)
-  with the [log message](https://docs.victoriametrics.com/victorialogs/keyconcepts/#message-field) generated by the log shipper.
+- `_msg_field` - the name of the [log field](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model)
+  containing [log message](https://docs.victoriametrics.com/victorialogs/keyconcepts/#message-field).
   This is usually the `message` field for Filebeat and Logstash.
 
   The `_msg_field` arg may contain comma-separated list of field names. In this case the first non-empty field from the list
   is treated as [log message](https://docs.victoriametrics.com/victorialogs/keyconcepts/#message-field).
 
-  If the `_msg_field` parameter isn't set, then VictoriaLogs reads the log message from the `_msg` field.
+  If the `_msg_field` arg isn't set, then VictoriaLogs reads the log message from the `_msg` field. If the `_msg` field is empty,
+  then it is set to `-defaultMsgValue` command-line flag value.
 
-- `_time_field` - it must contain the name of the [log field](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model)
-  with the [log timestamp](https://docs.victoriametrics.com/victorialogs/keyconcepts/#time-field) generated by the log shipper.
+- `_time_field` - the name of the [log field](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model)
+  containing [log timestamp](https://docs.victoriametrics.com/victorialogs/keyconcepts/#time-field).
   This is usually the `@timestamp` field for Filebeat and Logstash.
-  If the `_time_field` parameter isn't set, then VictoriaLogs reads the timestamp from the `_time` field.
-  If this field doesn't exist, then the current timestamp is used.
 
-- `_stream_fields` - it should contain comma-separated list of [log field](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model) names,
-  which uniquely identify every [log stream](https://docs.victoriametrics.com/victorialogs/keyconcepts/#stream-fields) collected the log shipper.
-  If the `_stream_fields` parameter isn't set, then all the ingested logs are written to default log stream - `{}`.
+  If the `_time_field` arg isn't set, then VictoriaLogs reads the timestamp from the `_time` field. If this field doesn't exist, then the current timestamp is used.
 
-- `ignore_fields` - this parameter may contain the list of [log field](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model) names,
+- `_stream_fields` - comma-separated list of [log field](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model) names,
+  which uniquely identify every [log stream](https://docs.victoriametrics.com/victorialogs/keyconcepts/#stream-fields).
+
+  If the `_stream_fields` arg isn't set, then all the ingested logs are written to default log stream - `{}`.
+
+- `ignore_fields` - an optional comma-separated list of [log field](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model) names,
   which must be ignored during data ingestion.
 
-- `debug` - if this parameter is set to `1`, then the ingested logs aren't stored in VictoriaLogs. Instead,
+- `extra_fields` - an optional comma-separated list [log fields](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model),
+  which must be added to all the ingested logs. The format of every `extra_fields` entry is `field_name=field_value`.
+  If the log entry contains fields from the `extra_fields`, then they are overwritten by the values specified in `extra_fields`.
+
+- `debug` - if this arg is set to `1`, then the ingested logs aren't stored in VictoriaLogs. Instead,
   the ingested data is logged by VictoriaLogs, so it can be investigated later.
 
 See also [HTTP headers](#http-headers).
 
 #### HTTP headers
 
-List of supported [HTTP Headers](https://en.wikipedia.org/wiki/List_of_HTTP_header_fields) parameters:
+All the [HTTP-based data ingestion protocols](#http-apis) support the following [HTTP Headers](https://en.wikipedia.org/wiki/List_of_HTTP_header_fields)
+additionally to [HTTP query args](#http-query-string-parameters):
 
-- `AccountID` - may contain the needed accountID of tenant to ingest data to. See [multitenancy docs](https://docs.victoriametrics.com/victorialogs/#multitenancy) for details.
+- `AccountID` - accountID of the tenant to ingest data to. See [multitenancy docs](https://docs.victoriametrics.com/victorialogs/#multitenancy) for details.
 
-- `ProjectID`- may contain the projectID needed of tenant to ingest data to. See [multitenancy docs](https://docs.victoriametrics.com/victorialogs/#multitenancy) for details.
-  VictoriaLogs accepts optional `AccountID` and `ProjectID` headers at [data ingestion HTTP APIs](#http-apis).
+- `ProjectID`- projectID of the tenant to ingest data to. See [multitenancy docs](https://docs.victoriametrics.com/victorialogs/#multitenancy) for details.
 
-- `VL-Msg-Field` - it must contain the name of the [log field](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model)
-  with the [log message](https://docs.victoriametrics.com/victorialogs/keyconcepts/#message-field) generated by the log shipper.
+- `VL-Msg-Field` - the name of the [log field](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model)
+  containing [log message](https://docs.victoriametrics.com/victorialogs/keyconcepts/#message-field).
   This is usually the `message` field for Filebeat and Logstash.
 
   The `VL-Msg-Field` header may contain comma-separated list of field names. In this case the first non-empty field from the list
   is treated as [log message](https://docs.victoriametrics.com/victorialogs/keyconcepts/#message-field).
 
-  If the `VL-Msg-Field` header isn't set, then VictoriaLogs reads the log message from the `_msg` field.
+  If the `VL-Msg-Field` header isn't set, then VictoriaLogs reads log message from the `_msg` field. If the `_msg` field is empty,
+  then it is set to `-defaultMsgValue` command-line flag value.
 
-- `VL-Time-Field` - it must contain the name of the [log field](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model)
-  with the [log timestamp](https://docs.victoriametrics.com/victorialogs/keyconcepts/#time-field) generated by the log shipper.
+- `VL-Time-Field` - the name of the [log field](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model)
+  containing [log timestamp](https://docs.victoriametrics.com/victorialogs/keyconcepts/#time-field).
   This is usually the `@timestamp` field for Filebeat and Logstash.
-  If the `VL-Time-Field` header isn't set, then VictoriaLogs reads the timestamp from the `_time` field.
-  If this field doesn't exist, then the current timestamp is used.
 
-- `VL-Stream-Fields` - it should contain comma-separated list of [log field](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model) names,
-  which uniquely identify every [log stream](https://docs.victoriametrics.com/victorialogs/keyconcepts/#stream-fields) collected the log shipper.
+  If the `VL-Time-Field` header isn't set, then VictoriaLogs reads the timestamp from the `_time` field. If this field doesn't exist, then the current timestamp is used.
+
+- `VL-Stream-Fields` - comma-separated list of [log field](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model) names,
+  which uniquely identify every [log stream](https://docs.victoriametrics.com/victorialogs/keyconcepts/#stream-fields).
+
   If the `VL-Stream-Fields` header isn't set, then all the ingested logs are written to default log stream - `{}`.
 
-- `VL-Ignore-Fields` - this parameter may contain the list of [log field](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model) names,
+- `VL-Ignore-Fields` - an optional comma-separated list of [log field](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model) names,
   which must be ignored during data ingestion.
 
+- `VL-Extra-Field` - an optional comma-separated list of [log fields](https://docs.victoriametrics.com/victorialogs/keyconcepts/#data-model),
+  which must be added to all the ingested logs. The format of every `extra_fields` entry is `field_name=field_value`.
+  If the log entry contains fields from the `extra_fields`, then they are overwritten by the values specified in `extra_fields`.
+
 - `VL-Debug` - if this parameter is set to `1`, then the ingested logs aren't stored in VictoriaLogs. Instead,
   the ingested data is logged by VictoriaLogs, so it can be investigated later.
 
diff --git a/lib/httputils/array.go b/lib/httputils/array.go
index 5d61f3f7e..ca5c5b7d4 100644
--- a/lib/httputils/array.go
+++ b/lib/httputils/array.go
@@ -5,11 +5,20 @@ import (
 	"strings"
 )
 
-// GetArray returns an array of comma-separated values from r arg with the argKey name.
-func GetArray(r *http.Request, argKey string) []string {
-	v := r.FormValue(argKey)
+// GetArray returns an array of comma-separated values from r with the argKey quey arg or with headerKey header.
+func GetArray(r *http.Request, argKey, headerKey string) []string {
+	v := GetRequestValue(r, argKey, headerKey)
 	if v == "" {
 		return nil
 	}
 	return strings.Split(v, ",")
 }
+
+// GetRequestValue returns r value for the given argKey query arg or for the given headerKey header.
+func GetRequestValue(r *http.Request, argKey, headerKey string) string {
+	v := r.FormValue(argKey)
+	if v == "" {
+		v = r.Header.Get(headerKey)
+	}
+	return v
+}
diff --git a/lib/logstorage/filter_stream_id_test.go b/lib/logstorage/filter_stream_id_test.go
index 78fc357fc..c6628f4b8 100644
--- a/lib/logstorage/filter_stream_id_test.go
+++ b/lib/logstorage/filter_stream_id_test.go
@@ -84,7 +84,7 @@ func testFilterMatchForStreamID(t *testing.T, f filter, expectedRowIdxs []int) {
 
 func generateTestLogStreams(s *Storage, tenantID TenantID, getMsgValue func(int) string, rowsCount, streamsCount int) {
 	streamFields := []string{"host", "app"}
-	lr := GetLogRows(streamFields, nil)
+	lr := GetLogRows(streamFields, nil, nil, "")
 	var fields []Field
 	for i := range rowsCount {
 		fields = append(fields[:0], Field{
diff --git a/lib/logstorage/filter_test.go b/lib/logstorage/filter_test.go
index 90f288280..017abca1d 100644
--- a/lib/logstorage/filter_test.go
+++ b/lib/logstorage/filter_test.go
@@ -249,7 +249,7 @@ func generateRowsFromColumns(s *Storage, tenantID TenantID, columns []column) {
 		"job",
 		"instance",
 	}
-	lr := GetLogRows(streamTags, nil)
+	lr := GetLogRows(streamTags, nil, nil, "")
 	var fields []Field
 	for i := range columns[0].values {
 		// Add stream tags
diff --git a/lib/logstorage/filter_time_test.go b/lib/logstorage/filter_time_test.go
index 0ad7b013e..ffb1ed2c6 100644
--- a/lib/logstorage/filter_time_test.go
+++ b/lib/logstorage/filter_time_test.go
@@ -123,7 +123,7 @@ func testFilterMatchForTimestamps(t *testing.T, timestamps []int64, f filter, ex
 }
 
 func generateRowsFromTimestamps(s *Storage, tenantID TenantID, timestamps []int64, getValue func(rowIdx int) string) {
-	lr := GetLogRows(nil, nil)
+	lr := GetLogRows(nil, nil, nil, "")
 	var fields []Field
 	for i, timestamp := range timestamps {
 		fields = append(fields[:0], Field{
diff --git a/lib/logstorage/inmemory_part_test.go b/lib/logstorage/inmemory_part_test.go
index c2f62c99c..ce17fa149 100644
--- a/lib/logstorage/inmemory_part_test.go
+++ b/lib/logstorage/inmemory_part_test.go
@@ -22,7 +22,7 @@ func TestInmemoryPartMustInitFromRows(t *testing.T) {
 
 		// make a copy of lr - it is used for comapring the results later,
 		// since lr may be modified by inmemoryPart.mustInitFromRows()
-		lrOrig := GetLogRows(nil, nil)
+		lrOrig := GetLogRows(nil, nil, nil, "")
 		for i, timestamp := range lr.timestamps {
 			if timestamp < minTimestampExpected {
 				minTimestampExpected = timestamp
@@ -72,7 +72,7 @@ func TestInmemoryPartMustInitFromRows(t *testing.T) {
 		}
 	}
 
-	f(GetLogRows(nil, nil), 0, 0)
+	f(GetLogRows(nil, nil, nil, ""), 0, 0)
 
 	// Check how inmemoryPart works with a single stream
 	f(newTestLogRows(1, 1, 0), 1, 0.7)
@@ -108,7 +108,7 @@ func TestInmemoryPartInitFromBlockStreamReaders(t *testing.T) {
 		maxTimestampExpected := int64(math.MinInt64)
 
 		// make a copy of rrss in order to compare the results after merge.
-		lrOrig := GetLogRows(nil, nil)
+		lrOrig := GetLogRows(nil, nil, nil, "")
 		for _, lr := range lrs {
 			uncompressedSizeBytesExpected += uncompressedRowsSizeBytes(lr.rows)
 			rowsCountExpected += len(lr.timestamps)
@@ -188,8 +188,8 @@ func TestInmemoryPartInitFromBlockStreamReaders(t *testing.T) {
 
 	// Check empty readers
 	f(nil, 0, 0)
-	f([]*LogRows{GetLogRows(nil, nil)}, 0, 0)
-	f([]*LogRows{GetLogRows(nil, nil), GetLogRows(nil, nil)}, 0, 0)
+	f([]*LogRows{GetLogRows(nil, nil, nil, "")}, 0, 0)
+	f([]*LogRows{GetLogRows(nil, nil, nil, ""), GetLogRows(nil, nil, nil, "")}, 0, 0)
 
 	// Check merge with a single reader
 	f([]*LogRows{newTestLogRows(1, 1, 0)}, 1, 0.7)
@@ -235,7 +235,7 @@ func newTestLogRows(streams, rowsPerStream int, seed int64) *LogRows {
 	streamTags := []string{
 		"some-stream-tag",
 	}
-	lr := GetLogRows(streamTags, nil)
+	lr := GetLogRows(streamTags, nil, nil, "")
 	rng := rand.New(rand.NewSource(seed))
 	var fields []Field
 	for i := 0; i < streams; i++ {
@@ -322,7 +322,7 @@ func checkEqualRows(lrResult, lrOrig *LogRows) error {
 //
 // This function is for testing and debugging purposes only.
 func (mp *inmemoryPart) readLogRows(sbu *stringsBlockUnmarshaler, vd *valuesDecoder) *LogRows {
-	lr := GetLogRows(nil, nil)
+	lr := GetLogRows(nil, nil, nil, "")
 	bsr := getBlockStreamReader()
 	defer putBlockStreamReader(bsr)
 	bsr.MustInitFromInmemoryPart(mp)
diff --git a/lib/logstorage/log_rows.go b/lib/logstorage/log_rows.go
index bf5553b84..2b642c199 100644
--- a/lib/logstorage/log_rows.go
+++ b/lib/logstorage/log_rows.go
@@ -3,16 +3,14 @@ package logstorage
 import (
 	"sort"
 	"sync"
-
-	"github.com/VictoriaMetrics/VictoriaMetrics/lib/bytesutil"
 )
 
 // LogRows holds a set of rows needed for Storage.MustAddRows
 //
 // LogRows must be obtained via GetLogRows()
 type LogRows struct {
-	// buf holds all the bytes referred by items in LogRows
-	buf []byte
+	// a holds all the bytes referred by items in LogRows
+	a arena
 
 	// fieldsBuf holds all the fields referred by items in LogRows
 	fieldsBuf []Field
@@ -37,6 +35,15 @@ type LogRows struct {
 
 	// ignoreFields contains names for log fields, which must be skipped during data ingestion
 	ignoreFields map[string]struct{}
+
+	// extraFields contains extra fields to add to all the logs at MustAdd().
+	extraFields []Field
+
+	// extraStreamFields contains extraFields, which must be treated as stream fields.
+	extraStreamFields []Field
+
+	// defaultMsgValue contains default value for missing _msg field
+	defaultMsgValue string
 }
 
 type sortedFields []Field
@@ -79,11 +86,16 @@ func (lr *LogRows) Reset() {
 	for k := range ifs {
 		delete(ifs, k)
 	}
+
+	lr.extraFields = nil
+	lr.extraStreamFields = lr.extraStreamFields[:0]
+
+	lr.defaultMsgValue = ""
 }
 
 // ResetKeepSettings resets rows stored in lr, while keeping its settings passed to GetLogRows().
 func (lr *LogRows) ResetKeepSettings() {
-	lr.buf = lr.buf[:0]
+	lr.a.reset()
 
 	fb := lr.fieldsBuf
 	for i := range fb {
@@ -116,7 +128,7 @@ func (lr *LogRows) ResetKeepSettings() {
 
 // NeedFlush returns true if lr contains too much data, so it must be flushed to the storage.
 func (lr *LogRows) NeedFlush() bool {
-	return len(lr.buf) > (maxUncompressedBlockSize/8)*7
+	return len(lr.a.b) > (maxUncompressedBlockSize/8)*7
 }
 
 // MustAdd adds a log entry with the given args to lr.
@@ -126,15 +138,16 @@ func (lr *LogRows) NeedFlush() bool {
 //
 // field names longer than MaxFieldNameSize are automatically truncated to MaxFieldNameSize length.
 func (lr *LogRows) MustAdd(tenantID TenantID, timestamp int64, fields []Field) {
-	// Compose StreamTags from fields according to lr.streamFields
-	sfs := lr.streamFields
+	// Compose StreamTags from fields according to lr.streamFields and lr.extraStreamFields
 	st := GetStreamTags()
-	for i := range fields {
-		f := &fields[i]
-		if _, ok := sfs[f.Name]; ok {
+	for _, f := range fields {
+		if _, ok := lr.streamFields[f.Name]; ok {
 			st.Add(f.Name, f.Value)
 		}
 	}
+	for _, f := range lr.extraStreamFields {
+		st.Add(f.Name, f.Value)
+	}
 
 	// Marshal StreamTags
 	bb := bbPool.Get()
@@ -152,23 +165,45 @@ func (lr *LogRows) MustAdd(tenantID TenantID, timestamp int64, fields []Field) {
 }
 
 func (lr *LogRows) mustAddInternal(sid streamID, timestamp int64, fields []Field, streamTagsCanonical []byte) {
-	buf := lr.buf
-	bufLen := len(buf)
-	buf = append(buf, streamTagsCanonical...)
+	streamTagsCanonicalCopy := lr.a.copyBytes(streamTagsCanonical)
+	lr.streamTagsCanonicals = append(lr.streamTagsCanonicals, streamTagsCanonicalCopy)
 
-	lr.streamTagsCanonicals = append(lr.streamTagsCanonicals, buf[bufLen:])
 	lr.streamIDs = append(lr.streamIDs, sid)
 	lr.timestamps = append(lr.timestamps, timestamp)
 
-	// Store all the fields
-	ifs := lr.ignoreFields
+	fieldsLen := len(lr.fieldsBuf)
+	hasMsgField := lr.addFieldsInternal(fields, lr.ignoreFields)
+	if lr.addFieldsInternal(lr.extraFields, nil) {
+		hasMsgField = true
+	}
+
+	// Add optional default _msg field
+	if !hasMsgField && lr.defaultMsgValue != "" {
+		value := lr.a.copyString(lr.defaultMsgValue)
+		lr.fieldsBuf = append(lr.fieldsBuf, Field{
+			Value: value,
+		})
+	}
+
+	// Sort fields by name
+	lr.sf = lr.fieldsBuf[fieldsLen:]
+	sort.Sort(&lr.sf)
+
+	// Add log row with sorted fields to lr.rows
+	lr.rows = append(lr.rows, lr.sf)
+}
+
+func (lr *LogRows) addFieldsInternal(fields []Field, ignoreFields map[string]struct{}) bool {
+	if len(fields) == 0 {
+		return false
+	}
+
 	fb := lr.fieldsBuf
-	fieldsLen := len(fb)
+	hasMsgField := false
 	for i := range fields {
 		f := &fields[i]
 
-		if _, ok := ifs[f.Name]; ok {
-			// Skip fields from the ifs map
+		if _, ok := ignoreFields[f.Name]; ok {
 			continue
 		}
 		if f.Value == "" {
@@ -179,26 +214,20 @@ func (lr *LogRows) mustAddInternal(sid streamID, timestamp int64, fields []Field
 		fb = append(fb, Field{})
 		dstField := &fb[len(fb)-1]
 
-		bufLen = len(buf)
 		fieldName := f.Name
 		if len(fieldName) > MaxFieldNameSize {
 			fieldName = fieldName[:MaxFieldNameSize]
 		}
-		if fieldName != "_msg" {
-			buf = append(buf, fieldName...)
+		if fieldName == "_msg" {
+			fieldName = ""
+			hasMsgField = true
 		}
-		dstField.Name = bytesutil.ToUnsafeString(buf[bufLen:])
-
-		bufLen = len(buf)
-		buf = append(buf, f.Value...)
-		dstField.Value = bytesutil.ToUnsafeString(buf[bufLen:])
+		dstField.Name = lr.a.copyString(fieldName)
+		dstField.Value = lr.a.copyString(f.Value)
 	}
-	lr.sf = fb[fieldsLen:]
-	sort.Sort(&lr.sf)
-	lr.rows = append(lr.rows, lr.sf)
-
 	lr.fieldsBuf = fb
-	lr.buf = buf
+
+	return hasMsgField
 }
 
 // GetRowString returns string representation of the row with the given idx.
@@ -225,9 +254,11 @@ func (lr *LogRows) GetRowString(idx int) string {
 //
 // streamFields is a set of field names, which must be associated with the stream.
 // ignoreFields is a set of field names, which must be ignored during data ingestion.
+// extraFields is a set of fields, which must be added to all the logs passed to MustAdd().
+// defaultMsgValue is the default value to store in non-existing or empty _msg.
 //
 // Return back it to the pool with PutLogRows() when it is no longer needed.
-func GetLogRows(streamFields, ignoreFields []string) *LogRows {
+func GetLogRows(streamFields, ignoreFields []string, extraFields []Field, defaultMsgValue string) *LogRows {
 	v := logRowsPool.Get()
 	if v == nil {
 		v = &LogRows{}
@@ -244,6 +275,14 @@ func GetLogRows(streamFields, ignoreFields []string) *LogRows {
 		sfs[f] = struct{}{}
 	}
 
+	// Initialize extraStreamFields
+	for _, f := range extraFields {
+		if _, ok := sfs[f.Name]; ok {
+			lr.extraStreamFields = append(lr.extraStreamFields, f)
+			delete(sfs, f.Name)
+		}
+	}
+
 	// Initialize ignoreFields
 	ifs := lr.ignoreFields
 	if ifs == nil {
@@ -253,8 +292,17 @@ func GetLogRows(streamFields, ignoreFields []string) *LogRows {
 	for _, f := range ignoreFields {
 		if f != "" {
 			ifs[f] = struct{}{}
+			delete(sfs, f)
 		}
 	}
+	for _, f := range extraFields {
+		// Extra fields must orverride the existing fields for the sake of consistency and security,
+		// so the client won't be able to override them.
+		ifs[f.Name] = struct{}{}
+	}
+
+	lr.extraFields = extraFields
+	lr.defaultMsgValue = defaultMsgValue
 
 	return lr
 }
diff --git a/lib/logstorage/log_rows_test.go b/lib/logstorage/log_rows_test.go
new file mode 100644
index 000000000..d7f112701
--- /dev/null
+++ b/lib/logstorage/log_rows_test.go
@@ -0,0 +1,145 @@
+package logstorage
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestLogRows_DefaultMsgValue(t *testing.T) {
+	type opts struct {
+		rows []string
+
+		streamFields    []string
+		ignoreFields    []string
+		extraFields     []Field
+		defaultMsgValue string
+
+		resultExpected []string
+	}
+
+	f := func(o opts) {
+		t.Helper()
+
+		lr := GetLogRows(o.streamFields, o.ignoreFields, o.extraFields, o.defaultMsgValue)
+		defer PutLogRows(lr)
+
+		tid := TenantID{
+			AccountID: 123,
+			ProjectID: 456,
+		}
+
+		p := GetJSONParser()
+		defer PutJSONParser(p)
+		for i, r := range o.rows {
+			if err := p.ParseLogMessage([]byte(r)); err != nil {
+				t.Fatalf("unexpected error when parsing %q: %s", r, err)
+			}
+			timestamp := int64(i)*1_000 + 1
+			lr.MustAdd(tid, timestamp, p.Fields)
+		}
+
+		var result []string
+		for i := range o.rows {
+			s := lr.GetRowString(i)
+			result = append(result, s)
+		}
+		if !reflect.DeepEqual(result, o.resultExpected) {
+			t.Fatalf("unexpected result\ngot\n%v\nwant\n%v", result, o.resultExpected)
+		}
+	}
+
+	var o opts
+
+	f(o)
+
+	// default options
+	o = opts{
+		rows: []string{
+			`{"foo":"bar"}`,
+			`{}`,
+			`{"foo":"bar","a":"b"}`,
+		},
+		resultExpected: []string{
+			`{"_stream":"{}","_time":"1970-01-01T00:00:00.000000001Z","foo":"bar"}`,
+			`{"_stream":"{}","_time":"1970-01-01T00:00:00.000001001Z"}`,
+			`{"_stream":"{}","_time":"1970-01-01T00:00:00.000002001Z","a":"b","foo":"bar"}`,
+		},
+	}
+	f(o)
+
+	// stream fields
+	o = opts{
+		rows: []string{
+			`{"x":"y","foo":"bar"}`,
+			`{"x":"y","foo":"bar","abc":"de"}`,
+			`{}`,
+		},
+		streamFields: []string{"foo", "abc"},
+		resultExpected: []string{
+			`{"_stream":"{foo=\"bar\"}","_time":"1970-01-01T00:00:00.000000001Z","foo":"bar","x":"y"}`,
+			`{"_stream":"{abc=\"de\",foo=\"bar\"}","_time":"1970-01-01T00:00:00.000001001Z","abc":"de","foo":"bar","x":"y"}`,
+			`{"_stream":"{}","_time":"1970-01-01T00:00:00.000002001Z"}`,
+		},
+	}
+	f(o)
+
+	// ignore fields
+	o = opts{
+		rows: []string{
+			`{"x":"y","foo":"bar"}`,
+			`{"x":"y"}`,
+			`{}`,
+		},
+		streamFields: []string{"foo", "abc", "x"},
+		ignoreFields: []string{"foo"},
+		resultExpected: []string{
+			`{"_stream":"{x=\"y\"}","_time":"1970-01-01T00:00:00.000000001Z","x":"y"}`,
+			`{"_stream":"{x=\"y\"}","_time":"1970-01-01T00:00:00.000001001Z","x":"y"}`,
+			`{"_stream":"{}","_time":"1970-01-01T00:00:00.000002001Z"}`,
+		},
+	}
+	f(o)
+
+	// extra fields
+	o = opts{
+		rows: []string{
+			`{"x":"y","foo":"bar"}`,
+			`{}`,
+		},
+		streamFields: []string{"foo", "abc", "x"},
+		ignoreFields: []string{"foo"},
+		extraFields: []Field{
+			{
+				Name:  "foo",
+				Value: "test",
+			},
+			{
+				Name:  "abc",
+				Value: "1234",
+			},
+		},
+		resultExpected: []string{
+			`{"_stream":"{abc=\"1234\",foo=\"test\",x=\"y\"}","_time":"1970-01-01T00:00:00.000000001Z","abc":"1234","foo":"test","x":"y"}`,
+			`{"_stream":"{abc=\"1234\",foo=\"test\"}","_time":"1970-01-01T00:00:00.000001001Z","abc":"1234","foo":"test"}`,
+		},
+	}
+	f(o)
+
+	// default _msg value
+	o = opts{
+		rows: []string{
+			`{"x":"y","foo":"bar"}`,
+			`{"_msg":"ppp"}`,
+			`{"abc":"ppp"}`,
+		},
+		streamFields:    []string{"abc", "x"},
+		defaultMsgValue: "qwert",
+		resultExpected: []string{
+			`{"_msg":"qwert","_stream":"{x=\"y\"}","_time":"1970-01-01T00:00:00.000000001Z","foo":"bar","x":"y"}`,
+			`{"_msg":"ppp","_stream":"{}","_time":"1970-01-01T00:00:00.000001001Z"}`,
+			`{"_msg":"qwert","_stream":"{abc=\"ppp\"}","_time":"1970-01-01T00:00:00.000002001Z","abc":"ppp"}`,
+		},
+	}
+	f(o)
+
+}
diff --git a/lib/logstorage/log_rows_timing_test.go b/lib/logstorage/log_rows_timing_test.go
index 55a726e1b..32023e120 100644
--- a/lib/logstorage/log_rows_timing_test.go
+++ b/lib/logstorage/log_rows_timing_test.go
@@ -52,7 +52,7 @@ func BenchmarkLogRowsMustAdd(b *testing.B) {
 }
 
 func benchmarkLogRowsMustAdd(rows [][]Field, streamFields []string) {
-	lr := GetLogRows(streamFields, nil)
+	lr := GetLogRows(streamFields, nil, nil, "")
 	var tid TenantID
 	for i, fields := range rows {
 		tid.AccountID = uint32(i)
diff --git a/lib/logstorage/storage.go b/lib/logstorage/storage.go
index a5de2b88e..7b2f75cb2 100644
--- a/lib/logstorage/storage.go
+++ b/lib/logstorage/storage.go
@@ -549,7 +549,7 @@ func (s *Storage) MustAddRows(lr *LogRows) {
 		}
 		lrPart := m[day]
 		if lrPart == nil {
-			lrPart = GetLogRows(nil, nil)
+			lrPart = GetLogRows(nil, nil, nil, "")
 			m[day] = lrPart
 		}
 		lrPart.mustAddInternal(lr.streamIDs[i], ts, lr.rows[i], lr.streamTagsCanonicals[i])
diff --git a/lib/logstorage/storage_search_test.go b/lib/logstorage/storage_search_test.go
index 35530309e..8e5375b9a 100644
--- a/lib/logstorage/storage_search_test.go
+++ b/lib/logstorage/storage_search_test.go
@@ -47,7 +47,7 @@ func TestStorageRunQuery(t *testing.T) {
 		for j := 0; j < streamsPerTenant; j++ {
 			streamIDValue := fmt.Sprintf("stream_id=%d", j)
 			for k := 0; k < blocksPerStream; k++ {
-				lr := GetLogRows(streamTags, nil)
+				lr := GetLogRows(streamTags, nil, nil, "")
 				for m := 0; m < rowsPerBlock; m++ {
 					timestamp := baseTimestamp + int64(m)*1e9 + int64(k)
 					// Append stream fields
@@ -774,7 +774,7 @@ func TestStorageSearch(t *testing.T) {
 		allTenantIDs = append(allTenantIDs, tenantID)
 		for j := 0; j < streamsPerTenant; j++ {
 			for k := 0; k < blocksPerStream; k++ {
-				lr := GetLogRows(streamTags, nil)
+				lr := GetLogRows(streamTags, nil, nil, "")
 				for m := 0; m < rowsPerBlock; m++ {
 					timestamp := baseTimestamp + int64(m)*1e9 + int64(k)
 					// Append stream fields