MB-72082: introduce new stats handler for zap layer

stats.go

@@ -0,0 +1,84 @@
+//	Copyright (c) 2026 Couchbase, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package segment
+
+import (
+	"reflect"
+	"sync/atomic"
+	"unsafe"
+)
+
+const StatsKey = "zap_stats"
+
+type Stats struct {
+	TotNewRootDocsProcessed uint64
+	TotNewDocsProcessed     uint64
+	TotNewDocsIndexed       uint64
+	TotNewDocsDropped       uint64
+	TotNewVectorsProcessed  uint64
+
+	TotPersistBeg    uint64
+	TotPersistEnd    uint64
+	TotPersistErrors uint64
+
+	TotMergesBeg          uint64
+	TotMergesEnd          uint64
+	TotMergesErrors       uint64
+	TotMergeInputSegments uint64
+	TotMergeOutputDocs    uint64
+	TotMergeDroppedDocs   uint64
+
+	TotVecSectionMergesBegin            uint64
+	TotVecSectionMergesEnd              uint64
+	TotVecSectionMergeTime              uint64
+	TotVecSectionVecsReconstructed      uint64
+	TotVecSectionIVFIndexesCreated      uint64
+	TotVecSectionFlatIndexesCreated     uint64
+	TotVecSectionTrainingTime           uint64
+	TotVecSectionFastMerges             uint64
+	TotVecSectionFastMergeErrs          uint64
+	TotVecSectionNaiveMerges            uint64
+	TotVecSectionMetadataBytesWritten   uint64
+	TotVecSectionFloatIndexBytesWritten uint64
+	TotVecSectionVecsDeleted            uint64
+	TotVecSectionFieldsIndexed          uint64
+	TotVecSectionTrainOps               uint64
+	TotVecSectionIndexWriteTime         uint64
+	TotVecSectionVecsProcessedTime      uint64
+
+	TotVecSectionTrainingPhaseVecsProcessedTime uint64
+	TotVecSectionTrainingPhaseTrainingTime      uint64
+
+	TotOpenBeg    uint64
+	TotOpenEnd    uint64
+	TotOpenErrors uint64
+
+	TotSegmentsClosed uint64
+}
+
+func (s *Stats) StatsMap() map[string]interface{} {
+	svet := reflect.TypeOf(*s)
+	n := svet.NumField()
+	m := make(map[string]interface{}, n)
+	base := unsafe.Pointer(s)
+	for i := 0; i < n; i++ {
+		field := svet.Field(i)
+
+		// use unsafe.Pointer to avoid heap allocs, safe to do this here since all the stats
+		// enforced to be uint64
+		p := (*uint64)(unsafe.Pointer(uintptr(base) + field.Offset))
+		m[field.Name] = atomic.LoadUint64(p)
+	}
+	return m
+}