bring in khatru and eventstore.

eventstore/mmm/freeranges.go

@@ -0,0 +1,68 @@
+package mmm
+
+import (
+	"fmt"
+	"slices"
+
+	"github.com/PowerDNS/lmdb-go/lmdb"
+)
+
+func (b *MultiMmapManager) mergeNewFreeRange(pos position) (isAtEnd bool) {
+	// before adding check if we can merge this with some other range
+	// (to merge means to delete the previous and add a new one)
+	toDelete := make([]int, 0, 2)
+	for f, fr := range b.freeRanges {
+		if pos.start+uint64(pos.size) == fr.start {
+			// [new_pos_to_be_freed][existing_fr] -> merge!
+			toDelete = append(toDelete, f)
+			pos.size = pos.size + fr.size
+		} else if fr.start+uint64(fr.size) == pos.start {
+			// [existing_fr][new_pos_to_be_freed] -> merge!
+			toDelete = append(toDelete, f)
+			pos.start = fr.start
+			pos.size = fr.size + pos.size
+		}
+	}
+	slices.SortFunc(toDelete, func(a, b int) int { return b - a })
+	for _, idx := range toDelete {
+		b.freeRanges = slices.Delete(b.freeRanges, idx, idx+1)
+	}
+
+	// when we're at the end of a file we just delete everything and don't add new free ranges
+	// the caller will truncate the mmap file and adjust the position accordingly
+	if pos.start+uint64(pos.size) == b.mmapfEnd {
+		return true
+	}
+
+	b.addNewFreeRange(pos)
+	return false
+}
+
+func (b *MultiMmapManager) addNewFreeRange(pos position) {
+	// update freeranges slice in memory
+	idx, _ := slices.BinarySearchFunc(b.freeRanges, pos, func(item, target position) int {
+		if item.size > target.size {
+			return 1
+		} else if target.size > item.size {
+			return -1
+		} else if item.start > target.start {
+			return 1
+		} else {
+			return -1
+		}
+	})
+	b.freeRanges = slices.Insert(b.freeRanges, idx, pos)
+}
+
+func (b *MultiMmapManager) saveFreeRanges(txn *lmdb.Txn) error {
+	// save to database
+	valReserve, err := txn.PutReserve(b.stuff, FREERANGES_KEY, len(b.freeRanges)*12, 0)
+	if err != nil {
+		return fmt.Errorf("on put freeranges: %w", err)
+	}
+	for f, fr := range b.freeRanges {
+		bytesFromPosition(valReserve[f*12:], fr)
+	}
+
+	return nil
+}