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file.go
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file.go
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package lsmtree
import (
"fmt"
"io"
"os"
"github.com/krasun/rbytree"
)
func putEntry(file *os.File, key []byte, value []byte) error {
return appendToFile(file, encodePut(key, value))
}
func deleteEntry(file *os.File, key []byte) error {
return appendToFile(file, encodeDelete(key))
}
func appendToFile(file *os.File, data []byte) error {
// for safety, since the file is open in read-write mode
if _, err := file.Seek(0, 2); err != nil {
return fmt.Errorf("failed to seek to the end: %w", err)
}
if _, err := file.Write(data); err != nil {
return fmt.Errorf("failed to write to the file: %w", err)
}
if err := file.Sync(); err != nil {
return fmt.Errorf("failed to sync the file: %w", err)
}
return nil
}
func loadMemTable(file *os.File) (*rbytree.Tree, error) {
memTable := rbytree.New()
deleteKeys := make([][]byte, 0)
offset := 0
for {
var encodedEntryLen [8]byte
n, err := file.ReadAt(encodedEntryLen[:], int64(offset))
if err != nil && err != io.EOF {
return nil, fmt.Errorf("failed to read: %w", err)
}
if n < 8 && err == io.EOF {
for _, deleteKey := range deleteKeys {
// we need to mark deleted key, to make sure
// it will be written to the sorted file
memTable.Put(deleteKey, nil)
}
return memTable, nil
}
offset += n
entryLen := decodeLen(encodedEntryLen[:])
encodedEntry := make([]byte, entryLen)
n, err = file.ReadAt(encodedEntry, int64(offset))
if n < entryLen {
return nil, fmt.Errorf("the file is corrupted, failed to read entry: %w", err)
}
offset += n
key, value, deleted := decode(encodedEntry)
if deleted {
deleteKeys = append(deleteKeys, key)
} else {
memTable.Put(key, value)
}
}
}