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value.go

value.go - Overview​

This file defines the value log functionality for BadgerDB, including structs and functions for reading, writing, and managing value log files, garbage collection, and value thresholding.

Detailed Documentation​

Constants​

const (
	bitDelete                 byte = 1 << 0
	bitValuePointer           byte = 1 << 1
	bitDiscardEarlierVersions byte = 1 << 2
	bitMergeEntry byte = 1 << 3
	bitTxn    byte = 1 << 6
	bitFinTxn byte = 1 << 7

	mi int64 = 1 << 20

	vlogHeaderSize = 20
)
  • Purpose: Defines constants used within the value log.
    • bitDelete: Indicates that the key has been deleted.
    • bitValuePointer: Indicates that the value is stored in the value log.
    • bitDiscardEarlierVersions: Indicates that earlier versions can be discarded.
    • bitMergeEntry: Indicates an entry used by the merge operator.
    • bitTxn: Indicates that the entry is part of a transaction.
    • bitFinTxn: Indicates that the entry is the end of a transaction.
    • mi: Represents 1MB.
    • vlogHeaderSize: Size of the value log header.

errStop var​

var errStop = errors.New("Stop iteration")
  • Purpose: Error to stop iteration.

errTruncate var​

var errTruncate = errors.New("Do truncate")
  • Purpose: Error to indicate truncation.

logEntry type​

type logEntry func(e Entry, vp valuePointer) error
  • Purpose: Defines the signature for a function that processes a log entry.

safeRead struct​

type safeRead struct {
	k []byte
	v []byte

	recordOffset uint32
	lf           *logFile
}
  • Purpose: Helper struct for reading log entries.

hashReader struct​

type hashReader struct {
	r         io.Reader
	h         hash.Hash32
	bytesRead int
}
  • Purpose: Reader that also calculates a hash.

newHashReader func​

func newHashReader(r io.Reader) *hashReader {
  • Purpose: Creates a new hashReader.
  • Parameters:
    • r: io.Reader - The reader to wrap.
  • Returns: *hashReader - The new hashReader.

hashReader.Read func​

func (t *hashReader) Read(p []byte) (int, error) {
  • Purpose: Reads from the underlying reader and updates the hash.
  • Parameters:
    • p: []byte - The buffer to read into.
  • Returns:
    • int - The number of bytes read.
    • error - An error, if any.

hashReader.ReadByte func​

func (t *hashReader) ReadByte() (byte, error) {
  • Purpose: Reads a single byte from the underlying reader and updates the hash.
  • Returns:
    • byte - The byte read.
    • error - An error, if any.

hashReader.Sum32 func​

func (t *hashReader) Sum32() uint32 {
  • Purpose: Returns the sum32 of the underlying hash.
  • Returns: uint32 - The sum32 of the underlying hash.

safeRead.Entry func​

func (r *safeRead) Entry(reader io.Reader) (*Entry, error) {
  • Purpose: Reads an entry from the provided reader, validates the checksum, and decrypts (if necessary).
  • Parameters:
    • reader: io.Reader - The reader to read from.
  • Returns:
    • *Entry - The entry read.
    • error - An error, if any.

valueLog.rewrite func​

func (vlog *valueLog) rewrite(f *logFile) error {
  • Purpose: Rewrites a value log file by iterating over its entries and re-inserting them into the database if they are still valid and point to this file. This is used during garbage collection.
  • Parameters:
    • f: *logFile - The log file to rewrite.
  • Returns: error - An error, if any.

valueLog.incrIteratorCount func​

func (vlog *valueLog) incrIteratorCount() {
  • Purpose: Increments the number of active iterators.

valueLog.iteratorCount func​

func (vlog *valueLog) iteratorCount() int {
  • Purpose: Returns the number of active iterators.
  • Returns: int - The number of active iterators.

valueLog.decrIteratorCount func​

func (vlog *valueLog) decrIteratorCount() error {
  • Purpose: Decrements the number of active iterators. If the count reaches zero, it deletes any log files that were marked for deletion.
  • Returns: error - An error, if any.

valueLog.deleteLogFile func​

func (vlog *valueLog) deleteLogFile(lf *logFile) error {
  • Purpose: Deletes a log file.
  • Parameters:
    • lf: *logFile - The log file to delete.
  • Returns: error - An error, if any.

valueLog.dropAll func​

func (vlog *valueLog) dropAll() (int, error) {
  • Purpose: Drops all value log files.
  • Returns:
    • int - The number of files dropped.
    • error - An error, if any.

DB.valueThreshold func​

func (db *DB) valueThreshold() int64 {
  • Purpose: Returns the current value threshold.
  • Returns: int64 - The current value threshold.

valueLog struct​

type valueLog struct {
	dirPath string

	filesLock        sync.RWMutex
	filesMap         map[uint32]*logFile
	maxFid           uint32
	filesToBeDeleted []uint32
	numActiveIterators atomic.Int32

	db                *DB
	writableLogOffset atomic.Uint32
	numEntriesWritten uint32
	opt               Options

	garbageCh    chan struct{}
	discardStats *discardStats
}
  • Purpose: Manages value log files.
    • dirPath: Directory where value logs are stored.
    • filesLock: Read-write mutex for accessing file-related maps and slices.
    • filesMap: Map of file IDs to logFile structs.
    • maxFid: Maximum file ID.
    • filesToBeDeleted: Slice of file IDs to be deleted.
    • numActiveIterators: Atomic counter for active iterators.
    • db: Pointer to the DB struct.
    • writableLogOffset: Atomic offset for the writable log file.
    • numEntriesWritten: Number of entries written to the current log file.
    • opt: Database options.
    • garbageCh: Channel for garbage collection.
    • discardStats: Statistics for discarded entries.

vlogFilePath func​

func vlogFilePath(dirPath string, fid uint32) string {
  • Purpose: Generates the file path for a value log file.
  • Parameters:
    • dirPath: string - The directory path.
    • fid: uint32 - The file ID.
  • Returns: string - The file path.

valueLog.fpath func​

func (vlog *valueLog) fpath(fid uint32) string {
  • Purpose: Returns the file path for a given file ID.
  • Parameters:
    • fid: uint32 - The file ID.
  • Returns: string - The file path.

valueLog.populateFilesMap func​

func (vlog *valueLog) populateFilesMap() error {
  • Purpose: Populates the filesMap by reading the value log directory.
  • Returns: error - An error, if any.

valueLog.createVlogFile func​

func (vlog *valueLog) createVlogFile() (*logFile, error) {
  • Purpose: Creates a new value log file.
  • Returns:
    • *logFile - The new log file.
    • error - An error, if any.

errFile func​

func errFile(err error, path string, msg string) error {
  • Purpose: Formats an error message for file-related errors.
  • Parameters:
    • err: error - The error.
    • path: string - The file path.
    • msg: string - The error message.
  • Returns: error - The formatted error.

valueLog.init func​

func (vlog *valueLog) init(db *DB) {
  • Purpose: Initializes the value log struct.
  • Parameters:
    • db: *DB - The database instance.

valueLog.open func​

func (vlog *valueLog) open(db *DB) error {
  • Purpose: Opens the value log files.
  • Parameters:
    • db: *DB - The database instance.
  • Returns: error - An error, if any.

valueLog.Close func​

func (vlog *valueLog) Close() error {
  • Purpose: Closes all open value log files.
  • Returns: error - An error, if any.

valueLog.sortedFids func​

func (vlog *valueLog) sortedFids() []uint32 {
  • Purpose: Returns the sorted list of file IDs.
  • Returns: []uint32 - Sorted file IDs.

request struct​

type request struct {
	Entries []*Entry
	Ptrs []valuePointer
	Wg   sync.WaitGroup
	Err  error
	ref  atomic.Int32
}
  • Purpose: Represents a write request to the value log.
    • Entries: Entries to be written.
    • Ptrs: Value pointers for the written entries.
    • Wg: Wait group for asynchronous operations.
    • Err: Error encountered during the write.
    • ref: Atomic counter for tracking references to the request.

request.reset func​

func (req *request) reset() {
  • Purpose: Resets the request struct.

request.IncrRef func​

func (req *request) IncrRef() {
  • Purpose: Increments the reference count.

request.DecrRef func​

func (req *request) DecrRef() {
  • Purpose: Decrements the reference count.

request.Wait func​

func (req *request) Wait() error {
  • Purpose: Waits for the request to complete and returns any error.
  • Returns: error - An error, if any.

requests type​

type requests []*request
  • Purpose: Represents a slice of requests.

requests.DecrRef func​

func (reqs requests) DecrRef() {
  • Purpose: Decrements the reference count of all requests.

requests.IncrRef func​

func (reqs requests) IncrRef() {
  • Purpose: Increments the reference count of all requests.

valueLog.sync func​

func (vlog *valueLog) sync() error {
  • Purpose: Syncs the current value log file to disk.
  • Returns: error - An error, if any.

valueLog.woffset func​

func (vlog *valueLog) woffset() uint32 {
  • Purpose: Returns the current write offset.
  • Returns: uint32 - The current write offset.

valueLog.validateWrites func​

func (vlog *valueLog) validateWrites(reqs []*request) error {
  • Purpose: Validates that the writes in the given requests can fit into the value log file.
  • Parameters:
    • reqs: []*request - The requests to validate.
  • Returns: error - An error, if any.

estimateRequestSize func​

func estimateRequestSize(req *request) uint64 {
  • Purpose: Estimates the size required to write a request to the value log.
  • Parameters:
    • req: *request - The request to estimate.
  • Returns: uint64 - The estimated size.

valueLog.write func​

func (vlog *valueLog) write(reqs []*request) error {
  • Purpose: Writes the given requests to the value log.
  • Parameters:
    • reqs: []*request - The requests to write.
  • Returns: error - An error, if any.

valueLog.getFileRLocked func​

func (vlog *valueLog) getFileRLocked(vp valuePointer) (*logFile, error) {
  • Purpose: Gets a logFile and acquires a read lock on its mmap.
  • Parameters:
    • vp: valuePointer - Value pointer.
  • Returns:
    • *logFile - Log file.
    • error - An error, if any.

valueLog.Read func​

func (vlog *valueLog) Read(vp valuePointer, _ *y.Slice) ([]byte, func(), error) {
  • Purpose: Reads the value log at a given location.
  • Parameters:
    • vp: valuePointer - The location to read from.
    • _: `*