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merge.go

merge.go - Overview​

This file defines the MergeOperator for BadgerDB, enabling users to merge values associated with a key using a custom merge function. It handles asynchronous compaction of merged values.

Detailed Documentation​

MergeOperator​

type MergeOperator struct {
    sync.RWMutex
    f      MergeFunc
    db     *DB
    key    []byte
    closer *z.Closer
}
  • Purpose: Represents a Badger merge operator. It encapsulates the merge function, the database instance, the key to merge, and a closer for managing the compaction goroutine.

MergeFunc​

type MergeFunc func(existingVal, newVal []byte) []byte
  • Purpose: Defines the function signature for merging two byte slices. It takes an existing value and a new value, and returns the merged result.
  • Parameters:
    • existingVal: The existing value (byte slice).
    • newVal: The new value to merge (byte slice).
  • Returns: The merged value (byte slice).

(*DB) GetMergeOperator​

func (db *DB) GetMergeOperator(key []byte, f MergeFunc, dur time.Duration) *MergeOperator
  • Purpose: Creates a new MergeOperator for a given key and starts a goroutine to perform periodic compactions using the provided merge function.
  • Parameters:
    • key: The key to associate with the merge operator (byte slice).
    • f: The MergeFunc to use for merging values.
    • dur: The duration between compactions.
  • Returns: A pointer to the new MergeOperator.

(*MergeOperator) iterateAndMerge​

func (op *MergeOperator) iterateAndMerge() (newVal []byte, latest uint64, err error)
  • Purpose: Iterates through all versions of a key, merging them using the merge function.
  • Returns:
    • newVal: The final merged value (byte slice).
    • latest: The version of the latest value.
    • err: An error, if any occurred. Returns ErrKeyNotFound if the key doesn't exist, errNoMerge if there is only one version.

(*MergeOperator) compact​

func (op *MergeOperator) compact() error
  • Purpose: Performs a compaction by merging all versions of the key and writing the result back to the database.
  • Returns: An error, if any occurred during the compaction process.

(*MergeOperator) runCompactions​

func (op *MergeOperator) runCompactions(dur time.Duration)
  • Purpose: Runs compactions periodically using a ticker.
  • Parameters:
    • dur: The duration between compactions.

(*MergeOperator) Add​

func (op *MergeOperator) Add(val []byte) error
  • Purpose: Adds a value to be merged with the existing values for the key.
  • Parameters:
    • val: The value to add (byte slice).
  • Returns: An error, if any occurred during the update.

(*MergeOperator) Get​

func (op *MergeOperator) Get() ([]byte, error)
  • Purpose: Retrieves the latest merged value for the key.
  • Returns:
    • The merged value (byte slice).
    • An error, if any occurred. Returns ErrKeyNotFound if the key has no value.

(*MergeOperator) Stop​

func (op *MergeOperator) Stop()
  • Purpose: Stops the background compaction goroutine.

Getting Started Relevance​