Class MergeOperator

Namespace

RocksDbNet

Assembly

RocksDb.Net.dll

User-defined merge operator that enables read-modify-write semantics on values stored in RocksDb. Override FullMerge(ReadOnlySpan<byte>, bool, ReadOnlySpan<byte>, IReadOnlyList<byte[]>, out byte[]?) (and optionally PartialMerge(ReadOnlySpan<byte>, IReadOnlyList<byte[]>, out byte[]?)) to implement custom merge logic.

public abstract class MergeOperator : RocksDbHandle, IDisposable

Inheritance

object

RocksDbHandle

MergeOperator

Implements

IDisposable

Inherited Members

RocksDbHandle.Handle

RocksDbHandle.Owned

RocksDbHandle.IsDisposed

RocksDbHandle.PinGarbageCollector(string)

RocksDbHandle.IsPinned

RocksDbHandle.GetPinnedIntPtr()

RocksDbHandle.GetPinnedNameIntPtr()

RocksDbHandle.UnpinGarbageCollector()

RocksDbHandle.GetSelfFromPinnedIntPtr<T>(nint)

RocksDbHandle.GetNameFromPinnedIntPtr(nint)

RocksDbHandle.ThrowIfDisposed()

RocksDbHandle.Dispose()

RocksDbHandle.Dispose(bool)

RocksDbHandle.DisposeUnmanagedResources()

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

object.ToString()

Remarks

A merge operator is used with Merge(string, string, WriteOptions?) and similar overloads to combine new values with existing ones without a separate read step. Common use cases include counters, lists, and append-only logs.

Register a merge operator via MergeOperator or use SetUInt64AddMergeOperator() for the built-in 64-bit addition operator.

Constructors

MergeOperator(string)

Creates a merge operator with the given name.

protected MergeOperator(string name)

Parameters

name string

Identifies this operator in RocksDb's logs and options output. Unlike a comparator name it is not enforced on reopen, so a mismatch will not be caught for you: opening a database with a different merge operator than the one that wrote its operands silently produces wrong merges.

Methods

DisposeHandle()

Releases the native handle. Called during disposal.

protected override void DisposeHandle()

Remarks

Protected rather than public: it destroys the native object without marking this instance disposed or clearing the handle, so calling it from outside and then disposing normally would free the same pointer twice. It was the most Dispose-looking member on the type. Callers want Dispose().

FullMerge(ReadOnlySpan<byte>, bool, ReadOnlySpan<byte>, IReadOnlyList<byte[]>, out byte[]?)

Called to merge all accumulated operands with the existing value for a key.

public abstract bool FullMerge(ReadOnlySpan<byte> key, bool hasExistingValue, ReadOnlySpan<byte> existingValue, IReadOnlyList<byte[]> operands, out byte[]? newValue)

Parameters

key ReadOnlySpan<byte>

The key being merged.

hasExistingValue bool

true if the key has a pre-existing value.

existingValue ReadOnlySpan<byte>

The current value (valid only when hasExistingValue is true).

operands IReadOnlyList<byte[]>

The operands to merge, in chronological order. Managed copies, so they may be kept beyond the call.

newValue byte[]

Output: the result of the merge.

Returns

bool

true if the merge succeeded; false to signal failure.

PartialMerge(ReadOnlySpan<byte>, IReadOnlyList<byte[]>, out byte[]?)

Optional partial merge: combines a subset of operands before a full merge. Return false to fall back to FullMerge(ReadOnlySpan<byte>, bool, ReadOnlySpan<byte>, IReadOnlyList<byte[]>, out byte[]?).

public virtual bool PartialMerge(ReadOnlySpan<byte> key, IReadOnlyList<byte[]> operands, out byte[]? newValue)

Parameters

key ReadOnlySpan<byte>

The key being merged.

operands IReadOnlyList<byte[]>

The operands to combine, in chronological order. Managed copies, so they may be kept beyond the call.

newValue byte[]

Output: the combined operand.

Returns

bool

true if the operands were combined; false to leave it to FullMerge(ReadOnlySpan<byte>, bool, ReadOnlySpan<byte>, IReadOnlyList<byte[]>, out byte[]?).