Scan update function, and tick based timestamps

Author: halgari

CHANGELOG.md

@@ -1,5 +1,10 @@
 ## Changelog
 
+### 0.9.100 - 27/1/2025
+* Switch timestamps over to storing time as `DateTimeOffset.Ticks` so that we have the most accurate times possible
+* Provide a new `ScanUpdate` feature that can be used for data migration and conversions. Allows datoms to be deleted or 
+updated based on a simple function interface
+
 ### 0.9.99 - 21/1/2025
 * Provide a way to open a RocksDB backend in read-only mode
 * Default to zstd compression for RocksDB vs the previous snappy compression

src/NexusMods.MnemonicDB.Abstractions/Attributes/TimestampAttribute.cs

@@ -11,8 +11,8 @@ namespace NexusMods.MnemonicDB.Abstractions.Attributes;
 public sealed class TimestampAttribute(string ns, string name) : ScalarAttribute<DateTimeOffset, long, Int64Serializer>(ns, name)
 {
     /// <inheritdoc />
-    protected override long ToLowLevel(DateTimeOffset value) => value.ToUnixTimeMilliseconds();
+    protected override long ToLowLevel(DateTimeOffset value) => value.UtcTicks;
 
     /// <inheritdoc />
-    protected override DateTimeOffset FromLowLevel(long value, AttributeResolver resolver) => DateTimeOffset.FromUnixTimeMilliseconds(value);
+    protected override DateTimeOffset FromLowLevel(long value, AttributeResolver resolver) => new(value, TimeSpan.Zero);
 }

src/NexusMods.MnemonicDB/Connection.cs

@@ -264,7 +264,7 @@ public async Task<ICommitResult> FlushAndCompact()
     /// <inheritdoc />
     public Task UpdateSchema(params IAttribute[] attribute)
     {
-        return Transact(new SchemaMigration(attribute));
+        return Transact(new ScanUpdate(attribute));
     }
 
     public IObservable<IChangeSet<Datom, DatomKey>> ObserveDatoms(SliceDescriptor descriptor)
@@ -327,7 +327,7 @@ private void Bootstrap()
             AttributeCache.Reset(initialDb);
 
             var declaredAttributes = AttributeResolver.DefinedAttributes.OrderBy(a => a.Id.Id).ToArray();
-            _store.Transact(new SchemaMigration(declaredAttributes));
+            _store.Transact(new ScanUpdate(declaredAttributes));
 
             _dbStreamDisposable = ProcessUpdates(_store.TxLog)
                 .Subscribe();

src/NexusMods.MnemonicDB/InternalTxFunctions/SchemaMigration.cs renamed to src/NexusMods.MnemonicDB/InternalTxFunctions/ScanUpdate.cs

@@ -11,12 +11,12 @@
 
 namespace NexusMods.MnemonicDB.InternalTxFunctions;
 
-internal class SchemaMigration : AInternalFn
+internal class ScanUpdate : AInternalFn
 {
     private readonly IAttribute[] _declaredAttributes;
     private ulong _tempId = PartitionId.Temp.MakeEntityId(1).Value;
 
-    public SchemaMigration(IAttribute[] attributes)
+    public ScanUpdate(IAttribute[] attributes)
     {
         _declaredAttributes = attributes;
     }

src/NexusMods.MnemonicDB/Storage/DatomStore.cs

@@ -386,7 +386,7 @@ internal void LogDatoms<TSource>(IWriteBatch batch, TSource datoms,  bool advanc
     /// <exception cref="NotImplementedException"></exception>
     private void LogTx(IWriteBatch batch)
     {
-        MemoryMarshal.Write(_txScratchSpace.Span, _timeProvider.GetUtcNow().ToUnixTimeMilliseconds());
+        MemoryMarshal.Write(_txScratchSpace.Span, _timeProvider.GetUtcNow().UtcTicks);
         var id = EntityId.From(_thisTx.Value);
         var keyPrefix = new KeyPrefix(id, AttributeCache.GetAttributeId(MnemonicDB.Abstractions.BuiltInEntities.Transaction.Timestamp.Id), _thisTx, false, ValueTag.Int64);
         var datom = new Datom(keyPrefix, _txScratchSpace[..sizeof(long)]);