public async Task <IEnumerable <(long, T)> > GetBatch(long startingOffset, int batchSize, CancellationToken cancellationToken)
{
Preconditions.CheckRange(batchSize, 1, nameof(batchSize));
if (startingOffset < this.headOffset)
{
startingOffset = this.headOffset;
}
if (this.IsEmpty() || this.tailOffset < startingOffset)
{
return(Enumerable.Empty <(long, T)>());
}
var batch = new List <(long, T)>();
byte[] startingKey = StoreUtils.GetKeyFromOffset(startingOffset);
await this.entityStore.IterateBatch(
startingKey,
batchSize,
(k, v) =>
{
long offsetFromKey = StoreUtils.GetOffsetFromKey(k);
batch.Add((offsetFromKey, v));
return(Task.CompletedTask);
},
cancellationToken);
return(batch);
}
public static async Task <ISequentialStore <T> > Create(IEntityStore <byte[], T> entityStore, long defaultHeadOffset)
{
Preconditions.CheckNotNull(entityStore, nameof(entityStore));
Option <(byte[] key, T value)> firstEntry = await entityStore.GetFirstEntry(CancellationToken.None);
Option <(byte[] key, T value)> lastEntry = await entityStore.GetLastEntry(CancellationToken.None);
long MapLocalFunction((byte[] key, T) e) => StoreUtils.GetOffsetFromKey(e.key);
long headOffset = firstEntry.Map(MapLocalFunction).GetOrElse(defaultHeadOffset);
long tailOffset = lastEntry.Map(MapLocalFunction).GetOrElse(defaultHeadOffset - 1);
var sequentialStore = new SequentialStore <T>(entityStore, headOffset, tailOffset);
return(sequentialStore);
}