/// <summary>
/// Initializes cross partition query execution context by initializing the necessary document producers.
/// </summary>
/// <param name="collectionRid">The collection to drain from.</param>
/// <param name="partitionKeyRanges">The partitions to target.</param>
/// <param name="initialPageSize">The page size to start the document producers off with.</param>
/// <param name="querySpecForInit">The query specification for the rewritten query.</param>
/// <param name="targetRangeToContinuationMap">Map from partition to it's corresponding continuation token.</param>
/// <param name="deferFirstPage">Whether or not we should defer the fetch of the first page from each partition.</param>
/// <param name="filter">The filter to inject in the predicate.</param>
/// <param name="filterCallback">The callback used to filter each partition.</param>
/// <param name="token">The cancellation token.</param>
/// <returns>A task to await on.</returns>
protected async Task InitializeAsync(
string collectionRid,
IReadOnlyList <PartitionKeyRange> partitionKeyRanges,
int initialPageSize,
SqlQuerySpec querySpecForInit,
Dictionary <string, string> targetRangeToContinuationMap,
bool deferFirstPage,
string filter,
Func <DocumentProducerTree, Task> filterCallback,
CancellationToken token)
{
CollectionCache collectionCache = await this.Client.GetCollectionCacheAsync();
INameValueCollection requestHeaders = await this.CreateCommonHeadersAsync(this.GetFeedOptions(null));
this.TraceInformation(string.Format(
CultureInfo.InvariantCulture,
"parallel~contextbase.initializeasync, queryspec {0}, maxbuffereditemcount: {1}, target partitionkeyrange count: {2}, maximumconcurrencylevel: {3}, documentproducer initial page size {4}",
JsonConvert.SerializeObject(this.querySpec, DefaultJsonSerializationSettings.Value),
this.actualMaxBufferedItemCount,
partitionKeyRanges.Count,
this.comparableTaskScheduler.MaximumConcurrencyLevel,
initialPageSize));
List <DocumentProducerTree> documentProducerTrees = new List <DocumentProducerTree>();
foreach (PartitionKeyRange partitionKeyRange in partitionKeyRanges)
{
string initialContinuationToken = (targetRangeToContinuationMap != null && targetRangeToContinuationMap.ContainsKey(partitionKeyRange.Id)) ? targetRangeToContinuationMap[partitionKeyRange.Id] : null;
DocumentProducerTree documentProducerTree = new DocumentProducerTree(
partitionKeyRange,
//// Create Document Service Request callback
(pkRange, continuationToken, pageSize) =>
{
INameValueCollection headers = requestHeaders.Clone();
headers[HttpConstants.HttpHeaders.Continuation] = continuationToken;
headers[HttpConstants.HttpHeaders.PageSize] = pageSize.ToString(CultureInfo.InvariantCulture);
return(this.CreateDocumentServiceRequest(
headers,
querySpecForInit,
pkRange,
collectionRid));
},
this.ExecuteRequestLazyAsync,
//// Retry policy callback
() => new NonRetriableInvalidPartitionExceptionRetryPolicy(collectionCache, this.Client.ResetSessionTokenRetryPolicy.GetRequestPolicy()),
this.OnDocumentProducerTreeCompleteFetching,
this.documentProducerForest.Comparer as IComparer <DocumentProducerTree>,
this.equalityComparer,
this.Client,
deferFirstPage,
collectionRid,
initialPageSize,
initialContinuationToken);
documentProducerTree.Filter = filter;
// Prefetch if necessary, and populate consume queue.
if (this.CanPrefetch)
{
this.TryScheduleFetch(documentProducerTree);
}
documentProducerTrees.Add(documentProducerTree);
}
// Using loop fisson so that we can load the document producers in parallel
foreach (DocumentProducerTree documentProducerTree in documentProducerTrees)
{
if (!deferFirstPage)
{
await documentProducerTree.MoveNextIfNotSplit(token);
}
if (filterCallback != null)
{
await filterCallback(documentProducerTree);
}
if (documentProducerTree.HasMoreResults)
{
this.documentProducerForest.Enqueue(documentProducerTree);
}
}
}
