/// <inheritdoc />
public IEnumerable <IReadOnlyList <ContentHashWithLastAccessTimeAndReplicaCount> > GetLruPages(
Context context,
IReadOnlyList <ContentHashWithLastAccessTimeAndReplicaCount> contentHashesWithInfo)
{
Contract.Assert(_configuration.HasReadOrWriteMode(ContentLocationMode.LocalLocationStore), "GetLruPages can only be called when local location store is enabled");
if (contentHashesWithInfo.Count != 0)
{
var first = contentHashesWithInfo[0];
var last = contentHashesWithInfo[contentHashesWithInfo.Count - 1];
context.Debug($"GetLruPages start with contentHashesWithInfo.Count={contentHashesWithInfo.Count}, firstAge={first.Age}, lastAge={last.Age}");
}
var operationContext = new OperationContext(context);
var pageSize = _configuration.EvictionWindowSize;
// Assume that EffectiveLastAccessTime will always have a value.
var comparer = Comparer <ContentHashWithLastAccessTimeAndReplicaCount> .Create((c1, c2) => c1.EffectiveLastAccessTime.Value.CompareTo(c2.EffectiveLastAccessTime.Value));
Func <List <ContentHashWithLastAccessTimeAndReplicaCount>, IEnumerable <ContentHashWithLastAccessTimeAndReplicaCount> > query =
page => _localLocationStore.GetEffectiveLastAccessTimes(operationContext, page.SelectList(v => new ContentHashWithLastAccessTime(v.ContentHash, v.LastAccessTime))).ThrowIfFailure();
// We make sure that we select a set of the newer content, to ensure that we at least look at newer content to see if it should be
// evicted first due to having a high number of replicas. We do this by looking at the start as well as at middle of the list.
var localOldest = contentHashesWithInfo.Take(contentHashesWithInfo.Count / 2).QueryAndOrderInPages(pageSize, comparer, query);
var localMid = contentHashesWithInfo.SkipOptimized(contentHashesWithInfo.Count / 2).QueryAndOrderInPages(pageSize, comparer, query);
var mergedEnumerables = NuCacheCollectionUtilities.MergeOrdered(localOldest, localMid, comparer);
return(mergedEnumerables.GetPages(pageSize));
}
/// <inheritdoc />
public IEnumerable <ContentHashWithLastAccessTimeAndReplicaCount> GetHashesInEvictionOrder(
Context context,
IReadOnlyList <ContentHashWithLastAccessTimeAndReplicaCount> contentHashesWithInfo)
{
Contract.Assert(_configuration.HasReadOrWriteMode(ContentLocationMode.LocalLocationStore), "GetLruPages can only be called when local location store is enabled");
// Counter for successful eviction candidates. Different than total number of eviction candidates, because this only increments when candidate is above minimum eviction age
int evictionCount = 0;
// contentHashesWithInfo is literally all data inside the content directory. The Purger wants to remove
// content until we are within quota. Here we return batches of content to be removed.
// contentHashesWithInfo is sorted by (local) LastAccessTime in descending order (Least Recently Used).
if (contentHashesWithInfo.Count != 0)
{
var first = contentHashesWithInfo[0];
var last = contentHashesWithInfo[contentHashesWithInfo.Count - 1];
context.Debug($"{nameof(GetHashesInEvictionOrder)} start with contentHashesWithInfo.Count={contentHashesWithInfo.Count}, firstAge={first.Age(_clock)}, lastAge={last.Age(_clock)}");
}
var operationContext = new OperationContext(context);
// Ideally, we want to remove content we know won't be used again for quite a while. We don't have that
// information, so we use an evictability metric. Here we obtain and sort by that evictability metric.
// Assume that EffectiveLastAccessTime will always have a value.
var comparer = Comparer <ContentHashWithLastAccessTimeAndReplicaCount> .Create((c1, c2) => c1.EffectiveLastAccessTime.Value.CompareTo(c2.EffectiveLastAccessTime.Value));
Func <List <ContentHashWithLastAccessTimeAndReplicaCount>, IEnumerable <ContentHashWithLastAccessTimeAndReplicaCount> > intoEffectiveLastAccessTimes =
page => _localLocationStore.GetEffectiveLastAccessTimes(
operationContext,
page.SelectList(v => new ContentHashWithLastAccessTime(v.ContentHash, v.LastAccessTime))).ThrowIfFailure();
// We make sure that we select a set of the newer content, to ensure that we at least look at newer content to see if it should be
// evicted first due to having a high number of replicas. We do this by looking at the start as well as at middle of the list.
var oldestByEvictability = contentHashesWithInfo.Take(contentHashesWithInfo.Count / 2).ApproximateSort(comparer, intoEffectiveLastAccessTimes, _configuration.EvictionPoolSize, _configuration.EvictionWindowSize, _configuration.EvictionRemovalFraction);
var youngestByEvictability = contentHashesWithInfo.SkipOptimized(contentHashesWithInfo.Count / 2).ApproximateSort(comparer, intoEffectiveLastAccessTimes, _configuration.EvictionPoolSize, _configuration.EvictionWindowSize, _configuration.EvictionRemovalFraction);
return(NuCacheCollectionUtilities.MergeOrdered(oldestByEvictability, youngestByEvictability, comparer)
.Where((candidate, index) => IsPassEvictionAge(context, candidate, _configuration.EvictionMinAge, index, ref evictionCount)));
}
