RPageStorageDaos.cxx

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/// \file RPageStorageDaos.cxx
/// \ingroup NTuple ROOT7
/// \author Javier Lopez-Gomez <j.lopez@cern.ch>
/// \date 2020-11-03
/// \warning This is part of the ROOT 7 prototype! It will change without notice. It might trigger earthquakes. Feedback
/// is welcome!
 
/*************************************************************************
 * Copyright (C) 1995-2021, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/
 
#include <ROOT/RCluster.hxx>
#include <ROOT/RClusterPool.hxx>
#include <ROOT/RField.hxx>
#include <ROOT/RLogger.hxx>
#include <ROOT/RNTupleDescriptor.hxx>
#include <ROOT/RNTupleModel.hxx>
#include <ROOT/RNTupleSerialize.hxx>
#include <ROOT/RNTupleUtil.hxx>
#include <ROOT/RNTupleZip.hxx>
#include <ROOT/RPage.hxx>
#include <ROOT/RPageAllocator.hxx>
#include <ROOT/RPagePool.hxx>
#include <ROOT/RDaos.hxx>
#include <ROOT/RPageStorageDaos.hxx>
 
#include <RVersion.h>
#include <TError.h>
 
#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <limits>
#include <utility>
#include <regex>
 
namespace {
struct RDaosURI {
   /// \brief UUID of the DAOS pool
   std::string fPoolUuid;
   /// \brief Ranks of the service replicas, separated by `_`
   std::string fSvcReplicas;
   /// \brief UUID of the container for this RNTuple
   std::string fContainerUuid;
};
 
/**
  \brief Parse a DAOS RNTuple URI of the form 'daos://pool-uuid:svc_replicas/container_uuid'.
*/
RDaosURI ParseDaosURI(std::string_view uri)
{
   std::regex re("daos://([[:xdigit:]-]+):([[:digit:]_]+)/([[:xdigit:]-]+)");
   std::cmatch m;
   if (!std::regex_match(uri.data(), m, re))
      throw ROOT::Experimental::RException(R__FAIL("Invalid DAOS pool URI."));
   return { m[1], m[2], m[3] };
}
 
/// \brief Some random distribution/attribute key.  TODO: apply recommended schema, i.e.
/// an OID for each cluster + a dkey for each page.
static constexpr std::uint64_t kDistributionKey = 0x5a3c69f0cafe4a11;
static constexpr std::uint64_t kAttributeKey = 0x4243544b5344422d;
 
static constexpr daos_obj_id_t kOidAnchor{std::uint64_t(-1), 0};
static constexpr daos_obj_id_t kOidHeader{std::uint64_t(-2), 0};
static constexpr daos_obj_id_t kOidFooter{std::uint64_t(-3), 0};
// The page list offset needs to be a positive 64bit integer because we currently use
// the object ID for the offset in the locator
// TODO(jblomer): use object store locators
// TODO(jblomer): add support for multiple page list envelopes from multiple cluster groups
static constexpr daos_obj_id_t kOidPageList{std::numeric_limits<int64_t>::max(), 0};
 
static constexpr daos_oclass_id_t kCidMetadata = OC_SX;
} // namespace
 
 
////////////////////////////////////////////////////////////////////////////////
 
 
std::uint32_t
ROOT::Experimental::Detail::RDaosNTupleAnchor::Serialize(void *buffer) const
{
   using RNTupleSerializer = ROOT::Experimental::Internal::RNTupleSerializer;
   if (buffer != nullptr) {
      auto bytes = reinterpret_cast<unsigned char *>(buffer);
      bytes += RNTupleSerializer::SerializeUInt32(fVersion, bytes);
      bytes += RNTupleSerializer::SerializeUInt32(fNBytesHeader, bytes);
      bytes += RNTupleSerializer::SerializeUInt32(fLenHeader, bytes);
      bytes += RNTupleSerializer::SerializeUInt32(fNBytesFooter, bytes);
      bytes += RNTupleSerializer::SerializeUInt32(fLenFooter, bytes);
      bytes += RNTupleSerializer::SerializeString(fObjClass, bytes);
   }
   return RNTupleSerializer::SerializeString(fObjClass, nullptr) + 20;
}
 
ROOT::Experimental::RResult<std::uint32_t>
ROOT::Experimental::Detail::RDaosNTupleAnchor::Deserialize(const void *buffer, std::uint32_t bufSize)
{
   if (bufSize < 20)
      return R__FAIL("DAOS anchor too short");
 
   using RNTupleSerializer = ROOT::Experimental::Internal::RNTupleSerializer;
   auto bytes = reinterpret_cast<const unsigned char *>(buffer);
   bytes += RNTupleSerializer::DeserializeUInt32(bytes, fVersion);
   bytes += RNTupleSerializer::DeserializeUInt32(bytes, fNBytesHeader);
   bytes += RNTupleSerializer::DeserializeUInt32(bytes, fLenHeader);
   bytes += RNTupleSerializer::DeserializeUInt32(bytes, fNBytesFooter);
   bytes += RNTupleSerializer::DeserializeUInt32(bytes, fLenFooter);
   auto result = RNTupleSerializer::DeserializeString(bytes, bufSize - 20, fObjClass);
   if (!result)
      return R__FORWARD_ERROR(result);
   return result.Unwrap() + 20;
}
 
std::uint32_t
ROOT::Experimental::Detail::RDaosNTupleAnchor::GetSize()
{
   return RDaosNTupleAnchor().Serialize(nullptr)
      + ROOT::Experimental::Detail::RDaosObject::ObjClassId::kOCNameMaxLength;
}
 
 
////////////////////////////////////////////////////////////////////////////////
 
 
ROOT::Experimental::Detail::RPageSinkDaos::RPageSinkDaos(std::string_view ntupleName, std::string_view uri,
   const RNTupleWriteOptions &options)
   : RPageSink(ntupleName, options)
   , fPageAllocator(std::make_unique<RPageAllocatorHeap>())
   , fURI(uri)
{
   R__LOG_WARNING(NTupleLog()) << "The DAOS backend is experimental and still under development. " <<
      "Do not store real data with this version of RNTuple!";
   fCompressor = std::make_unique<RNTupleCompressor>();
   EnableDefaultMetrics("RPageSinkDaos");
}
 
 
ROOT::Experimental::Detail::RPageSinkDaos::~RPageSinkDaos() = default;
 
 
void ROOT::Experimental::Detail::RPageSinkDaos::CreateImpl(const RNTupleModel & /* model */)
{
   auto opts = dynamic_cast<RNTupleWriteOptionsDaos *>(fOptions.get());
   fNTupleAnchor.fObjClass = opts ? opts->GetObjectClass() : RNTupleWriteOptionsDaos().GetObjectClass();
   auto oclass = RDaosObject::ObjClassId(fNTupleAnchor.fObjClass);
   if (oclass.IsUnknown())
      throw ROOT::Experimental::RException(R__FAIL("Unknown object class " + fNTupleAnchor.fObjClass));
 
   auto args = ParseDaosURI(fURI);
   auto pool = std::make_shared<RDaosPool>(args.fPoolUuid, args.fSvcReplicas);
   fDaosContainer = std::make_unique<RDaosContainer>(pool, args.fContainerUuid, /*create =*/ true);
   fDaosContainer->SetDefaultObjectClass(oclass);
 
   const auto &descriptor = fDescriptorBuilder.GetDescriptor();
   fSerializationContext = Internal::RNTupleSerializer::SerializeHeaderV1(nullptr, descriptor);
   auto buffer = std::make_unique<unsigned char[]>(fSerializationContext.GetHeaderSize());
   fSerializationContext = Internal::RNTupleSerializer::SerializeHeaderV1(buffer.get(), descriptor);
 
   auto zipBuffer = std::make_unique<unsigned char[]>(fSerializationContext.GetHeaderSize());
   auto szZipHeader =
      fCompressor->Zip(buffer.get(), fSerializationContext.GetHeaderSize(), GetWriteOptions().GetCompression(),
                       [&zipBuffer](const void *b, size_t n, size_t o) { memcpy(zipBuffer.get() + o, b, n); });
   WriteNTupleHeader(zipBuffer.get(), szZipHeader, fSerializationContext.GetHeaderSize());
}
 
 
ROOT::Experimental::RNTupleLocator
ROOT::Experimental::Detail::RPageSinkDaos::CommitPageImpl(ColumnHandle_t columnHandle, const RPage &page)
{
   auto element = columnHandle.fColumn->GetElement();
   RPageStorage::RSealedPage sealedPage;
   {
      RNTupleAtomicTimer timer(fCounters->fTimeWallZip, fCounters->fTimeCpuZip);
      sealedPage = SealPage(page, *element, GetWriteOptions().GetCompression());
   }
 
   fCounters->fSzZip.Add(page.GetNBytes());
   return CommitSealedPageImpl(columnHandle.fId, sealedPage);
}
 
 
ROOT::Experimental::RNTupleLocator
ROOT::Experimental::Detail::RPageSinkDaos::CommitSealedPageImpl(
   DescriptorId_t /*columnId*/, const RPageStorage::RSealedPage &sealedPage)
{
   auto offsetData = fOid.fetch_add(1);
   {
      RNTupleAtomicTimer timer(fCounters->fTimeWallWrite, fCounters->fTimeCpuWrite);
      fDaosContainer->WriteSingleAkey(sealedPage.fBuffer, sealedPage.fSize,
                                      {offsetData, 0}, kDistributionKey, kAttributeKey);
   }
 
   RNTupleLocator result;
   result.fPosition = offsetData;
   result.fBytesOnStorage = sealedPage.fSize;
   fCounters->fNPageCommitted.Inc();
   fCounters->fSzWritePayload.Add(sealedPage.fSize);
   fNBytesCurrentCluster += sealedPage.fSize;
   return result;
}
 
 
std::uint64_t
ROOT::Experimental::Detail::RPageSinkDaos::CommitClusterImpl(ROOT::Experimental::NTupleSize_t /* nEntries */)
{
   return std::exchange(fNBytesCurrentCluster, 0);
}
 
 
void ROOT::Experimental::Detail::RPageSinkDaos::CommitDatasetImpl()
{
   const auto &descriptor = fDescriptorBuilder.GetDescriptor();
 
   std::vector<DescriptorId_t> physClusterIDs;
   for (const auto &c : descriptor.GetClusterIterable()) {
      physClusterIDs.emplace_back(fSerializationContext.MapClusterId(c.GetId()));
   }
 
   auto szPageList =
      Internal::RNTupleSerializer::SerializePageListV1(nullptr, descriptor, physClusterIDs, fSerializationContext);
   auto bufPageList = std::make_unique<unsigned char[]>(szPageList);
   Internal::RNTupleSerializer::SerializePageListV1(bufPageList.get(), descriptor, physClusterIDs,
                                                    fSerializationContext);
 
   auto bufPageListZip = std::make_unique<unsigned char[]>(szPageList);
   auto szPageListZip = fCompressor->Zip(bufPageList.get(), szPageList, GetWriteOptions().GetCompression(),
                                         RNTupleCompressor::MakeMemCopyWriter(bufPageListZip.get()));
   fDaosContainer->WriteSingleAkey(bufPageListZip.get(), szPageListZip, kOidPageList, kDistributionKey, kAttributeKey,
                                   kCidMetadata);
 
   Internal::RNTupleSerializer::REnvelopeLink pageListEnvelope;
   pageListEnvelope.fUnzippedSize = szPageList;
   pageListEnvelope.fLocator.fPosition = kOidPageList.lo;
   pageListEnvelope.fLocator.fBytesOnStorage = szPageListZip;
   fSerializationContext.AddClusterGroup(physClusterIDs.size(), pageListEnvelope);
 
   auto szFooter = Internal::RNTupleSerializer::SerializeFooterV1(nullptr, descriptor, fSerializationContext);
   auto bufFooter = std::make_unique<unsigned char[]>(szFooter);
   Internal::RNTupleSerializer::SerializeFooterV1(bufFooter.get(), descriptor, fSerializationContext);
 
   auto bufFooterZip = std::make_unique<unsigned char[]>(szFooter);
   auto szFooterZip = fCompressor->Zip(bufFooter.get(), szFooter, GetWriteOptions().GetCompression(),
                                       RNTupleCompressor::MakeMemCopyWriter(bufFooterZip.get()));
   WriteNTupleFooter(bufFooterZip.get(), szFooterZip, szFooter);
   WriteNTupleAnchor();
}
 
 
void ROOT::Experimental::Detail::RPageSinkDaos::WriteNTupleHeader(
      const void *data, size_t nbytes, size_t lenHeader)
{
   fDaosContainer->WriteSingleAkey(data, nbytes, kOidHeader, kDistributionKey,
                                   kAttributeKey, kCidMetadata);
   fNTupleAnchor.fLenHeader = lenHeader;
   fNTupleAnchor.fNBytesHeader = nbytes;
}
 
void ROOT::Experimental::Detail::RPageSinkDaos::WriteNTupleFooter(
      const void *data, size_t nbytes, size_t lenFooter)
{
   fDaosContainer->WriteSingleAkey(data, nbytes, kOidFooter, kDistributionKey,
                                   kAttributeKey, kCidMetadata);
   fNTupleAnchor.fLenFooter = lenFooter;
   fNTupleAnchor.fNBytesFooter = nbytes;
}
 
void ROOT::Experimental::Detail::RPageSinkDaos::WriteNTupleAnchor() {
   const auto ntplSize = RDaosNTupleAnchor::GetSize();
   auto buffer = std::make_unique<unsigned char[]>(ntplSize);
   fNTupleAnchor.Serialize(buffer.get());
   fDaosContainer->WriteSingleAkey(buffer.get(), ntplSize, kOidAnchor, kDistributionKey,
                                   kAttributeKey, kCidMetadata);
}
 
ROOT::Experimental::Detail::RPage
ROOT::Experimental::Detail::RPageSinkDaos::ReservePage(ColumnHandle_t columnHandle, std::size_t nElements)
{
   if (nElements == 0)
      throw RException(R__FAIL("invalid call: request empty page"));
   auto elementSize = columnHandle.fColumn->GetElement()->GetSize();
   return fPageAllocator->NewPage(columnHandle.fId, elementSize, nElements);
}
 
void ROOT::Experimental::Detail::RPageSinkDaos::ReleasePage(RPage &page)
{
   fPageAllocator->DeletePage(page);
}
 
 
////////////////////////////////////////////////////////////////////////////////
 
 
ROOT::Experimental::Detail::RPage ROOT::Experimental::Detail::RPageAllocatorDaos::NewPage(
   ColumnId_t columnId, void *mem, std::size_t elementSize, std::size_t nElements)
{
   RPage newPage(columnId, mem, elementSize, nElements);
   newPage.GrowUnchecked(nElements);
   return newPage;
}
 
void ROOT::Experimental::Detail::RPageAllocatorDaos::DeletePage(const RPage& page)
{
   if (page.IsNull())
      return;
   delete[] reinterpret_cast<unsigned char *>(page.GetBuffer());
}
 
 
////////////////////////////////////////////////////////////////////////////////
 
 
ROOT::Experimental::Detail::RPageSourceDaos::RPageSourceDaos(std::string_view ntupleName, std::string_view uri,
   const RNTupleReadOptions &options)
   : RPageSource(ntupleName, options)
   , fPageAllocator(std::make_unique<RPageAllocatorDaos>())
   , fPagePool(std::make_shared<RPagePool>())
   , fURI(uri)
   , fClusterPool(std::make_unique<RClusterPool>(*this))
{
   fDecompressor = std::make_unique<RNTupleDecompressor>();
   EnableDefaultMetrics("RPageSourceDaos");
 
   auto args = ParseDaosURI(uri);
   auto pool = std::make_shared<RDaosPool>(args.fPoolUuid, args.fSvcReplicas);
   fDaosContainer = std::make_unique<RDaosContainer>(pool, args.fContainerUuid);
}
 
 
ROOT::Experimental::Detail::RPageSourceDaos::~RPageSourceDaos() = default;
 
 
ROOT::Experimental::RNTupleDescriptor ROOT::Experimental::Detail::RPageSourceDaos::AttachImpl()
{
   RNTupleDescriptorBuilder descBuilder;
   RDaosNTupleAnchor ntpl;
   const auto ntplSize = RDaosNTupleAnchor::GetSize();
   auto buffer = std::make_unique<unsigned char[]>(ntplSize);
   fDaosContainer->ReadSingleAkey(buffer.get(), ntplSize, kOidAnchor, kDistributionKey,
                                  kAttributeKey, kCidMetadata);
   ntpl.Deserialize(buffer.get(), ntplSize).Unwrap();
 
   auto oclass = RDaosObject::ObjClassId(ntpl.fObjClass);
   if (oclass.IsUnknown())
      throw ROOT::Experimental::RException(R__FAIL("Unknown object class " + ntpl.fObjClass));
   fDaosContainer->SetDefaultObjectClass(oclass);
 
   descBuilder.SetOnDiskHeaderSize(ntpl.fNBytesHeader);
   buffer = std::make_unique<unsigned char[]>(ntpl.fLenHeader);
   auto zipBuffer = std::make_unique<unsigned char[]>(ntpl.fNBytesHeader);
   fDaosContainer->ReadSingleAkey(zipBuffer.get(), ntpl.fNBytesHeader, kOidHeader, kDistributionKey,
                                  kAttributeKey, kCidMetadata);
   fDecompressor->Unzip(zipBuffer.get(), ntpl.fNBytesHeader, ntpl.fLenHeader, buffer.get());
   Internal::RNTupleSerializer::DeserializeHeaderV1(buffer.get(), ntpl.fLenHeader, descBuilder);
 
   buffer = std::make_unique<unsigned char[]>(ntpl.fLenFooter);
   zipBuffer = std::make_unique<unsigned char[]>(ntpl.fNBytesFooter);
   fDaosContainer->ReadSingleAkey(zipBuffer.get(), ntpl.fNBytesFooter, kOidFooter, kDistributionKey,
                                  kAttributeKey, kCidMetadata);
   fDecompressor->Unzip(zipBuffer.get(), ntpl.fNBytesFooter, ntpl.fLenFooter, buffer.get());
   Internal::RNTupleSerializer::DeserializeFooterV1(buffer.get(), ntpl.fLenFooter, descBuilder);
 
   auto cg = descBuilder.GetClusterGroup(0);
   descBuilder.SetOnDiskFooterSize(ntpl.fNBytesFooter + cg.fPageListEnvelopeLink.fLocator.fBytesOnStorage);
   buffer = std::make_unique<unsigned char[]>(cg.fPageListEnvelopeLink.fUnzippedSize);
   zipBuffer = std::make_unique<unsigned char[]>(cg.fPageListEnvelopeLink.fLocator.fBytesOnStorage);
   fDaosContainer->ReadSingleAkey(
      zipBuffer.get(), cg.fPageListEnvelopeLink.fLocator.fBytesOnStorage,
      {static_cast<decltype(daos_obj_id_t::lo)>(cg.fPageListEnvelopeLink.fLocator.fPosition), 0}, kDistributionKey,
      kAttributeKey, kCidMetadata);
   fDecompressor->Unzip(zipBuffer.get(), cg.fPageListEnvelopeLink.fLocator.fBytesOnStorage,
                        cg.fPageListEnvelopeLink.fUnzippedSize, buffer.get());
 
   std::vector<RClusterDescriptorBuilder> clusters;
   Internal::RNTupleSerializer::DeserializePageListV1(buffer.get(), cg.fPageListEnvelopeLink.fUnzippedSize, clusters);
   for (std::size_t i = 0; i < clusters.size(); ++i) {
      descBuilder.AddCluster(i, std::move(clusters[i]));
   }
 
   return descBuilder.MoveDescriptor();
}
 
 
std::string ROOT::Experimental::Detail::RPageSourceDaos::GetObjectClass() const
{
   return fDaosContainer->GetDefaultObjectClass().ToString();
}
 
 
void ROOT::Experimental::Detail::RPageSourceDaos::LoadSealedPage(
   DescriptorId_t columnId, const RClusterIndex &clusterIndex, RSealedPage &sealedPage)
{
   const auto clusterId = clusterIndex.GetClusterId();
   const auto &clusterDescriptor = fDescriptor.GetClusterDescriptor(clusterId);
 
   auto pageInfo = clusterDescriptor.GetPageRange(columnId).Find(clusterIndex.GetIndex());
 
   const auto bytesOnStorage = pageInfo.fLocator.fBytesOnStorage;
   sealedPage.fSize = bytesOnStorage;
   sealedPage.fNElements = pageInfo.fNElements;
   if (sealedPage.fBuffer) {
      fDaosContainer->ReadSingleAkey(const_cast<void *>(sealedPage.fBuffer), bytesOnStorage,
                                     {static_cast<decltype(daos_obj_id_t::lo)>(pageInfo.fLocator.fPosition), 0},
                                     kDistributionKey, kAttributeKey);
   }
}
 
ROOT::Experimental::Detail::RPage ROOT::Experimental::Detail::RPageSourceDaos::PopulatePageFromCluster(
   ColumnHandle_t columnHandle, const RClusterDescriptor &clusterDescriptor, ClusterSize_t::ValueType idxInCluster)
{
   const auto columnId = columnHandle.fId;
   const auto clusterId = clusterDescriptor.GetId();
 
   auto pageInfo = clusterDescriptor.GetPageRange(columnId).Find(idxInCluster);
 
   const auto element = columnHandle.fColumn->GetElement();
   const auto elementSize = element->GetSize();
   const auto bytesOnStorage = pageInfo.fLocator.fBytesOnStorage;
 
   const void *sealedPageBuffer = nullptr; // points either to directReadBuffer or to a read-only page in the cluster
   std::unique_ptr<unsigned char []> directReadBuffer; // only used if cluster pool is turned off
 
   if (fOptions.GetClusterCache() == RNTupleReadOptions::EClusterCache::kOff) {
      directReadBuffer = std::make_unique<unsigned char[]>(bytesOnStorage);
      fDaosContainer->ReadSingleAkey(directReadBuffer.get(), bytesOnStorage,
                                     {static_cast<decltype(daos_obj_id_t::lo)>(pageInfo.fLocator.fPosition), 0},
                                     kDistributionKey, kAttributeKey);
      fCounters->fNPageLoaded.Inc();
      fCounters->fNRead.Inc();
      fCounters->fSzReadPayload.Add(bytesOnStorage);
      sealedPageBuffer = directReadBuffer.get();
   } else {
      if (!fCurrentCluster || (fCurrentCluster->GetId() != clusterId) || !fCurrentCluster->ContainsColumn(columnId))
         fCurrentCluster = fClusterPool->GetCluster(clusterId, fActiveColumns);
      R__ASSERT(fCurrentCluster->ContainsColumn(columnId));
 
      auto cachedPage = fPagePool->GetPage(columnId, RClusterIndex(clusterId, idxInCluster));
      if (!cachedPage.IsNull())
         return cachedPage;
 
      ROnDiskPage::Key key(columnId, pageInfo.fPageNo);
      auto onDiskPage = fCurrentCluster->GetOnDiskPage(key);
      R__ASSERT(onDiskPage && (bytesOnStorage == onDiskPage->GetSize()));
      sealedPageBuffer = onDiskPage->GetAddress();
   }
 
   std::unique_ptr<unsigned char []> pageBuffer;
   {
      RNTupleAtomicTimer timer(fCounters->fTimeWallUnzip, fCounters->fTimeCpuUnzip);
      pageBuffer = UnsealPage({sealedPageBuffer, bytesOnStorage, pageInfo.fNElements}, *element);
      fCounters->fSzUnzip.Add(elementSize * pageInfo.fNElements);
   }
 
   const auto indexOffset = clusterDescriptor.GetColumnRange(columnId).fFirstElementIndex;
   auto newPage = fPageAllocator->NewPage(columnId, pageBuffer.release(), elementSize, pageInfo.fNElements);
   newPage.SetWindow(indexOffset + pageInfo.fFirstInPage, RPage::RClusterInfo(clusterId, indexOffset));
   fPagePool->RegisterPage(newPage,
      RPageDeleter([](const RPage &page, void * /*userData*/)
      {
         RPageAllocatorDaos::DeletePage(page);
      }, nullptr));
   fCounters->fNPagePopulated.Inc();
   return newPage;
}
 
 
ROOT::Experimental::Detail::RPage ROOT::Experimental::Detail::RPageSourceDaos::PopulatePage(
   ColumnHandle_t columnHandle, NTupleSize_t globalIndex)
{
   const auto columnId = columnHandle.fId;
   auto cachedPage = fPagePool->GetPage(columnId, globalIndex);
   if (!cachedPage.IsNull())
      return cachedPage;
 
   const auto clusterId = fDescriptor.FindClusterId(columnId, globalIndex);
   R__ASSERT(clusterId != kInvalidDescriptorId);
   const auto &clusterDescriptor = fDescriptor.GetClusterDescriptor(clusterId);
   const auto selfOffset = clusterDescriptor.GetColumnRange(columnId).fFirstElementIndex;
   R__ASSERT(selfOffset <= globalIndex);
   return PopulatePageFromCluster(columnHandle, clusterDescriptor, globalIndex - selfOffset);
}
 
 
ROOT::Experimental::Detail::RPage ROOT::Experimental::Detail::RPageSourceDaos::PopulatePage(
   ColumnHandle_t columnHandle, const RClusterIndex &clusterIndex)
{
   const auto clusterId = clusterIndex.GetClusterId();
   const auto idxInCluster = clusterIndex.GetIndex();
   const auto columnId = columnHandle.fId;
   auto cachedPage = fPagePool->GetPage(columnId, clusterIndex);
   if (!cachedPage.IsNull())
      return cachedPage;
 
   R__ASSERT(clusterId != kInvalidDescriptorId);
   const auto &clusterDescriptor = fDescriptor.GetClusterDescriptor(clusterId);
   return PopulatePageFromCluster(columnHandle, clusterDescriptor, idxInCluster);
}
 
void ROOT::Experimental::Detail::RPageSourceDaos::ReleasePage(RPage &page)
{
   fPagePool->ReturnPage(page);
}
 
std::unique_ptr<ROOT::Experimental::Detail::RPageSource> ROOT::Experimental::Detail::RPageSourceDaos::Clone() const
{
   auto clone = new RPageSourceDaos(fNTupleName, fURI, fOptions);
   return std::unique_ptr<RPageSourceDaos>(clone);
}
 
std::vector<std::unique_ptr<ROOT::Experimental::Detail::RCluster>>
ROOT::Experimental::Detail::RPageSourceDaos::LoadClusters(std::span<RCluster::RKey> clusterKeys)
{
   std::vector<std::unique_ptr<ROOT::Experimental::Detail::RCluster>> result;
   for (const auto &clusterKey : clusterKeys) {
      auto clusterId = clusterKey.fClusterId;
      fCounters->fNClusterLoaded.Inc();
 
      const auto &clusterDesc = GetDescriptor().GetClusterDescriptor(clusterId);
 
      struct RDaosSealedPageLocator {
         RDaosSealedPageLocator() = default;
         RDaosSealedPageLocator(DescriptorId_t c, NTupleSize_t p, std::uint64_t o, std::uint64_t s, std::size_t b)
            : fColumnId(c), fPageNo(p), fObjectId(o), fSize(s), fBufPos(b) {}
         DescriptorId_t fColumnId = 0;
         NTupleSize_t fPageNo = 0;
         std::uint64_t fObjectId = 0;
         std::uint64_t fSize = 0;
         std::size_t fBufPos = 0;
      };
 
      // Collect the page necessary page meta-data and sum up the total size of the compressed and packed pages
      std::vector<RDaosSealedPageLocator> onDiskPages;
      std::size_t szPayload = 0;
      for (auto columnId : clusterKey.fColumnSet) {
         const auto &pageRange = clusterDesc.GetPageRange(columnId);
         NTupleSize_t pageNo = 0;
         for (const auto &pageInfo : pageRange.fPageInfos) {
            const auto &pageLocator = pageInfo.fLocator;
            onDiskPages.emplace_back(RDaosSealedPageLocator(
               columnId, pageNo, pageLocator.fPosition, pageLocator.fBytesOnStorage, szPayload));
            szPayload += pageLocator.fBytesOnStorage;
            ++pageNo;
         }
      }
 
      // Prepare the input vector for the RDaosContainer::ReadV() call
      std::vector<RDaosContainer::RWOperation> readRequests;
      auto buffer = new unsigned char[szPayload];
      for (auto &s : onDiskPages) {
         std::vector<d_iov_t> iovs(1);
         d_iov_set(&iovs[0], buffer + s.fBufPos, s.fSize);
         readRequests.emplace_back(daos_obj_id_t{s.fObjectId, 0},
                                   kDistributionKey, kAttributeKey, iovs);
      }
      fCounters->fSzReadPayload.Add(szPayload);
 
      // Register the on disk pages in a page map
      auto pageMap = std::make_unique<ROnDiskPageMapHeap>(std::unique_ptr<unsigned char []>(buffer));
      for (const auto &s : onDiskPages) {
         ROnDiskPage::Key key(s.fColumnId, s.fPageNo);
         pageMap->Register(key, ROnDiskPage(buffer + s.fBufPos, s.fSize));
      }
      fCounters->fNPageLoaded.Add(onDiskPages.size());
 
      {
         RNTupleAtomicTimer timer(fCounters->fTimeWallRead, fCounters->fTimeCpuRead);
         fDaosContainer->ReadV(readRequests);
      }
      fCounters->fNReadV.Inc();
      fCounters->fNRead.Add(readRequests.size());
 
      auto cluster = std::make_unique<RCluster>(clusterId);
      cluster->Adopt(std::move(pageMap));
      for (auto colId : clusterKey.fColumnSet)
         cluster->SetColumnAvailable(colId);
 
      result.emplace_back(std::move(cluster));
   }
   return result;
}
 
 
void ROOT::Experimental::Detail::RPageSourceDaos::UnzipClusterImpl(RCluster *cluster)
{
   RNTupleAtomicTimer timer(fCounters->fTimeWallUnzip, fCounters->fTimeCpuUnzip);
   fTaskScheduler->Reset();
 
   const auto clusterId = cluster->GetId();
   const auto &clusterDescriptor = fDescriptor.GetClusterDescriptor(clusterId);
 
   std::vector<std::unique_ptr<RColumnElementBase>> allElements;
 
   const auto &columnsInCluster = cluster->GetAvailColumns();
   for (const auto columnId : columnsInCluster) {
      const auto &columnDesc = fDescriptor.GetColumnDescriptor(columnId);
 
      allElements.emplace_back(RColumnElementBase::Generate(columnDesc.GetModel().GetType()));
 
      const auto &pageRange = clusterDescriptor.GetPageRange(columnId);
      std::uint64_t pageNo = 0;
      std::uint64_t firstInPage = 0;
      for (const auto &pi : pageRange.fPageInfos) {
         ROnDiskPage::Key key(columnId, pageNo);
         auto onDiskPage = cluster->GetOnDiskPage(key);
         R__ASSERT(onDiskPage && (onDiskPage->GetSize() == pi.fLocator.fBytesOnStorage));
 
         auto taskFunc =
            [this, columnId, clusterId, firstInPage, onDiskPage,
             element = allElements.back().get(),
             nElements = pi.fNElements,
             indexOffset = clusterDescriptor.GetColumnRange(columnId).fFirstElementIndex
            ] () {
               auto pageBuffer = UnsealPage({onDiskPage->GetAddress(), onDiskPage->GetSize(), nElements}, *element);
               fCounters->fSzUnzip.Add(element->GetSize() * nElements);
 
               auto newPage = fPageAllocator->NewPage(columnId, pageBuffer.release(), element->GetSize(), nElements);
               newPage.SetWindow(indexOffset + firstInPage, RPage::RClusterInfo(clusterId, indexOffset));
               fPagePool->PreloadPage(newPage,
                  RPageDeleter([](const RPage &page, void * /*userData*/)
                  {
                     RPageAllocatorDaos::DeletePage(page);
                  }, nullptr));
            };
 
         fTaskScheduler->AddTask(taskFunc);
 
         firstInPage += pi.fNElements;
         pageNo++;
      } // for all pages in column
   } // for all columns in cluster
 
   fCounters->fNPagePopulated.Add(cluster->GetNOnDiskPages());
 
   fTaskScheduler->Wait();
}