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[ntuple] Add partioning to RNTupleJoinTable
#17919
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Test Results 20 files 20 suites 4d 23h 29m 30s ⏱️ For more details on these failures, see this check. Results for commit 3a3fa99. ♻️ This comment has been updated with latest results. |
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Nice improvement! Some minor comments for now
RCombinedJoinFieldValue(const std::vector<NTupleJoinFieldValue_t> &fieldValues) | ||
{ | ||
fFieldValues.reserve(fieldValues.size()); | ||
fFieldValues = fieldValues; | ||
} |
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Shouldn't this be equivalent?
RCombinedJoinFieldValue(const std::vector<NTupleJoinFieldValue_t> &fieldValues) | |
{ | |
fFieldValues.reserve(fieldValues.size()); | |
fFieldValues = fieldValues; | |
} | |
RCombinedJoinFieldValue(const std::vector<NTupleJoinFieldValue_t> &fieldValues): fFieldValues(fieldValues) | |
{ | |
} |
class RCombinedJoinFieldValue { | ||
public: |
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Maybe struct
better represents the class layout in this case?
/// https://www.boost.org/doc/libs/1_55_0/doc/html/hash/reference.html#boost.hash_combine). | ||
struct RCombinedJoinFieldValueHash { | ||
inline std::size_t operator()(const RCombinedJoinFieldValue &joinFieldValue) const | ||
/// The mapping itself. Maps field values (or combinations thereof in case the join key is a composed of multiple |
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/// The mapping itself. Maps field values (or combinations thereof in case the join key is a composed of multiple | |
/// The mapping itself. Maps field values (or combinations thereof in case the join key is composed of multiple |
switch (*run) { | ||
// For run == 0, no entry indexes are expected because they were added using the default partition key | ||
case 0: EXPECT_EQ(entryIdxs.size(), 0ul); break; | ||
// For run == 0, we expect exactly one entry index |
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// For run == 0, we expect exactly one entry index | |
// For run == 1, we expect exactly one entry index |
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A couple of minor comments
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I left many comments. The answer to some of them may well be that it's motivated by future changes. In that case please feel free to simply resolve the thread(s).
/// \return The entry numbers that correspond to `valuePtrs`. When there are no corresponding entries, an empty | ||
/// vector is returned. | ||
std::vector<ROOT::NTupleSize_t> GetEntryIndexes(const std::vector<void *> &valuePtrs) const | ||
{ | ||
return GetEntryIndexes(valuePtrs, fPartitionKeys); | ||
} |
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Is this useful in case of multiple partitions since the return value loses the information which mapping the indexes are relative to? Maybe what we want instead is GetEntryIndexes(const std::vector<void *> &valuePtrs, PartitionKey_t partitionKey = kDefaultPartitionKey)
?
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The issue I see with that interface is that it may give false negatives when there are mappings in partitions other than the default. I think it's okay to lose information here, if one needs this information they should instead use (GetEntryIndexes(const std::vector<void *> &valuePtrs, PartitionKey_t partitionKey)
to be able to track the partitions.
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Yes, I now realize that the information is equally lost for GetEntryIndexes(const std::vector<void *> &valuePtrs, const std::vector<PartitionKey_t> &partitionKeys)
. I'm still not sure how useful this is (at the moment) since a mapping spans an entire page source, but I guess this will change in the future.
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@@ -35,57 +35,98 @@ namespace Internal { | |||
// clang-format on | |||
class RNTupleJoinTable { | |||
public: | |||
using NTupleJoinValue_t = std::uint64_t; | |||
using JoinValue_T = std::uint64_t; |
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using JoinValue_T = std::uint64_t; | |
using JoinValue_t = std::uint64_t; |
(that's what the commit message says...)
/// \return The entry numbers that correspond to `valuePtrs`. When there are no corresponding entries, an empty | ||
/// vector is returned. | ||
std::vector<ROOT::NTupleSize_t> GetEntryIndexes(const std::vector<void *> &valuePtrs) const | ||
{ | ||
return GetEntryIndexes(valuePtrs, fPartitionKeys); | ||
} |
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Yes, I now realize that the information is equally lost for GetEntryIndexes(const std::vector<void *> &valuePtrs, const std::vector<PartitionKey_t> &partitionKeys)
. I'm still not sure how useful this is (at the moment) since a mapping spans an entire page source, but I guess this will change in the future.
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LGTM in principle, thanks for making all the changes. I have one final question about the semantics of GetPartitionedEntryIndexes
, and what it should return in case there is no index in a partition.
auto entriesForPartition = GetEntryIndexes(valuePtrs, partitionKey); | ||
entryIdxs[partitionKey].insert(entryIdxs[partitionKey].end(), entriesForPartition.begin(), | ||
entriesForPartition.end()); |
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Should this check
auto entriesForPartition = GetEntryIndexes(valuePtrs, partitionKey); | |
entryIdxs[partitionKey].insert(entryIdxs[partitionKey].end(), entriesForPartition.begin(), | |
entriesForPartition.end()); | |
auto entriesForPartition = GetEntryIndexes(valuePtrs, partitionKey); | |
if (!entriesForPartition.empty()) | |
entryIdxs[partitionKey].insert(entryIdxs[partitionKey].end(), entriesForPartition.begin(), | |
entriesForPartition.end()); |
? The question is what do we want to return if there is no index in a particular partition: an empty vector
or omit the key from the map. The other overload seems to do the latter, and that's also what I would semantically expect. (we should probably add a test for this overload, if I'm not mistaken)
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Oh yeah, thanks for catching this! I think for now indeed it's fine to use the latter behavior and let time and future developments tell whether whether this was the right intuition. I've expanded the tests as well.
With this addition, the join table can be split up into several mappings from join values to entry numbers, according to some (numeric) partition key. It has several use cases, but the immediate one is that with this approach, the join table is not restricted to one page source anymore. This is useful for the integration into the `RNTupleProcessor`, where we want to be able to create joins of chains of RNTuples and have to deal with more than one page source. As a side-effect, the state management of the join table and the notion of lazy building has changed. There is no single `isBuilt` state anymore, and the `Add` function eagerly builds the mapping for the provided page source and adds it to the join table. As such, the responsibility of deciding whether to eagerly or lazily build the join table is moved to the application using the join table (i.e. by strategically calling `Add`).
Since it is declared within `RNTupleJoinTable`, it is clear that this type belongs to RNTuple from the context.
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With this addition, the
RNTupleJoinTable
can be split up into several mappings from join values to entry numbers, according to some (numeric) partition key. Using a partition key is optional; a default partition key is used when none has been specified by the user.The
RNTupleJoinTable
now has an inner class,REntryMapping
, which in practice now represents what theRNTupleJoinTable
represented previously, i.e., a mapping from join field values to entry numbers:The join table itself now instead provides a mapping from partition keys to (a collection of) these entry mappings:
The reason one partition can contain multiple entry mappings is twofold:
The most immediate use case of the partitioning approach added in this PR, is that this way, the
RNTupleJoinTable
itself is not restricted to one page source anymore (this restriction is now inREntryMapping
instead). This is useful for the integration into theRNTupleProcessor
, where we want to be able to create joins of chains of RNTuples and have to deal with more than one page source (see also #17132).As a side-effect, the state management of the join table and the notion of lazy building has changed. There is no single
isBuilt
state anymore, and theAdd
function eagerly builds the mapping for the provided page source and adds it to the join table. As such, the responsibility of deciding whether to eagerly or lazily build the join table is moved to the application using the join table (i.e. by strategically callingAdd
).