pitrou commented on a change in pull request #8050:
URL: https://github.com/apache/arrow/pull/8050#discussion_r482853096
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File path: cpp/src/arrow/ipc/dictionary.cc
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@@ -143,10 +143,43 @@ int DictionaryFieldMapper::num_fields() const { return
impl_->num_fields(); }
// DictionaryMemo implementation
struct DictionaryMemo::Impl {
- // Map of dictionary id to dictionary array
- std::unordered_map<int64_t, std::shared_ptr<ArrayData>> id_to_dictionary_;
+ // Map of dictionary id to dictionary array(s) (several in case of deltas)
+ std::unordered_map<int64_t, ArrayDataVector> id_to_dictionary_;
std::unordered_map<int64_t, std::shared_ptr<DataType>> id_to_type_;
DictionaryFieldMapper mapper_;
+
+ Result<decltype(id_to_dictionary_)::iterator> FindDictionary(int64_t id) {
+ auto it = id_to_dictionary_.find(id);
+ if (it == id_to_dictionary_.end()) {
+ return Status::KeyError("Dictionary with id ", id, " not found");
+ }
+ return it;
+ }
+
+ Result<std::shared_ptr<ArrayData>> ReifyDictionary(int64_t id, MemoryPool*
pool) {
+ ARROW_ASSIGN_OR_RAISE(auto it, FindDictionary(id));
+ ArrayDataVector* data_vector = &it->second;
+
+ DCHECK(!data_vector->empty());
+ if (data_vector->size() > 1) {
+ // There are deltas, we need to concatenate them to the first dictionary.
+ ArrayVector to_combine;
+ to_combine.reserve(data_vector->size());
+ // IMPORTANT: At this point, the dictionary data may be untrusted.
+ // We need to validate it, as concatenation can crash on invalid or
+ // corrupted data. Full validation is necessary for certain types
+ // (for example nested dictionaries).
+ // XXX: this won't work if there are unresolved nested dictionaries.
Review comment:
Ideally yes, but our current infrastructure doesn't make this very easy.
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