bkietz commented on a change in pull request #9670:
URL: https://github.com/apache/arrow/pull/9670#discussion_r591894657
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File path: cpp/src/arrow/dataset/file_base.cc
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@@ -137,16 +132,174 @@ std::string FileSystemDataset::ToString() const {
return repr;
}
-Result<FragmentIterator> FileSystemDataset::GetFragmentsImpl(Expression
predicate) {
- FragmentVector fragments;
+namespace {
- for (const auto& fragment : fragments_) {
- ARROW_ASSIGN_OR_RAISE(
- auto simplified,
- SimplifyWithGuarantee(predicate, fragment->partition_expression()));
- if (simplified.IsSatisfiable()) {
- fragments.push_back(fragment);
+// Helper class for efficiently detecting subtrees given fragment partition
expressions.
+// Partition expressions are broken into conjunction members and each member
dictionary
+// encoded to impose a sortable ordering. In addition, subtrees are generated
which span
+// groups of fragments and nested subtrees. After encoding each fragment is
guaranteed to
+// be a descendant of at least one subtree. For example, given fragments in a
+// HivePartitioning with paths:
+//
+// /num=0/al=eh/dat.par
+// /num=0/al=be/dat.par
+// /num=1/al=eh/dat.par
+// /num=1/al=be/dat.par
+//
+// The following subtrees will be introduced:
+//
+// /num=0/
+// /num=0/al=eh/
+// /num=0/al=eh/dat.par
+// /num=0/al=be/
+// /num=0/al=be/dat.par
+// /num=1/
+// /num=1/al=eh/
+// /num=1/al=eh/dat.par
+// /num=1/al=be/
+// /num=1/al=be/dat.par
+struct SubtreeImpl {
+ using expression_code = char32_t;
Review comment:
Also: basic_string has the short string approximation in most standard
libraries (so a string with as many as 4 `expression_code`s will probably be
stored without allocation) and supports hashing out of the box
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