pitrou commented on code in PR #14100:
URL: https://github.com/apache/arrow/pull/14100#discussion_r970950406
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cpp/src/arrow/json/parser.cc:
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@@ -749,9 +746,16 @@ class HandlerBase : public BlockParser,
/// there is no field with that name
bool SetFieldBuilder(string_view key, bool* duplicate_keys) {
auto parent = Cast<Kind::kObject>(builder_stack_.back());
- field_index_ = parent->GetFieldIndex(std::string(key));
- if (ARROW_PREDICT_FALSE(field_index_ == -1)) {
- return false;
+ DCHECK(field_index_ >= -1 && field_index_ < parent->num_fields());
+ // Predict that this field is known and immediately follows the last one.
Otherwise,
+ // fall back to the hash table lookup
+ ++field_index_;
+ if (ARROW_PREDICT_FALSE(field_index_ == parent->num_fields() ||
+ key != parent->field_name(field_index_))) {
+ field_index_ = parent->GetFieldIndex(std::string(key));
Review Comment:
Note that a separate optimization would be to avoid creating a new
`std::string` when looking up the field index (for example by having a separate
vector of field names and using a `std::unordered_map<string_view, int>` for
the actual lookup).
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