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https://issues.apache.org/jira/browse/ARROW-1712?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16329357#comment-16329357
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ASF GitHub Bot commented on ARROW-1712:
---------------------------------------
wesm commented on a change in pull request #1481: ARROW-1712: [C++] Add method
to BinaryBuilder to reserve space for value data
URL: https://github.com/apache/arrow/pull/1481#discussion_r162163169
##########
File path: cpp/src/arrow/builder.cc
##########
@@ -1222,9 +1222,14 @@ Status BinaryBuilder::Init(int64_t elements) {
Status BinaryBuilder::Resize(int64_t capacity) {
DCHECK_LT(capacity, std::numeric_limits<int32_t>::max());
// one more then requested for offsets
- RETURN_NOT_OK(offsets_builder_.Resize((capacity + 1) * sizeof(int64_t)));
+ RETURN_NOT_OK(offsets_builder_.Resize((capacity + 1) * sizeof(int32_t)));
return ArrayBuilder::Resize(capacity);
}
+
+Status BinaryBuilder::ReserveData(int64_t capacity) {
+ DCHECK_LT(capacity, std::numeric_limits<int32_t>::max());
+ return value_data_builder_.Resize(capacity * sizeof(int64_t));
Review comment:
I think this should be `Resize(capacity + value_data_builder_.length())`.
The `sizeof(int64_t)` looks like a copy-paste error from implementation of
`BinaryBuilder::Resize` above (and that should be `sizeof(int32_t)` there, so
we should fix that)
We should check that `extra_capacity + length` does not exceed INT32_MAX but
probably return `Status::Invalid` since overflowing a `BinaryBuilder` is likely
to happen somewhat more regularly
I note also that `BufferBuilder` and `TypedBufferBuilder<T>` don't have a
`shrink_to_fit` option in their `Resize` method, that would be good to add to
avoid unnecessary reallocations
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> [C++] Add method to BinaryBuilder to reserve space for value data
> -----------------------------------------------------------------
>
> Key: ARROW-1712
> URL: https://issues.apache.org/jira/browse/ARROW-1712
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C++
> Reporter: Wes McKinney
> Assignee: Panchen Xue
> Priority: Major
> Labels: pull-request-available
> Fix For: 0.9.0
>
>
> The {{Resize}} and {{Reserve}} methods only reserve space for the value
> offsets. When building binary/string arrays with a known size (or some
> reasonable estimate), it would be more efficient to reserve once at the
> beginning to prevent internal reallocations
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