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https://issues.apache.org/jira/browse/ARROW-1712?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16332606#comment-16332606
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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_r162685684
##########
File path: cpp/src/arrow/array-test.cc
##########
@@ -1154,6 +1154,54 @@ TEST_F(TestBinaryBuilder, TestScalarAppend) {
}
}
}
+
+TEST_F(TestBinaryBuilder, TestCapacityReserve) {
+ vector<string> strings = {"a", "bb", "cc", "ddddd", "eeeee"};
+ int64_t N = static_cast<int>(strings.size());
+ int64_t length = 0;
+ int64_t data_length = 0;
+ int64_t capacity = N;
+
+ ASSERT_OK(builder_->Reserve(capacity));
+ ASSERT_OK(builder_->ReserveData(capacity));
Review comment:
These reservations should be viewed as different, because the size of the
offsets buffer and the data buffer grow at different rates. The way this unit
test should read is:
* Call `ReserveData` with enough space for some large-ish amount of data
(say 4K bytes or so)
* Append <= N bytes incrementally
* Check that the capacity remains invariant at the end (i.e. the initial
`ReserveData` made sure that no additional reallocations took place)
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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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