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https://issues.apache.org/jira/browse/ARROW-1712?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16332605#comment-16332605
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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_r162685206
 
 

 ##########
 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));
+  
+  ASSERT_EQ(builder_->length(), length);
 
 Review comment:
   In googletest, the 1st parameter passed to `ASSERT_EQ` should be the 
expected result, so flip the argument order here and below

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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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