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https://issues.apache.org/jira/browse/IMPALA-12373?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17788946#comment-17788946
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ASF subversion and git services commented on IMPALA-12373:
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Commit 6d3317b9a11c858f412337e44b207548498d8b4f in impala's branch
refs/heads/master from Daniel Becker
[ https://gitbox.apache.org/repos/asf?p=impala.git;h=6d3317b9a ]
IMPALA-12570: Add longer strings to tables containing collections
IMPALA-12373 introduces small string optimisation, after which not all
strings will have a var-len part.
IMPALA-12159 adds support for ORDER BY for collections of variable
length types in the select list, but the test tables it uses only/mostly
contain short strings.
This patch has two modifications:
1. It introduces longer strings in 'collection_tbl' and
'collection_struct_mix'. It also adds two more rows to the existing one
in 'collection_tbl' so that it can be used in sorting tests. These
tables are only used by complex types tests, so the impact is limited.
2. It modifies RandomNestedDataGenerator.java, so that now it takes a
parameter for string length. Some variable names are changed to clearer
names. The references to and uses of RandomNestedDataGenerator are
updated.
Change-Id: Ief770d6bc9258fce159a733d5afa34fe594b96f8
Reviewed-on: http://gerrit.cloudera.org:8080/20718
Reviewed-by: Impala Public Jenkins <impala-public-jenk...@cloudera.com>
Tested-by: Impala Public Jenkins <impala-public-jenk...@cloudera.com>
> Implement Small String Optimization for StringValue
> ---------------------------------------------------
>
> Key: IMPALA-12373
> URL: https://issues.apache.org/jira/browse/IMPALA-12373
> Project: IMPALA
> Issue Type: Improvement
> Reporter: Zoltán Borók-Nagy
> Assignee: Zoltán Borók-Nagy
> Priority: Major
> Labels: Performance
> Attachments: small_string.cpp
>
>
> Implement Small String Optimization for StringValue.
> Current memory layout of StringValue is:
> {noformat}
> char* ptr; // 8 byte
> int len; // 4 byte
> {noformat}
> For small strings with size up to 8 we could store the string contents in the
> bytes of the 'ptr'. Something like that:
> {noformat}
> union {
> char* ptr;
> char small_buf[sizeof(ptr)];
> };
> int len;
> {noformat}
> Many C++ string implementations use the {{Small String Optimization}} to
> speed up work with small strings. For example:
> {code:java}
> Microsoft STL, libstdc++, libc++, Boost, Folly.{code}
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