[IMPALA-10323] use snprintf instead of lexical_cast when casting int to string, to improve multi-thread performance

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: Impala 3.1.0, Impala 3.2.0, Impala 3.3.0, Impala 3.4.0
• Fix Version/s: Impala 4.0.0
• Component/s: Backend
• Environment: 3 nodes ( 24 core, 64 GB mem) ; impala 3.4
• Epic Color: ghx-label-3
• Assignee: wesleydeng
• Reporter: wesleydeng
• Created: 12/Nov/20 12:51
• Updated: 10/Jun/21 13:11
• Resolved: 10/Jun/21 13:11

Description

For float_type, lexical_cast is replace by snprintf （issue https://issues.apache.org/jira/browse/IMPALA-1738），but why not do the same replacement for num_type.

Test is done in 2 sql case :

1)  group by cast int to string : 

select cast(f1 as string) as kk, count ( * ) from test.my_table group by kk;

2) group by int : 

select f1 as kk, count( *  ) from test.my_table  group by kk;

from the benchmark, we can see that performance decreased seriously with more thread.

But using snprintf, performance improved significantly with more thread .