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From:Xuekun Hu Date:July 15 2009 12:59pm
Subject:Re: why REPEATABLE-READ read more innodb rows than READ-COMMITTED
during DBT2 run?
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does anyone has ideas? :-)

On Tue, Jul 14, 2009 at 2:02 PM, Xuekun Hu<xuekun.hu@stripped> wrote:
> Hi, Guys
>
> I set transaction isolation level to REPEATABLE-READ and
> READ-COMMITTED separately to test DBT2 10 warehouses on 16 cores
> system with 32 connections. The dbt2 performance with REPEATABLE-READ
> was 9% lower than with READ-COMMITTED. By checking status, I found the
> REPEATABLE-READ mode was reading 64% more "innodb_rows_read" than
> READ-COMMITTED mode.
>
> DBT2-10WH, Normalized to one NOTPM
> REPEATABLE-READ
>        Innodb_rows_deleted          
>                   5.78
>        Innodb_rows_inserted          
>                  134.14
>        Innodb_rows_read            
>                    25693.97
>        Innodb_rows_updated          
>                   253.05
>        Queries              
>                          
> 640.23
> READ-COMMITTED
>        Innodb_rows_deleted          
>                   8.46
>        Innodb_rows_inserted          
>                  134.22
>        Innodb_rows_read            
>                    15699.77
>        Innodb_rows_updated          
>                   252.18
>        Queries              
>                          
> 640.45
>
> From my understanding, "innodb_rows_read" is counting the number of
> rows read from InnoDB tables. Here the "row" should refer to the
> physical one, instead of snapshot one. That means if two concurrent
> transactions were updating a same row, two record versions were
> created. However when another consistent read read this row, the
> counter "innodb_rows_read" will be added by 1, not 2 or 3.
>
> So why REPEATABLE-READ read more innodb rows than READ-COMMITTED? Your
> comments are appreciated.
>
> Thx, Xuekun
>
Thread
why REPEATABLE-READ read more innodb rows than READ-COMMITTED during DBT2 run?Xuekun Hu14 Jul
  • Re: why REPEATABLE-READ read more innodb rows than READ-COMMITTED during DBT2 run?Xuekun Hu15 Jul
  • Re: why REPEATABLE-READ read more innodb rows than READ-COMMITTEDduring DBT2 run?Guilhem Bichot29 Jul
    • Re: why REPEATABLE-READ read more innodb rows than READ-COMMITTED during DBT2 run?Xuekun Hu30 Jul