Hi, Aleksey!

On Mar 26, Aleksey Midenkov wrote:
> revision-id: 74b2eba1ca6 (mariadb-10.3.12-115-g74b2eba1ca6)
> parent(s): 2c0901d808b
> author: Aleksey Midenkov <mide...@gmail.com>
> committer: Sergei Golubchik <s...@mariadb.com>
> timestamp: 2019-03-26 17:43:38 +0100
> message:
> 
> MDEV-15458 Segfault in heap_scan() upon UPDATE after ADD SYSTEM VERSIONING
> 
> * HA_EXTRA_REMEMBER_POS, HA_EXTRA_RESTORE_POS for HEAP storage engine
> * Versioning tests support
> 
> diff --git a/sql/sql_insert.cc b/sql/sql_insert.cc
> index abe4254db3e..1d51947cc86 100644
> --- a/sql/sql_insert.cc
> +++ b/sql/sql_insert.cc
> @@ -1643,7 +1643,12 @@ int vers_insert_history_row(TABLE *table)
>    if (row_start->cmp(row_start->ptr, row_end->ptr) >= 0)
>      return 0;
>  
> -  return table->file->ha_write_row(table->record[0]);
> +  int res;
> +  if ((res= table->file->extra(HA_EXTRA_REMEMBER_POS)))
> +    return res;
> +  if ((res= table->file->ha_write_row(table->record[0])))
> +    return res;
> +  return table->file->extra(HA_EXTRA_RESTORE_POS);
>  }

Frankly, I don't like it. I mean, this particular fix is fine, but
here's the problem:

We now have (at least) three features where the server might need to do
something (insert/update/search) during the index/rnd scan.

And three different solutions: you use HA_EXTRA_REMEMBER_POS in system
versioning, Nikita simply sets delete_while_scanning=false in
application time period tables, and Sachin uses handler::clone() to
create a second handler that can be used to check for hash collisions
without disrupting the scan on the primary handler.

I think it's getting somewhat out of hands. Can we please reduce the
number of approaches to fix the same issue?

Regards,
Sergei
Chief Architect MariaDB
and secur...@mariadb.org

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