[Sequoia database Sequoiadb] [consultation] [] [RC] RC transaction isolation level, the execution count mysql dirty read happens

Detailed Description] [Problems
SequoiaDB open transaction, transaction level, RC, execution count occurs in the case of a dirty read Mysql, do the following:
1. Open the transaction isolation level of the RC;
2. execution count SELECT ( ) Get the number of records from X1;
3. the recording is inserted again;
4. step 2 again;
step 4 found count number of records returned newly inserted, dirty read problem.
Details are at Annex mysql-1/2/3 / 4.png
[solutions]
1. The current version (v3.2.1) of the quick count mechanism is really dirty reads, but quickly return results for the interim count unconditionally.
2. The current special quick count is opened by sequoiadb_optimize_select_count optimized parameters, system parameters can be hidden by: sequoiadb_optimize_select_count: to switch.
[Configuration] Method
1. nonpersistent manner commencement
mysql> set global sequoiadb_optimizer_select_count = OFF;
restart mysql reset to the default parameter value ON.
2, effective after persistent
modify database / <Examples> /auto.cnf profile, arranged in sequoiadb_optimizer_select_count = OFF [mysqld] module performing bin / sdb_sql_ctl restart <instance name> restart the instance after the changes.
[Note]
1. select count with a filter condition ( ) from the Table the WHERE ... statement or the original performance, because under pressure to the storage engine mysql will not count.
2. sdb the count () interface is a direct access to the counter, the equivalent of dirty read. If you care, you can not open sequoiadb_optimize_select_count.
3.sequoiadb_optimizer_select_count hidden parameters are internal parameters, not open, no relevant information on.