In MariaDB, we have a confusing problem where:
* The transaction_isolation option can be set in a configuration file, but it cannot be set dynamically.
* The tx_isolation system variable can be set dynamically, but it cannot be set in a configuration file.
Therefore, we have two different names for the same thing in different contexts. This is needlessly confusing, and it complicates the documentation. The same thing applys for transaction_read_only.
MySQL 5.7 solved this problem by making them into system variables. https://dev.mysql.com/doc/relnotes/mysql/5.7/en/news-5-7-20.html
This commit takes a similar approach by adding new system variables and marking the original ones as deprecated. This commit also resolves some legacy problems related to SET STATEMENT and transaction_isolation.
The transaction isolation levels READ COMMITTED and READ UNCOMMITTED
should behave similarly to the old deprecated setting
innodb_locks_unsafe_for_binlog=1, that is, avoid acquiring gap locks.
row_search_mvcc(): Reduce the scope of some variables, and clean up
the initialization and use of the variable set_also_gap_locks.
timestamp: Thu 2011-12-01 15:12:10 +0100
Fix for Bug#13430436 PERFORMANCE DEGRADATION IN SYSBENCH ON INNODB DUE TO ICP
When running sysbench on InnoDB there is a performance degradation due
to index condition pushdown (ICP). Several of the queries in sysbench
have a WHERE condition that the optimizer uses for executing these
queries as range scans. The upper and lower limit of the range scan
will ensure that the WHERE condition is fulfilled. Still, the WHERE
condition is part of the queries' condition and if ICP is enabled the
condition will be pushed down to InnoDB as an index condition.
Due to the range scan's upper and lower limits ensure that the WHERE
condition is fulfilled, the pushed index condition will not filter out
any records. As a result the use of ICP for these queries results in a
performance overhead for sysbench. This overhead comes from using
resources for determining the part of the condition that can be pushed
down to InnoDB and overhead in InnoDB for executing the pushed index
condition.
With the default configuration for sysbench the range scans will use
the primary key. This is a clustered index in InnoDB. Using ICP on a
clustered index provides the lowest performance benefit since the
entire record is part of the clustered index and in InnoDB it has the
highest relative overhead for executing the pushed index condition.
The fix for removing the overhead ICP introduces when running sysbench
is to disable use of ICP when the index used by the query is a
clustered index.
When WL#6061 is implemented this change should be re-evaluated.
Resolved all conflicts, bad merges and fixed a few minor bugs in the code.
Commented out the queries from multi_update, view, subselect_sj, func_str,
derived_view, view_grant that failed either with crashes in ps-protocol or
with wrong results.
The failures are clear indications of some bugs in the code and these bugs
are to be fixed.
