mariadb/mysql-test
Sergey Vojtovich 23566b6924 MDEV-19749 - MDL scalability regression after backup locks
Statements that intend to modify data have to acquire protection
against ongoing backup. Prior to backup locks, protection against
FTWRL was acquired in form of 2 shared metadata locks of GLOBAL
(global read lock) and COMMIT namespaces. These two namespaces
were separate entities, they didn't share data structures and
locking primitives. And thus they were separate contention
points.

With backup locks, introduced by 7a9dfdd, these namespaces were
combined into a single BACKUP namespace. It became a single
contention point, which doubled load on BACKUP namespace data
structures and locking primitives compared to GLOBAL and COMMIT
namespaces. In other words system throughput has halved.

MDL fast lanes solve this problem by allowing multiple contention
points for single MDL_lock. Fast lane is scalable multi-instance
registry for leightweight locks. Internally it is just a list of
granted tickets, close counter and a mutex.

Number of fast lanes (or contention points) is defined by the
metadata_locks_instances system variable. Value of 1 disables fast
lanes and lock requests are served by conventional MDL_lock data
structures.

Since fast lanes allow arbitrary number of contention points, they
outperform pre-backup locks GLOBAL and COMMIT.

Fast lanes are enabled only for BACKUP namespace. Support for other
namespaces is to be implemented separately.

Lock types are divided in 2 categories: lightweight and heavyweight.

Lightweight lock types represent DML: MDL_BACKUP_DML,
MDL_BACKUP_TRANS_DML, MDL_BACKUP_SYS_DML, MDL_BACKUP_DDL,
MDL_BACKUP_ALTER_COPY, MDL_BACKUP_COMMIT. They are fully compatible
with each other. Normally served by corresponding fast lane, which is
determined by thread_id % metadata_locks_instances.

Heavyweight lock types represent ongoing backup: MDL_BACKUP_START,
MDL_BACKUP_FLUSH, MDL_BACKUP_WAIT_FLUSH, MDL_BACKUP_WAIT_DDL,
MDL_BACKUP_WAIT_COMMIT, MDL_BACKUP_FTWRL1, MDL_BACKUP_FTWRL2,
MDL_BACKUP_BLOCK_DDL. These locks are always served by conventional
MDL_lock data structures. Whenever such lock is requested, fast
lanes are closed and all tickets registered in fast lanes are
moved to conventional MDL_lock data structures. Until such locks
are released or aborted, lightweight lock requests are served by
conventional MDL_lock data structures.

Strictly speaking moving tickets from fast lanes to conventional
MDL_lock data structures is not required. But it allows to reduce
complexity and keep intact methods like: MDL_lock::visit_subgraph(),
MDL_lock::notify_conflicting_locks(), MDL_lock::reschedule_waiters(),
MDL_lock::can_grant_lock().

It is not even required to register tickets in fast lanes. They
can be implemented basing on an atomic variable that holds two
counters: granted lightweight locks and granted/waiting heavyweight
locks. Similarly to MySQL solution, which roughly speaking has
"single atomic fast lane". However it appears to be it won't bring
any better performance, while code complexity is going to be much
higher.
2025-06-06 10:57:29 +04:00
..
collections
include Fix typos in mysql-test/ 2025-04-29 13:53:16 +10:00
lib Fix typos in mysql-test/ 2025-04-29 13:53:16 +10:00
main MDEV-19749 - MDL scalability regression after backup locks 2025-06-06 10:57:29 +04:00
std_data Fix typos in mysql-test/ 2025-04-29 13:53:16 +10:00
suite MDEV-19749 - MDL scalability regression after backup locks 2025-06-06 10:57:29 +04:00
asan.supp
CMakeLists.txt Merge branch '10.5' into 10.6 2025-03-31 12:12:50 +02:00
dgcov.pl
lsan.supp
mariadb-stress-test.pl Fix typos in mysql-test/ 2025-04-29 13:53:16 +10:00
mariadb-test-run.pl Fix typos in mysql-test/ 2025-04-29 13:53:16 +10:00
mtr.out-of-source
purify.supp
README
README-gcov
README.stress
suite.pm
valgrind.supp Fix typos in mysql-test/ 2025-04-29 13:53:16 +10:00

This directory contains test suites for the MariaDB server. To run
currently existing test cases, execute ./mysql-test-run in this directory.

Some tests are known to fail on some platforms or be otherwise unreliable.
In the file collections/smoke_test there is a list of tests that are
expected to be stable.

In general you do not have to do "make install", and you can have
a co-existing MariaDB installation, the tests will not conflict with it.
To run the tests in a source directory, you must do "make" first.

In Red Hat distributions, you should run the script as user "mysql".
The user is created with nologin shell, so the best bet is something like
  # su -
  # cd /usr/share/mariadb-test
  # su -s /bin/bash mysql -c ./mysql-test-run

This will use the installed MariaDB executables, but will run a private
copy of the server process (using data files within /usr/share/mariadb-test),
so you need not start the mysqld service beforehand.

You can omit --skip-test-list option if you want to check whether
the listed failures occur for you.

To clean up afterwards, remove the created "var" subdirectory, e.g.
  # su -s /bin/bash - mysql -c "rm -rf /usr/share/mariadb-test/var"

If tests fail on your system, please read the following manual section
for instructions on how to report the problem:

https://mariadb.com/kb/en/reporting-bugs

If you want to use an already running MySQL server for specific tests,
use the --extern option to mysql-test-run. Please note that in this mode,
you are expected to provide names of the tests to run.

For example, here is the command to run the "alias" and "analyze" tests
with an external server:

  # mariadb-test-run --extern socket=/tmp/mysql.sock alias analyze

To match your setup, you might need to provide other relevant options.

With no test names on the command line, mysql-test-run will attempt
to execute the default set of tests, which will certainly fail, because
many tests cannot run with an external server (they need to control the
options with which the server is started, restart the server during
execution, etc.)

You can create your own test cases. To create a test case, create a new
file in the main subdirectory using a text editor. The file should have a .test
extension. For example:

  # xemacs t/test_case_name.test

In the file, put a set of SQL statements that create some tables,
load test data, and run some queries to manipulate it.

Your test should begin by dropping the tables you are going to create and
end by dropping them again. This ensures that you can run the test over
and over again.

If you are using mysqltest commands in your test case, you should create
the result file as follows:

  # mariadb-test-run --record test_case_name

  or

  # mariadb-test --record < t/test_case_name.test

If you only have a simple test case consisting of SQL statements and
comments, you can create the result file in one of the following ways:

  # mariadb-test-run --record test_case_name

  # mariadb test < t/test_case_name.test > r/test_case_name.result

  # mariadb-test --record --database test --result-file=r/test_case_name.result < t/test_case_name.test

When this is done, take a look at r/test_case_name.result.
If the result is incorrect, you have found a bug. In this case, you should
edit the test result to the correct results so that we can verify that
the bug is corrected in future releases.

If you want to submit your test case you can send it
to developers@lists.mariadb.org or attach it to a bug report on
http://mariadb.org/jira/.

If the test case is really big or if it contains 'not public' data,
then put your .test file and .result file(s) into a tar.gz archive,
add a README that explains the problem, ftp the archive to
ftp://ftp.mariadb.org/private and submit a report to
https://mariadb.org/jira about it.

The latest information about mysql-test-run can be found at:
https://mariadb.com/kb/en/mariadb/mysqltest/

If you want to create .rdiff files, check
https://mariadb.com/kb/en/mariadb/mysql-test-auxiliary-files/