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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
.github Fix remaining typos 2025-04-29 11:18:00 +10:00
BUILD Fix remaining typos 2025-04-29 11:18:00 +10:00
client Improvements to mtr 2025-04-28 12:59:39 +03:00
cmake Fix remaining typos 2025-04-29 11:18:00 +10:00
dbug Reënable ATTRIBUTE_FORMAT on DBUG_PRINT & t/eprint 2025-02-12 10:17:44 +01:00
debian Fix remaining typos 2025-04-29 11:18:00 +10:00
Docs Fix remaining typos 2025-04-29 11:18:00 +10:00
extra Fix remaining typos 2025-04-29 11:18:00 +10:00
include MDEV-36425 Extend read_only to also block share locks and super user 2025-04-28 12:59:39 +03:00
libmariadb@ba712ddf96 update C/C 2025-04-02 10:52:31 +11:00
libmysqld Fix remaining typos 2025-04-29 11:18:00 +10:00
libservices Merge 10.6 into 10.11 2024-02-08 15:04:46 +02:00
man Fix remaining typos 2025-04-29 11:18:00 +10:00
mysql-test MDEV-19749 - MDL scalability regression after backup locks 2025-06-06 10:57:29 +04:00
mysys Fix remaining typos 2025-04-29 11:18:00 +10:00
mysys_ssl MDEV-34712 Add support to sha2 and pbkdf2 key derivation in file_key_management 2025-04-28 13:43:32 +10:00
plugin MDL_lock encapsulation: MDL_lock::get_key() 2025-06-05 17:08:27 +04:00
randgen/conf Group commit for maria engine. 2010-02-12 15:12:28 +02:00
scripts Fix remaining typos 2025-04-29 11:18:00 +10:00
sql MDEV-19749 - MDL scalability regression after backup locks 2025-06-06 10:57:29 +04:00
sql-bench Fix remaining typos 2025-04-29 11:18:00 +10:00
sql-common MDEV-31334: Consider dates ending in 'T' as malformed 2025-04-15 14:39:42 +03:00
storage Fix typos in mysql-test/ 2025-04-29 13:53:16 +10:00
strings Fix remaining typos 2025-04-29 11:18:00 +10:00
support-files Fix remaining typos 2025-04-29 11:18:00 +10:00
tests Fix remaining typos 2025-04-29 11:18:00 +10:00
tpool Fix typos in C comments in miscellaneous files 2025-03-24 13:36:28 +11:00
unittest Fix typos in C comments in miscellaneous files 2025-03-24 13:36:28 +11:00
vio Fix remaining typos 2025-04-29 11:18:00 +10:00
win Fix remaining typos 2025-04-29 11:18:00 +10:00
wsrep-lib@70cd967f5e galera: wsrep-lib submodule update 2024-12-17 09:53:19 +01:00
zlib Merge branch 'merge-zlib' (1.3.1) into 10.4 2024-04-26 13:50:03 +02:00
.clang-format Remove duplicate key "Language" from .clang-format 2024-04-17 16:52:37 +02:00
.gitattributes Merge branch '10.5' into 10.6 2022-02-03 17:01:31 +01:00
.gitignore MDEV-34979 generate SBOM from server builds 2025-01-15 14:37:43 +01:00
.gitlab-ci.yml Fix remaining typos 2025-04-29 11:18:00 +10:00
.gitmodules Merge remote-tracking branch '10.4' into 10.5 2023-03-31 21:32:41 +02:00
appveyor.yml appveyor - run builds in "main" branch 2025-01-24 13:15:05 +01:00
BUILD-CMAKE Fix remaining typos 2025-04-29 11:18:00 +10:00
CMakeLists.txt Merge 11.4 into 11.8 2025-04-02 14:07:01 +03:00
CODING_STANDARDS.md Fix remaining typos 2025-04-29 11:18:00 +10:00
config.h.cmake Merge 11.4 into 11.8 2025-04-02 14:07:01 +03:00
configure.cmake Merge branch '11.6' into 11.7 2024-11-10 19:22:21 +01:00
CONTRIBUTING.md Add CODING_STANDARDS.md file 2023-02-03 15:47:17 +11:00
COPYING Update FSF Address 2019-05-11 21:29:06 +03:00
CREDITS Update sponsors 2024-08-12 09:32:30 +01:00
INSTALL-SOURCE Update AskMonty and Atlassian references to MariaDB 2016-03-08 15:24:01 +02:00
INSTALL-WIN-SOURCE Update AskMonty and Atlassian references to MariaDB 2016-03-08 15:24:01 +02:00
KNOWN_BUGS.txt Changed some MySQL names in messages to MariaDB 2018-12-09 20:49:05 +02:00
README.md Merge branch '10.11' into 11.1 2024-05-31 10:54:31 +10:00
SECURITY.md Create SECURITY.md 2023-06-05 08:28:06 +10:00
THIRDPARTY Update THIRDPARTY license file to reflect reality 2025-04-18 23:16:46 +02:00
VERSION bump the version 2025-04-18 17:11:09 +02:00

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MariaDB: The innovative open source database

MariaDB was designed as a drop-in replacement of MySQL(R) with more features, new storage engines, fewer bugs, and better performance.

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https://mariadb.com/kb/en/new-and-old-releases/

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