This is caused by a change of MySQL 5.7.3-m13. Please see the following URL for details.

"mysql - Creating tables and problems with primary key in Rails - Stack Overflow":http://stackoverflow.com/questions/21075515/creating-tables-and-problems-with-primary-key-in-rails

The "workaround":https://github.com/rails/rails/commit/26cea8fabe828e7b0535275044cb8316fff1c590 is included in Rails 4.1. But current Redmine is based on Rails 3.2, so it seems that we have to rely on "monkey patch":https://github.com/rails/rails/pull/13247#issuecomment-32425844 for now.

--------------------------------------------------------------------------------
Don't know what to do with this one, guess the patch can't be avoided?
--------------------------------------------------------------------------------
Probably this issue will be resolved in Redmine 3.0.0 because it is based on Rails 4.1.

--------------------------------------------------------------------------------
Same problem here using @redmine-2.6.0@.

<pre>
# mysqld --version
mysqld Ver 5.7.5-m15 for linux-glibc2.5 on x86_64 (MySQL Community Server (GPL))
# bundle exec rails --version
Rails 3.2.19
# ruby --version
ruby 2.1.2p95 (2014-05-08 revision 45877) [x86_64-linux-gnu]
</pre>
--------------------------------------------------------------------------------
If your're gonna wait for Rails 4 in Redmine 3, maybe an update to the docs to inform it's not compatible with this specific version of MySQL.
--------------------------------------------------------------------------------
Note about this incompatibillity added to [[RedmineInstall]].
--------------------------------------------------------------------------------
There are still some issues with mysql 5.7 and Rails 4.2:

# it does not pass the issue concurrency test (dead locks), although the "5.7 changelog":http://dev.mysql.com/doc/refman/5.7/en/mysql-nutshell.html does not mention any changes to the lock mechanism
# timestamps rouding issues after reload that trigger failures in @AccountTest#test_user_with_must_change_passwd_should_be_able_to_change_its_password@. Here is an example that shows a timestamp returning a different value after reload:

<pre>
irb(main):044:0> u=User.first
irb(main):045:0> u.created_on = "2015-02-15 09:38:59.767393"
=> "2015-02-15 09:38:59.767393"
irb(main):046:0> u.save
=> true
irb(main):047:0> u.created_on
=> Sun, 15 Feb 2015 09:38:59 UTC +00:00
irb(main):048:0> u.reload
irb(main):049:0> u.created_on
=> Sun, 15 Feb 2015 09:39:00 UTC +00:00
</pre>

A workaround was committed in r14011 for 2.
--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
Jean-Philippe Lang wrote:
> # it does not pass the issue concurrency test (dead locks), although the "5.7 changelog":http://dev.mysql.com/doc/refman/5.7/en/mysql-nutshell.html does not mention

http://dev.mysql.com/doc/refman/5.6/en/mysql-nutshell.html
> InnoDB uses a new, faster algorithm to detect deadlocks.
--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
Jean-Philippe Lang wrote:
> # it does not pass the issue concurrency test (dead locks)

#19344 says MySQL 5.6 too.

--------------------------------------------------------------------------------
Toshi MARUYAMA wrote:
> #19344 says MySQL 5.6 too.

Indeed, the CI server runs MySQL 5.1.

I had a deeper look at the deadlocks issue and it seems to work when doing @SELECT * ... FROM UPDATE@ instead of @SELECT id ... FOR UPDATE@. Here is a patch for current trunk tested with mysql5.7, the concurrency test passes for me. Could you give it a try?
--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
On my CentOS7 mariadb-5.5.41-2.el7_0.x86_64:

clean r14128:
<pre>
$ ruby test/unit/issue_nested_set_concurrency_test.rb
Run options: --seed 12276

# Running:

F.

Finished in 19.053029s, 0.1050 runs/s, 0.4199 assertions/s.

1) Failure:
IssueNestedSetConcurrencyTest#test_concurrency [test/unit/issue_nested_set_concurrency_test.rb:45]:
Expected "Mysql2::Error: Deadlock found when trying to get lock;
try restarting transaction:
SELECT `issues`.`id` FROM `issues` WHERE (root_id IN (SELECT root_id FROM issues WHERE id IN (319,316)))
ORDER BY `issues`.`id` ASC FOR UPDATE" to be nil.

2 runs, 8 assertions, 1 failures, 0 errors, 0 skips
</pre>

r14128 with note-13 patch:
<pre>
$ ruby test/unit/issue_nested_set_concurrency_test.rb
Run options: --seed 50424

# Running:

F.

Finished in 5.455071s, 0.3666 runs/s, 1.2832 assertions/s.

1) Failure:
IssueNestedSetConcurrencyTest#test_concurrency [test/unit/issue_nested_set_concurrency_test.rb:45]:
Expected "Mysql2::Error: Deadlock found when trying to get lock;
try restarting transaction:
SELECT `issues`.* FROM `issues` WHERE `issues`.`root_id` = 432
ORDER BY `issues`.`id` ASC FOR UPDATE" to be nil.

2 runs, 7 assertions, 1 failures, 0 errors, 0 skips

</pre>
--------------------------------------------------------------------------------
This change passes test half times, but fails half times on my MariaDB 5.5.
<pre><code class="diff">
diff --git a/lib/redmine/nested_set/issue_nested_set.rb b/lib/redmine/nested_set/issue_nested_set.rb
--- a/lib/redmine/nested_set/issue_nested_set.rb
+++ b/lib/redmine/nested_set/issue_nested_set.rb
@@ -158,7 +158,8 @@ module Redmine
self.class.reorder(:id).where(:root_id => sets_to_lock).lock(lock).ids
else
sets_to_lock = [id, parent_id].compact
- self.class.reorder(:id).where("root_id IN (SELECT root_id FROM #{self.class.table_name} WHERE id IN (?))", sets_to_lock).lock.ids
+ root_ids = self.class.where(:id => sets_to_lock).select(:root_id).to_a
+ self.class.where(:root_id => root_ids).lock.ids
end
end

</code></pre>

<pre>
$ ruby test/unit/issue_nested_set_concurrency_test.rb
Run options: --seed 63128

# Running:

..

Finished in 25.875842s, 0.0773 runs/s, 0.3865 assertions/s.

2 runs, 10 assertions, 0 failures, 0 errors, 0 skips

</pre>

<pre>
$ ruby test/unit/issue_nested_set_concurrency_test.rb
Run options: --seed 40861

# Running:

FF

Finished in 6.222392s, 0.3214 runs/s, 0.6428 assertions/s.

1) Failure:
IssueNestedSetConcurrencyTest#test_concurrency [test/unit/issue_nested_set_concurrency_test.rb:45]:
Expected "Mysql2::Error: Deadlock found when trying to get lock; try restarting transaction:
UPDATE `issues` SET lft = CASE WHEN lft > 9 THEN lft - 2 ELSE lft END, rgt = CASE WHEN rgt > 9 THEN rgt - 2 ELSE rgt END WHERE `issues`.`root_id` = 4249 AND (lft > 9 OR rgt > 9)" to be nil.

2) Failure:
IssueNestedSetConcurrencyTest#test_concurrent_subtasks_creation [test/unit/issue_nested_set_concurrency_test.rb:61]:
Expected "Mysql2::Error: Deadlock found when trying to get lock; try restarting transaction:
UPDATE `issues` SET lft = CASE WHEN lft >= 18 THEN lft + 2 ELSE lft END, rgt = CASE WHEN rgt >= 18 THEN rgt + 2 ELSE rgt END WHERE `issues`.`root_id` = 4263 AND (lft >= 18 OR rgt >= 18)" to be nil.

2 runs, 4 assertions, 2 failures, 0 errors, 0 skips

</pre>
--------------------------------------------------------------------------------
Toshi, your patch does not do what it's supposed to.

You may want to write:

root_ids = self.class.where(:id => sets_to_lock).pluck(:root_id)

instead of:

root_ids = self.class.where(:id => sets_to_lock).select(:root_id).to_a

which returns records without their ids. The lock after that does nothing:

SELECT `issues`.`id` FROM `issues` WHERE `issues`.`root_id` IS NULL FOR UPDATE
--------------------------------------------------------------------------------
I've isolated the log for a thread that triggers a dead lock. It ends with:

<pre>
[52206168] BEGIN
[52206168] SELECT `issues`.* FROM `issues` WHERE `issues`.`id` = 781 LIMIT 1
[52206168] SELECT `issues`.`id` FROM `issues` WHERE `issues`.`root_id` = 778 ORDER BY `issues`.`id` ASC FOR UPDATE
[52206168] ROLLBACK
[52206168] ERROR: Mysql2::Error: Deadlock found when trying to get lock; try restarting transaction:
SELECT `issues`.`id` FROM `issues` WHERE `issues`.`root_id` = 778 ORDER BY `issues`.`id` ASC FOR UPDATE
</pre>

As we can see, the thread starts a transaction, has no lock yet and gets a dead lock error on the first lock. Anyone knows what would explain that?
--------------------------------------------------------------------------------
Jean-Philippe Lang wrote:
> Toshi, your patch does not do what it's supposed to.
>
> You may want to write:
>
> root_ids = self.class.where(:id => sets_to_lock).pluck(:root_id)
>
> instead of:
>
> root_ids = self.class.where(:id => sets_to_lock).select(:root_id).to_a
>
> which returns records without their ids. The lock after that does nothing:
>
> SELECT `issues`.`id` FROM `issues` WHERE `issues`.`root_id` IS NULL FOR UPDATE

This changes fails 3/4 times.

<pre><code class="diff">
diff --git a/lib/redmine/nested_set/issue_nested_set.rb b/lib/redmine/nested_set/issue_nested_set.rb
--- a/lib/redmine/nested_set/issue_nested_set.rb
+++ b/lib/redmine/nested_set/issue_nested_set.rb
@@ -158,7 +158,8 @@ module Redmine
self.class.reorder(:id).where(:root_id => sets_to_lock).lock(lock).ids
else
sets_to_lock = [id, parent_id].compact
- self.class.reorder(:id).where("root_id IN (SELECT root_id FROM #{self.class.table_name} WHERE id IN (?))", sets_to_lock).lock.ids
+ root_ids = self.class.where(:id => sets_to_lock).pluck(:root_id).compact.uniq
+ self.class.where(:root_id => root_ids).lock.ids
end
end
</code></pre>

<pre>
$ ruby test/unit/issue_nested_set_concurrency_test.rb
Run options: --seed 1553

# Running:

F.

Finished in 20.314407s, 0.0985 runs/s, 0.4430 assertions/s.

1) Failure:
IssueNestedSetConcurrencyTest#test_concurrency [test/unit/issue_nested_set_concurrency_test.rb:45]:
Expected "Mysql2::Error: Deadlock found when trying to get lock; try restarting transaction: SELECT `issues`.`id` FROM `issues` WHERE `issues`.`root_id` = 7049 FOR UPDATE" to be nil.

2 runs, 9 assertions, 1 failures, 0 errors, 0 skips

</pre>
--------------------------------------------------------------------------------
"SET SESSION TRANSACTION ISOLATION LEVEL SERIALIZABLE;" reduces failure times on my MariaDB 5.5.

--------------------------------------------------------------------------------
This is code from source:tags/2.6.3/lib/plugins/awesome_nested_set/lib/awesome_nested_set/model/transactable.rb .

<pre><code class="diff">
diff --git a/lib/redmine/nested_set/issue_nested_set.rb b/lib/redmine/nested_set/issue_nested_set.rb
--- a/lib/redmine/nested_set/issue_nested_set.rb
+++ b/lib/redmine/nested_set/issue_nested_set.rb
@@ -148,7 +148,29 @@ module Redmine
new_record? || !is_or_is_ancestor_of?(issue)
end

+ def in_tenacious_transaction(&block)
+ retry_count = 0
+ begin
+ transaction(&block)
+ rescue ActiveRecord::StatementInvalid => error
+ raise unless error.message =~ /Deadlock found when trying to get lock/
+ raise unless retry_count < 10
+ retry_count += 1
+ logger.info "Deadlock detected on retry #{retry_count}, restarting transaction"
+ sleep(rand(retry_count)*0.1) # Aloha protocol
+ retry
+ end
+ end
+
def lock_nested_set
+ if self.class.connection.adapter_name =~ /mysql/i
+ in_tenacious_transaction { lock_nested_set_in_tenacious_transaction }
+ else
+ lock_nested_set_in_tenacious_transaction
+ end
+ end
+
+ def lock_nested_set_in_tenacious_transaction
if self.class.connection.adapter_name =~ /sqlserver/i
lock = "WITH (ROWLOCK HOLDLOCK UPDLOCK)"
# Custom lock for SQLServer

</code></pre>
--------------------------------------------------------------------------------
Note-20 is wrong because it uses nested transaction and parent transaction does not use lock.
This is fix.

<pre><code class="diff">
diff --git a/lib/redmine/nested_set/issue_nested_set.rb b/lib/redmine/nested_set/issue_nested_set.rb
--- a/lib/redmine/nested_set/issue_nested_set.rb
+++ b/lib/redmine/nested_set/issue_nested_set.rb
@@ -148,7 +148,29 @@ module Redmine
new_record? || !is_or_is_ancestor_of?(issue)
end

+ def get_lock_mysql(&block)
+ retry_count = 0
+ begin
+ yield
+ rescue ActiveRecord::StatementInvalid => error
+ raise unless error.message =~ /Deadlock found when trying to get lock/
+ raise unless retry_count < 10
+ retry_count += 1
+ logger.info "Deadlock detected on retry #{retry_count}, restarting transaction"
+ sleep(rand(retry_count)*0.1) # Aloha protocol
+ retry
+ end
+ end
+
def lock_nested_set
+ if self.class.connection.adapter_name =~ /mysql/i
+ get_lock_mysql { get_lock }
+ else
+ get_lock
+ end
+ end
+
+ def get_lock
if self.class.connection.adapter_name =~ /sqlserver/i
lock = "WITH (ROWLOCK HOLDLOCK UPDLOCK)"
# Custom lock for SQLServer
</code></pre>
--------------------------------------------------------------------------------
Toshi, the idea of the implementation of nested sets in 3.0.0 is to start the transaction by locking all the rows that might be updated or used to compute shifts in the transaction, in order by prevent dead locks and inconsistencies. I won't commit that workaround until I figure out why it doesn't work as I expect (note-17) in recent versions of MySQL.
--------------------------------------------------------------------------------
I think MySQL uses *Gap Locks*, so we cannot avoid deadlock.
http://dev.mysql.com/doc/refman/5.6/en/innodb-record-level-locks.html#idm140169015854080

I tried *READ COMMITTED* on MariaDB 5.5, but deadlock raised. I don't know the reason.
--------------------------------------------------------------------------------
Do current versions of Redmine still not support MySQL 5.7?
--------------------------------------------------------------------------------
#23318#note-18 patch reduces test failure times from about 100% to 50% on my CentOS7 mariadb-5.5.52-1.el7.x86_64.
--------------------------------------------------------------------------------
Latest versions of Ubuntu server only provide the 5.7 package, version 5.5 is really difficult to install on it: https://askubuntu.com/questions/763240/is-it-possible-to-install-mysql-5-5-or-5-6-on-ubuntu-16-04
--------------------------------------------------------------------------------
Here are some logs from MySQL 5.7:

<pre>
mysql> select * FROM INNODB_LOCKS \G;
*************************** 1. row ***************************
lock_id: 56163:265:12:54
lock_trx_id: 56163
lock_mode: X
lock_type: RECORD
lock_table: `redmine_test`.`issues`
lock_index: index_issues_on_root_id_and_lft_and_rgt
lock_space: 265
lock_page: 12
lock_rec: 54
lock_data: 653, 1, 20, 653
*************************** 2. row ***************************
lock_id: 56159:265:12:54
lock_trx_id: 56159
lock_mode: X
lock_type: RECORD
lock_table: `redmine_test`.`issues`
lock_index: index_issues_on_root_id_and_lft_and_rgt
lock_space: 265
lock_page: 12
lock_rec: 54
lock_data: 653, 1, 20, 653
2 rows in set, 1 warning (0.00 sec)

mysql> SHOW ENGINE INNODB STATUS \G;
------------------------
LATEST DETECTED DEADLOCK
------------------------
2017-04-23 14:38:12 0x7f308c273700

*** (1) TRANSACTION:
TRANSACTION 56161, ACTIVE 0 sec starting index read
mysql tables in use 2, locked 1
LOCK WAIT 2 lock struct(s), heap size 1136, 1 row lock(s)
MySQL thread id 9, OS thread handle 139846486136576, query id 1081 localhost root Sending data
SELECT `issues`.`id` FROM `issues` WHERE (root_id IN (SELECT root_id FROM issues WHERE id IN (658,655))) ORDER BY `issues`.`id` ASC FOR UPDATE

*** (1) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 265 page no 12 n bits 160 index index_issues_on_root_id_and_lft_and_rgt of table `redmine_test`.`issues` trx id 56161 lock_mode X waiting

Record lock, heap no 47 PHYSICAL RECORD: n_fields 4; compact format; info bits 32
0: len 4; hex 8000028d; asc ;;
1: len 4; hex 80000001; asc ;;
2: len 4; hex 80000016; asc ;;
3: len 4; hex 8000028d; asc ;;

*** (2) TRANSACTION:
TRANSACTION 56159, ACTIVE 0 sec updating or deleting
mysql tables in use 1, locked 1
5 lock struct(s), heap size 1136, 60 row lock(s), undo log entries 1
MySQL thread id 7, OS thread handle 139846486537984, query id 1134 localhost root updating
UPDATE `issues` SET lft = CASE WHEN lft > 5 THEN lft - 2 ELSE lft END, rgt = CASE WHEN rgt > 5 THEN rgt - 2 ELSE rgt END WHERE `issues`.`root_id` = 653 AND (lft > 5 OR rgt > 5)
*** (2) HOLDS THE LOCK(S):
RECORD LOCKS space id 265 page no 12 n bits 160 index index_issues_on_root_id_and_lft_and_rgt of table `redmine_test`.`issues` trx id 56159 lock_mode X

Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0
0: len 8; hex 73757072656d756d; asc supremum;;

Record lock, heap no 47 PHYSICAL RECORD: n_fields 4; compact format; info bits 32
0: len 4; hex 8000028d; asc ;;
1: len 4; hex 80000001; asc ;;
2: len 4; hex 80000016; asc ;;
3: len 4; hex 8000028d; asc ;;

*** (2) WAITING FOR THIS LOCK TO BE GRANTED:
RECORD LOCKS space id 265 page no 12 n bits 160 index index_issues_on_root_id_and_lft_and_rgt of table `redmine_test`.`issues` trx id 56159 lock_mode X locks gap before rec insert intention waiting

Record lock, heap no 47 PHYSICAL RECORD: n_fields 4; compact format; info bits 32
0: len 4; hex 8000028d; asc ;;
1: len 4; hex 80000001; asc ;;
2: len 4; hex 80000016; asc ;;
3: len 4; hex 8000028d; asc ;;

*** WE ROLL BACK TRANSACTION (1)

</pre>
--------------------------------------------------------------------------------
Should we put the index on :issues => [:root_id, :lft, :rgt] as unique? I think this would play a role in the number of records being locked when we do something such as:

<pre>
In remove_from_nested_set:
self.class.where(:root_id => root_id).where("lft >= ? AND rgt <= ?", lft, rgt).update_all(...)

In add_to_nested_set:
self.class.where(:root_id => root_id).where("lft >= ? OR rgt >= ?", lft, lft).update_all(...)
</pre>

Or is a reorder needed before the update_all clause ?
--------------------------------------------------------------------------------
Am about to make the move to Ubuntu 16.04. Can I install Redmine 3.3 and stick with MySQL 5.7 now?
--------------------------------------------------------------------------------
Mark Anderson wrote:
> Am about to make the move to Ubuntu 16.04. Can I install Redmine 3.3 and stick with MySQL 5.7 now?

For what it is worth, we have been using an Ubuntu 16.04 + MariaDB 10.0.x setup for over six months now without any obvious issues.

* web server: Ubuntu 16.04, nginx/Passenger, mysql-client 5.7.x
* database server: MariaDB 10.0.x
--------------------------------------------------------------------------------
@Stephane Evr - Hi, the index on :issues => [:root_id, :lft, :rgt] should be definitely unique.

To avoid duplicate entries during shifts I added an additional reorder statment:
<pre>
remove_from_nested_set
.reorder('lft desc')
add_to_nested_set
.reorder('lft asc')
</pre>

but it didn't help anyway, I think it's because shifts are overlapping, especially during creating & deleting records at the same time.

unfortunatelly awesome_nested_set has the same issue

locking all issues instead of subtree works correctly (no deadlocks), but it should be definitely avoided for performance reasons
self.class.reorder(:id).lock

log
<pre>
# Running:

Deadlock detected on getting lock, restarting transaction retry #1 thread: 107872360
Deadlock detected on update, restarting transaction retry #1 thread: 107872360
Deadlock detected on getting lock, restarting transaction retry #1 thread: 107863660
Deadlock detected on getting lock, restarting transaction retry #1 thread: 107872360
Deadlock detected on getting lock, restarting transaction retry #1 thread: 107863880
Deadlock detected on getting lock, restarting transaction retry #2 thread: 107863880
Deadlock detected on getting lock, restarting transaction retry #1 thread: 107872360
Deadlock detected on update, restarting transaction retry #1 thread: 107872360
Deadlock detected on getting lock, restarting transaction retry #1 thread: 107863880
Deadlock detected on getting lock, restarting transaction retry #1 thread: 107863880
Deadlock detected on update, restarting transaction retry #1 thread: 107863880
Deadlock detected on getting lock, restarting transaction retry #1 thread: 107863880
Deadlock detected on getting lock, restarting transaction retry #1 thread: 107863880
Deadlock detected on getting lock, restarting transaction retry #1 thread: 107863880
Deadlock detected on getting lock, restarting transaction retry #1 thread: 107863880
Deadlock detected on getting lock, restarting transaction retry #1 thread: 107863880
Deadlock detected on getting lock, restarting transaction retry #1 thread: 107863880
Deadlock detected on getting lock, restarting transaction retry #1 thread: 107863660
Deadlock detected on getting lock, restarting transaction retry #1 thread: 107872360
Deadlock detected on getting lock, restarting transaction retry #1 thread: 107863880
Deadlock detected on getting lock, restarting transaction retry #1 thread: 107863660
Deadlock detected on getting lock, restarting transaction retry #1 thread: 107872360
..

Finished in 14.603111s, 0.1370 runs/s, 0.6848 assertions/s.

2 runs, 10 assertions, 0 failures, 0 errors, 0 skips
</pre>
--------------------------------------------------------------------------------
Hi,
what is the highest tested version of MySql that is supported in Redmine 3.x - 4.x
thanks
--------------------------------------------------------------------------------
yossi edri wrote:
> Hi,
> what is the highest tested version of MySql that is supported in Redmine 3.x - 4.x
> thanks

Salam

redmine 3.2 work by last version of mysql but redmine 3.3 and higher not work well with mysql 5.5 or higher
--------------------------------------------------------------------------------
Just installed Redmine in following ports for FreeBSD. There are included mysql56, and the lowest version available from ports is mysql55. I've been trying Redmine with mysql80. Seems working for the case of mysql. But I got this issue - http://www.redmine.org/boards/2/topics/55693.
--------------------------------------------------------------------------------
Does it make sense to retry the transaction inside the @Issue@ class?

In @app/models/issue.rb@:

<pre><code class="ruby">
def self.transaction(options={}, &block)
retry_count = 0
begin
super
rescue ActiveRecord::StatementInvalid => error
raise if connection.adapter_name !~ /mysql/i
raise if error.message !~ /Deadlock found when trying to get lock/
raise if retry_count == 10
retry_count += 1
wait_ms = rand(retry_count * 100)
if logger
logger.info("Deadlock found when saving #{self}: "\
"Waiting for #{wait_ms} ms before restarting the transaction (retry ##{retry_count})")
end
sleep(wait_ms / 1000.0)
retry
end
end
</code></pre>

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
Even if the problem with deadlocks still exists on MySQL 5.7, I think that it is safe to say that Redmine 4.0 officially supports MySQL 5.7 and to close this issue.

CI server run the tests on MySQL 5.7 and the install documentation has been updated.

What do you think?
--------------------------------------------------------------------------------
> Even if the problem with deadlocks still exists on MySQL 5.7, I think that it is safe to say that Redmine 4.0 officially supports MySQL 5.7 and to close this issue.
>
> CI server run the tests on MySQL 5.7 and the install documentation has been updated.
>
> What do you think?

Loose tangent: Does the same also apply to MariaDB? FWIW, I've run Redmine on MariaDB 10.0 for years without (apparent) issue, hoping to upgrade to a newer MariaDB release in the near future.
--------------------------------------------------------------------------------
Deoren Moor wrote:
> > Even if the problem with deadlocks still exists on MySQL 5.7, I think that it is safe to say that Redmine 4.0 officially supports MySQL 5.7 and to close this issue.
> >
> > CI server run the tests on MySQL 5.7 and the install documentation has been updated.
> >
> > What do you think?
>
> Loose tangent: Does the same also apply to MariaDB? FWIW, I've run Redmine on MariaDB 10.0 for years without (apparent) issue, hoping to upgrade to a newer MariaDB release in the near future.

No, it applies only to MySQL 5.7. MariaDB is not supported (or at least officially) and an user reported some failing tests (please see #30367).
--------------------------------------------------------------------------------
Marius BALTEANU wrote:
> Even if the problem with deadlocks still exists on MySQL 5.7, I think that it is safe to say that Redmine 4.0 officially supports MySQL 5.7 and to close this issue.
>
> CI server run the tests on MySQL 5.7 and the install documentation has been updated.
>
> What do you think?

Tests skip on MySQL (r16926).

--------------------------------------------------------------------------------
Toshi MARUYAMA wrote:
> Marius BALTEANU wrote:
> > Even if the problem with deadlocks still exists on MySQL 5.7, I think that it is safe to say that Redmine 4.0 officially supports MySQL 5.7 and to close this issue.
> >
> > CI server run the tests on MySQL 5.7 and the install documentation has been updated.
> >
> > What do you think?
>
> Tests skip on MySQL (r16926).

Yes, but the CI uses MySQL 5.7 so is quite strange to say we do not support MySQL 5.7, but we run the tests against MySQL 5.7.

--------------------------------------------------------------------------------

relates,New,19344,MySQL 5.6: IssueNestedSetConcurrencyTest#test_concurrency : always fails
duplicates,Closed,28414,Does Redmine compatible with MySQL 5.7 or not ?