Release notes: Detached scheduler threads (#433)

* add detached scheduler threads to 3.10.13

* Apply suggestions from code review [skip ci]

---------

Co-authored-by: Simran <[email protected]>

Author: nerpaula

site/content/3.10/release-notes/version-3.10/whats-new-in-3-10.md

@@ -1621,6 +1621,27 @@ committed when a user requests a Hot Backup. The waiting could cause deadlocks
 and thus Hot Backups to fail, in particular in ArangoGraph. Now, Hot Backups are
 created immediately and commits have to wait until the backup process is done.
 
+### Detached scheduler threads
+
+<small>Introduced in: v3.10.13</small>
+
+A scheduler thread now has the capability to detach itself from the scheduler
+if it observes the need to perform a potentially long running task, like waiting
+for a lock. This allows a new scheduler thread to be started and prevents
+scenarios where all threads are blocked waiting for a lock, which has previously
+led to deadlock situations.
+
+Threads waiting for more than 1 second on a collection lock will detach
+themselves.
+
+The following startup option has been added:
+- `--server.max-number-detached-threads`: The maximum number of detached scheduler
+  threads.
+
+The following metric has been added:
+- `arangodb_scheduler_num_detached_threads`: The number of worker threads
+  currently started and detached from the scheduler.
+
 ## Client tools
 
 ### arangobench

site/content/3.11/release-notes/version-3.10/whats-new-in-3-10.md

@@ -1621,6 +1621,27 @@ committed when a user requests a Hot Backup. The waiting could cause deadlocks
 and thus Hot Backups to fail, in particular in ArangoGraph. Now, Hot Backups are
 created immediately and commits have to wait until the backup process is done.
 
+### Detached scheduler threads
+
+<small>Introduced in: v3.10.13</small>
+
+A scheduler thread now has the capability to detach itself from the scheduler
+if it observes the need to perform a potentially long running task, like waiting
+for a lock. This allows a new scheduler thread to be started and prevents
+scenarios where all threads are blocked waiting for a lock, which has previously
+led to deadlock situations.
+
+Threads waiting for more than 1 second on a collection lock will detach
+themselves.
+
+The following startup option has been added:
+- `--server.max-number-detached-threads`: The maximum number of detached scheduler
+  threads.
+
+The following metric has been added:
+- `arangodb_scheduler_num_detached_threads`: The number of worker threads
+  currently started and detached from the scheduler.
+
 ## Client tools
 
 ### arangobench

site/content/3.11/release-notes/version-3.11/whats-new-in-3-11.md

@@ -1291,7 +1291,7 @@ cache subsystem:
 
 ### Detached scheduler threads
 
-<small>Introduced in: v3.11.5</small>
+<small>Introduced in: v3.10.13, v3.11.5</small>
 
 A scheduler thread now has the capability to detach itself from the scheduler
 if it observes the need to perform a potentially long running task, like waiting

site/content/3.12/release-notes/version-3.10/whats-new-in-3-10.md

@@ -1621,6 +1621,27 @@ committed when a user requests a Hot Backup. The waiting could cause deadlocks
 and thus Hot Backups to fail, in particular in ArangoGraph. Now, Hot Backups are
 created immediately and commits have to wait until the backup process is done.
 
+### Detached scheduler threads
+
+<small>Introduced in: v3.10.13</small>
+
+A scheduler thread now has the capability to detach itself from the scheduler
+if it observes the need to perform a potentially long running task, like waiting
+for a lock. This allows a new scheduler thread to be started and prevents
+scenarios where all threads are blocked waiting for a lock, which has previously
+led to deadlock situations.
+
+Threads waiting for more than 1 second on a collection lock will detach
+themselves.
+
+The following startup option has been added:
+- `--server.max-number-detached-threads`: The maximum number of detached scheduler
+  threads.
+
+The following metric has been added:
+- `arangodb_scheduler_num_detached_threads`: The number of worker threads
+  currently started and detached from the scheduler.
+
 ## Client tools
 
 ### arangobench

site/content/3.12/release-notes/version-3.11/whats-new-in-3-11.md

@@ -1291,7 +1291,7 @@ cache subsystem:
 
 ### Detached scheduler threads
 
-<small>Introduced in: v3.11.5</small>
+<small>Introduced in: v3.10.13, v3.11.5</small>
 
 A scheduler thread now has the capability to detach itself from the scheduler
 if it observes the need to perform a potentially long running task, like waiting

site/content/3.12/release-notes/version-3.12/whats-new-in-3-12.md

@@ -577,7 +577,7 @@ cache subsystem:
 
 ### Detached scheduler threads
 
-<small>Introduced in: v3.11.5</small>
+<small>Introduced in: v3.10.13, v3.11.5</small>
 
 A scheduler thread now has the capability to detach itself from the scheduler
 if it observes the need to perform a potentially long running task, like waiting