[RFC PATCH 2/5] maintenance: add fixed random delay to systemd timers

From: Max Gautier <mg@max.gautier.name>
To: git@vger.kernel.org
Cc: "Lénaïc Huard" <lenaic@lhuard.fr>, "Max Gautier" <mg@max.gautier.name>
Subject: [RFC PATCH 2/5] maintenance: add fixed random delay to systemd timers
Date: Mon, 18 Mar 2024 16:07:20 +0100	[thread overview]
Message-ID: <20240318151701.26644-4-mg@max.gautier.name> (raw)
In-Reply-To: <20240318151701.26644-2-mg@max.gautier.name>

Ensures that:
- git maintenance timers have a fixed time interval between execution.
- the three timers are not executed at the same time.

This is intended to implement an alternative to the two followings
commits:
c97ec0378b (maintenance: fix systemd schedule overlaps, 2023-08-10)
daa787010c (maintenance: use random minute in systemd scheduler, 2023-08-10)

Instead of manually adding a specific minute (which is reset on each
invocation of `git maintenance start`), we use systemd timers
RandomizedDelaySec and FixedRandomDelay functionalities.

From man systemd.timer:
>FixedRandomDelay=
>  Takes a boolean argument. When enabled, the randomized offset
>  specified by RandomizedDelaySec= is reused for all firings of the
>  same timer. For a given timer unit, **the offset depends on the
>  machine ID, user identifier and timer name**, which means that it is
>  stable between restarts of the manager. This effectively creates a
>  fixed offset for an individual timer, reducing the jitter in
>  firings of this timer, while still avoiding firing at the same time
>  as other similarly configured timers.

-> which is exactly the use case for git-maintenance timers.

Signed-off-by: Max Gautier <mg@max.gautier.name>
---
 systemd/user/git-maintenance@.service | 1 +
 systemd/user/git-maintenance@.timer   | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/systemd/user/git-maintenance@.service b/systemd/user/git-maintenance@.service
index 87ac0c86e6..f949e1a217 100644
--- a/systemd/user/git-maintenance@.service
+++ b/systemd/user/git-maintenance@.service
@@ -1,5 +1,6 @@
 [Unit]
 Description=Optimize Git repositories data
+Documentation=man:git-maintenance(1)
 
 [Service]
 Type=oneshot
diff --git a/systemd/user/git-maintenance@.timer b/systemd/user/git-maintenance@.timer
index 40fbc77a62..667c5998ba 100644
--- a/systemd/user/git-maintenance@.timer
+++ b/systemd/user/git-maintenance@.timer
@@ -1,9 +1,12 @@
 [Unit]
 Description=Optimize Git repositories data
+Documentation=man:git-maintenance(1)
 
 [Timer]
 OnCalendar=%i
 Persistent=true
+RandomizedDelaySec=1800
+FixedRandomDelay=true
 
 [Install]
 WantedBy=timers.target
-- 
2.44.0

