Remove outdated Redis cleanup doc

doc/administration/operations/cleaning_up_redis_sessions.md

 ---
-stage: Enablement
-group: Distribution
-info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
+redirect_to: 'index.md'
+remove_date: '2021-12-10'
 ---
 
-# Cleaning up stale Redis sessions **(FREE SELF)**
+This document was moved to [another location](index.md).
 
-Since version 6.2, GitLab stores web user sessions as key-value pairs in Redis.
-Prior to GitLab 7.3, user sessions did not automatically expire from Redis. If
-you have been running a large GitLab server (thousands of users) since before
-GitLab 7.3 we recommend cleaning up stale sessions to compact the Redis
-database after you upgrade to GitLab 7.3. You can also perform a cleanup while
-still running GitLab 7.2 or older, but in that case new stale sessions will
-start building up again after you clean up.
-
-In GitLab versions prior to 7.3.0, the session keys in Redis are 16-byte
-hexadecimal values such as '976aa289e2189b17d7ef525a6702ace9'. Starting with
-GitLab 7.3.0, the keys are
-prefixed with `session:gitlab:`, so they would look like
-`session:gitlab:976aa289e2189b17d7ef525a6702ace9`. Below we describe how to
-remove the keys in the old format.
-
-NOTE:
-The instructions below must be modified in accordance with your
-configuration settings if you have used the advanced Redis
-settings outlined in
-[Configuration Files Documentation](https://gitlab.com/gitlab-org/gitlab/-/blob/master/config/README.md).
-
-First we define a shell function with the proper Redis connection details.
-
-```shell
-rcli() {
-  # This example works for Omnibus installations of GitLab 7.3 or newer. For an
-  # installation from source you will have to change the socket path and the
-  # path to redis-cli.
-  sudo /opt/gitlab/embedded/bin/redis-cli -s /var/opt/gitlab/redis/redis.socket "$@"
-}
-
-# test the new shell function; the response should be PONG
-rcli ping
-```
-
-Now we do a search to see if there are any session keys in the old format for
-us to clean up.
-
-```shell
-# returns the number of old-format session keys in Redis
-rcli keys '*' | grep '^[a-f0-9]\{32\}$' | wc -l
-```
-
-If the number is larger than zero, you can proceed to expire the keys from
-Redis. If the number is zero there is nothing to clean up.
-
-```shell
-# Tell Redis to expire each matched key after 600 seconds.
-rcli keys '*' | grep '^[a-f0-9]\{32\}$' | awk '{ print "expire", $0, 600 }' | rcli
-# This will print '(integer) 1' for each key that gets expired.
-```
-
-Over the next 15 minutes (10 minutes expiry time plus 5 minutes Redis
-background save interval) your Redis database will be compacted. If you are
-still using GitLab 7.2, users who are not clicking around in GitLab during the
-10 minute expiry window will be signed out of GitLab.
+<!-- This redirect file can be deleted after 2021-12-10. -->
+<!-- Before deletion, see: https://docs.gitlab.com/ee/development/documentation/#move-or-rename-a-page -->

doc/administration/operations/index.md

@@ -8,11 +8,6 @@ info: To determine the technical writer assigned to the Stage/Group associated w
 
 Keep your GitLab instance up and running smoothly.
 
-- [Clean up Redis sessions](cleaning_up_redis_sessions.md): Prior to GitLab 7.3,
-  user sessions did not automatically expire from Redis. If
-  you have been running a large GitLab server (thousands of users) since before
-  GitLab 7.3 we recommend cleaning up stale sessions to compact the Redis
-  database after you upgrade to GitLab 7.3.
 - [Rake tasks](../../raketasks/index.md): Tasks for common administration and operational processes such as
   [cleaning up unneeded items from GitLab instance](../../raketasks/cleanup.md), integrity checks,
   and more.

doc/raketasks/cleanup.md

@@ -207,10 +207,6 @@ sudo gitlab-rake gitlab:cleanup:sessions:active_sessions_lookup_keys
 bundle exec rake gitlab:cleanup:sessions:active_sessions_lookup_keys RAILS_ENV=production
 ```
 
-## Cleaning up stale Redis sessions
-
-[Clean up stale sessions](../administration/operations/cleaning_up_redis_sessions.md) to compact the Redis database after you upgrade to GitLab 7.3.
-
 ## Container Registry garbage collection
 
 Container Registry can use considerable amounts of disk space. To clear up