If the project is in a group, the `group.refresh_members_authorized_projects`
is made non-blocking, and we call `current_user.refresh_authorized_projects`
directly.
Projects in a personal namespace are more difficult. Rather than passing the
`blocking:` parameter through the entire `add_master` chain, have the
`AuthorizedProjectsWorker` automatically inline authorizations for three IDs or
less. Since the maximum number of IDs in this path is 2, that has the same effect.
There were two cases that could be problematic:
1. Because sometimes AuthorizedProjectsWorker would be scheduled in a
transaction it was possible for a job to run/complete before a
COMMIT; resulting in it either producing an error, or producing no
new data.
2. When scheduling jobs the code would not wait until completion. This
could lead to a user creating a project and then immediately trying
to push to it. Usually this will work fine, but given enough load it
might take a few seconds before a user has access.
The first one is problematic, the second one is mostly just annoying
(but annoying enough to warrant a solution).
This commit changes two things to deal with this:
1. Sidekiq scheduling now takes places after a COMMIT, this is ensured
by scheduling using Rails' after_commit hook instead of doing so in
an arbitrary method.
2. When scheduling jobs the calling thread now waits for all jobs to
complete.
Solution 2 requires tracking of job completions. Sidekiq provides a way
to find a job by its ID, but this involves scanning over the entire
queue; something that is very in-efficient for large queues. As such a
more efficient solution is necessary. There are two main Gems that can
do this in a more efficient manner:
* sidekiq-status
* sidekiq_status
No, this is not a joke. Both Gems do a similar thing (but slightly
different), and the only difference in their name is a dash vs an
underscore. Both Gems however provide far more than just checking if a
job has been completed, and both have their problems. sidekiq-status
does not appear to be actively maintained, with the last release being
in 2015. It also has some issues during testing as API calls are not
stubbed in any way. sidekiq_status on the other hand does not appear to
be very popular, and introduces a similar amount of code.
Because of this I opted to write a simple home grown solution. After
all, all we need is storing a job ID somewhere so we can efficiently
look it up; we don't need extra web UIs (as provided by sidekiq-status)
or complex APIs to update progress, etc.
This is where Gitlab::SidekiqStatus comes in handy. This namespace
contains some code used for tracking, removing, and looking up job IDs;
all without having to scan over an entire queue. Data is removed
explicitly, but also expires automatically just in case.
Using this API we can now schedule jobs in a fork-join like manner: we
schedule the jobs in Sidekiq, process them in parallel, then wait for
completion. By using Sidekiq we can leverage all the benefits such as
being able to scale across multiple cores and hosts, retrying failed
jobs, etc.
The one downside is that we need to make sure we can deal with
unexpected increases in job processing timings. To deal with this the
class Gitlab::JobWaiter (used for waiting for jobs to complete) will
only wait a number of seconds (30 by default). Once this timeout is
reached it will simply return.
For GitLab.com almost all AuthorizedProjectWorker jobs complete in
seconds, only very rarely do we spike to job timings of around a minute.
These in turn seem to be the result of external factors (e.g. deploys),
in which case a user is most likely not able to use the system anyway.
In short, this new solution should ensure that jobs are processed
properly and that in almost all cases a user has access to their
resources whenever they need to have access.
Prior to this commit the refreshing of authorized projects was done in
two steps:
1. Remove existing authorizations
2. Insert a new list of all authorizations
This can lead to a high amount of dead tuples as every time all rows are
being replaced. For example, if a user with 100 authorizations is given
access to a new project this would lead to:
* 100 rows being removed
* 101 new rows being inserted
This commit changes the way this system works so it only removes/inserts
what is necessary. Using the above example this would lead to only 1 new
row being inserted, with the initial 100 being left untouched.
Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/25257
When I proposed using serializable transactions I was hoping we would be
able to refresh data of individual users concurrently. Unfortunately
upon closer inspection it was revealed this was not the case. This could
result in a lot of queries failing due to serialization errors,
overloading the database in the process (given enough workers trying to
update the target table).
To work around this we're now using a Redis lease that is cancelled upon
completion. This ensures we can update the data of different users
concurrently without overloading the database.
The code will try to obtain the lease until it succeeds, waiting at
least 1 second between retries. This is necessary as we may otherwise
end up _not_ updating the data which is not an option.
