This PR fixes a bug where projections could skip events if they were
written within the same microsecond, which can occur during high load on
different transactions.
## Problem
The event query ordering was not fully deterministic. Events created at
the exact same time (same `position`) and in the same transaction
(`in_tx_order`) were not guaranteed to be returned in the same order on
subsequent queries. This could lead to some events being skipped by the
projection logic.
## Solution
To solve this, the `ORDER BY` clause for event queries has been extended
to include `instance_id`, `aggregate_type`, and `aggregate_id`. This
ensures a stable and deterministic ordering for all events, even if they
share the same timestamp.
## Additionally changes:
* Replaced a manual slice search with the more idiomatic
`slices.Contains` to skip already projected instances.
* Changed the handling of already locked projections to log a debug
message and skip execution instead of returning an error.
* Ensures the database transaction is explicitly committed.
This PR overhauls our event projection system to make it more robust and
prevent skipped events under high load. The core change replaces our
custom, transaction-based locking with standard PostgreSQL advisory
locks. We also introduce a worker pool to manage concurrency and prevent
database connection exhaustion.
### Key Changes
* **Advisory Locks for Projections:** Replaces exclusive row locks and
inspection of `pg_stat_activity` with PostgreSQL advisory locks for
managing projection state. This is a more reliable and standard approach
to distributed locking.
* **Simplified Await Logic:** Removes the complex logic for awaiting
open transactions, simplifying it to a more straightforward time-based
filtering of events.
* **Projection Worker Pool:** Implements a worker pool to limit
concurrent projection triggers, preventing connection exhaustion and
improving stability under load. A new `MaxParallelTriggers`
configuration option is introduced.
### Problem Solved
Under high throughput, a race condition could cause projections to miss
events from the eventstore. This led to inconsistent data in projection
tables (e.g., a user grant might be missing). This PR fixes the
underlying locking and concurrency issues to ensure all events are
processed reliably.
### How it Works
1. **Event Writing:** When writing events, a *shared* advisory lock is
taken. This signals that a write is in progress.
2. **Event Handling (Projections):**
* A projection worker attempts to acquire an *exclusive* advisory lock
for that specific projection. If the lock is already held, it means
another worker is on the job, so the current one backs off.
* Once the lock is acquired, the worker briefly acquires and releases
the same *shared* lock used by event writers. This acts as a barrier,
ensuring it waits for any in-flight writes to complete.
* Finally, it processes all events that occurred before its transaction
began.
### Additional Information
* ZITADEL no longer modifies the `application_name` PostgreSQL variable
during event writes.
* The lock on the `current_states` table is now `FOR NO KEY UPDATE`.
* Fixes https://github.com/zitadel/zitadel/issues/8509
---------
Co-authored-by: Copilot <[email protected]>
Co-authored-by: Tim Möhlmann <[email protected]>
# Eventstore fixes
- `event.Position` used float64 before which can lead to [precision
loss](https://github.com/golang/go/issues/47300). The type got replaced
by [a type without precision
loss](https://github.com/jackc/pgx-shopspring-decimal)
- the handler reported the wrong error if the current state was updated
and therefore took longer to retry failed events.
# Mirror fixes
- max age of auth requests can be configured to speed up copying data
from `auth.auth_requests` table. Auth requests last updated before the
set age will be ignored. Default is 1 month
- notification projections are skipped because notifications should be
sent by the source system. The projections are set to the latest
position
- ensure that mirror can be executed multiple times
---------
Co-authored-by: Livio Spring <[email protected]>
SilvanandGitHub
