Address WAL alerts on the sec DB
## Objective
Address recurring WAL-generation alerts on the GitLab.com `sec` PostgreSQL database (`patroni-sec`) by reducing concurrent write pressure from security/SBOM ingestion workers and correcting the alerting logic.
## Context
The `PrimaryDatabaseWALGenerationSaturationSpike` alert fired for `patroni-sec` in `gprd` below the 70% soft SLO. The initial investigation identified high write activity from `Sbom::IngestReportsWorker` and `Security::StoreSecurityReportsByProjectWorker` as the primary driver, alongside PostgreSQL autovacuum activity on the same tables.
The alert fired again on 2026-09-14, with `patroni-sec` WAL saturation peaking at 62.6%, still below the 70% soft SLO, and the alert's z-score reading between 5.4 and 6.2 against its 3.5 threshold. Per the [linked dashboard](https://dashboards.gitlab.net/explore?schemaVersion=1&panes=%7B%22vac%22:%7B%22datasource%22:%22mimir-gitlab-gprd%22,%22queries%22:%5B%7B%22refId%22:%22A%22,%22expr%22:%22pg_stat_user_tables_n_dead_tup%7Btype%3D%5C%22patroni-sec%5C%22,%20env%3D%5C%22gprd%5C%22,%20relname%3D~%5C%22sbom_graph_paths%7Cvulnerability_occurrences%7Cvulnerability_occurrence_identifiers%7Cvulnerabilities%7Cvulnerability_reads%7Cvulnerability_identifiers%7Csecurity_finding_enrichments%7Csbom_occurrences%7Csecurity_scans%5C%22%7D%22,%22legendFormat%22:%22%7B%7Brelname%7D%7D%22,%22datasource%22:%7B%22type%22:%22prometheus%22,%22uid%22:%22mimir-gitlab-gprd%22%7D,%22editorMode%22:%22code%22,%22range%22:true,%22instant%22:true%7D%5D,%22range%22:%7B%22from%22:%221789395356858%22,%22to%22:%221789404694727%22%7D,%22compact%22:false%7D%7D&orgId=1), there was no notable rise in dead tuples on the sec tables under watch (`sbom_graph_paths`, `vulnerability_occurrences`, `vulnerability_occurrence_identifiers`, `vulnerabilities`, `vulnerability_reads`, `vulnerability_identifiers`, `security_finding_enrichments`, `sbom_occurrences`, `security_scans`) during that window, and the WAL rise was sharp rather than gradual.
This means autovacuum activity is not a necessary precondition for these WAL spikes: sharp write bursts alone produce them. Autovacuum may still amplify WAL when it happens to be running in parallel, but the epic no longer treats it as the mechanism.
This splits the work into two independent problems: reducing write volume from the ingestion workers, and correcting the alert. Neither fixes the other — the worker deferrals will not stop a below-SLO false positive, and fixing the alert will not reduce write volume. The database-health deferral fixes are now merged and their feature flags have been enabled; the remaining alerting work is to implement and validate the revised WAL alert query and thresholds.
## Scope / child issues
- [AutovacuumActiveOnTable always queries main, ignoring context.connection](https://gitlab.com/gitlab-org/gitlab/-/work_items/628693) — related MRs [!254976](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/254976), [!254955](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/254955), and [!255196](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/255196).
- [[Feature flag] Rollout of `defer_sbom_ingest_reports_on_database_health`](https://gitlab.com/gitlab-org/gitlab/-/work_items/628675) — [!254955](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/254955).
- [[Feature flag] Rollout of `defer_store_security_reports_on_database_health`](https://gitlab.com/gitlab-org/gitlab/-/work_items/628841) — [!255196](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/255196).
- [Implement revised sec DB WAL spike alert](https://gitlab.com/gitlab-org/gitlab/-/work_items/629102) — implement [runbooks!11560](https://gitlab.com/gitlab-com/runbooks/-/merge_requests/11560), including validation against live data and confirmation of the daily p99 tuning inputs.
## Evidence from the investigation
### Sec DB writes per job by worker class (2026-09-10)
Per-job sec-database write counts by Sidekiq worker class. `Sbom::IngestReportsWorker` peaked at 38,896 writes in a single job; the next-highest worker was 587.
[View screenshot and Kibana evidence in MR !254955](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/254955)
### Total sec DB write count for `Sbom::IngestReportsWorker` (2026-09-10)
Total sec-database writes for `Sbom::IngestReportsWorker`, 97,352 in one minute against a baseline of roughly 5,000 to 25,000.
[View screenshot and Kibana evidence in MR !254955](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/254955)
### WAL saturation and alert context (2026-09-10)
`patroni-sec` WAL saturation peaking at 65.9%, below the 70% soft SLO.
[View screenshot and Grafana evidence in MR !254955](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/254955)
[Grafana dashboard source](https://dashboards.gitlab.net/goto/cfxwmpoyla0w0f?orgId=1)
[Alert query / alert dashboard source](https://dashboards.gitlab.net/explore?schemaVersion=1&orgId=1&panes=%7B%2200v%22%3A%7B%22datasource%22%3A%22mimir-gitlab-gprd%22%2C%22queries%22%3A%5B%7B%22refId%22%3A%22A%22%2C%22expr%22%3A%22%28%28%28max_over_time%28rate%28pg_xlog_position_bytes%7Benv%3D%5C%22gprd%5C%22%2Ctype%3D%5C%22patroni-sec%5C%22%7D%5B5m%5D%29%5B1h%3A%5D%29+%3E%3D+%28100+%2A+1024+%2A+1024%29%29+-+avg_over_time%28rate%28pg_xlog_position_bytes%7Benv%3D%5C%22gprd%5C%22%2Ctype%3D%5C%22patroni-sec%5C%22%7D%5B5m%5D%29%5B1d%3A%5D%29%29+%2F+stddev_over_time%28rate%28pg_xlog_position_bytes%7Benv%3D%5C%22gprd%5C%22%2Ctype%3D%5C%22patroni-sec%5C%22%7D%5B5m%5D%29%5B1d%3A%5D%29+and+on+%28fqdn%29+%28pg_replication_is_replica+%3D%3D+0%29%29+%3E+3.5%22%2C%22range%22%3Atrue%2C%22instant%22%3Atrue%2C%22datasource%22%3A%7B%22type%22%3A%22prometheus%22%2C%22uid%22%3A%22mimir-gitlab-gprd%22%7D%2C%22editorMode%22%3A%22code%22%7D%5D%2C%22range%22%3A%7B%22from%22%3A%22now-1h%22%2C%22to%22%3A%22now%22%7D%7D%7D)
### `Security::StoreSecurityReportsByProjectWorker` evidence (2026-09-12)
Per-job writes showing `Security::StoreSecurityReportsByProjectWorker` at 2,807, second only to `Sbom::IngestReportsWorker` at 16,896. Note the panel is titled p99 but its legend series are prefixed (100), so these are peak per-job writes rather than a 99th percentile.
[Additional sec DB worker evidence in MR !255196](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/255196)
### 2026-09-14 event
The alert expression evaluated in Grafana, reading between 5.4 and 6.2 against its 3.5 threshold.
`patroni-sec` WAL saturation over four hours, peaking at 62.6% with a 4-hour mean of 24.9%, against the 70% soft SLO. Weekly p95 33.6%, weekly p99 44.4%.
- [Dead tuples on the watched sec tables during the window](https://dashboards.gitlab.net/explore?schemaVersion=1&panes=%7B%22vac%22:%7B%22datasource%22:%22mimir-gitlab-gprd%22,%22queries%22:%5B%7B%22refId%22:%22A%22,%22expr%22:%22pg_stat_user_tables_n_dead_tup%7Btype%3D%5C%22patroni-sec%5C%22,%20env%3D%5C%22gprd%5C%22,%20relname%3D~%5C%22sbom_graph_paths%7Cvulnerability_occurrences%7Cvulnerability_occurrence_identifiers%7Cvulnerabilities%7Cvulnerability_reads%7Cvulnerability_identifiers%7Csecurity_finding_enrichments%7Csbom_occurrences%7Csecurity_scans%5C%22%7D%22,%22legendFormat%22:%22%7B%7Brelname%7D%7D%22,%22datasource%22:%7B%22type%22:%22prometheus%22,%22uid%22:%22mimir-gitlab-gprd%22%7D,%22editorMode%22:%22code%22,%22range%22:true,%22instant%22:true%7D%5D,%22range%22:%7B%22from%22:%221789395356858%22,%22to%22:%221789404694727%22%7D,%22compact%22:false%7D%7D&orgId=1)
### Kibana saved views: sec DB writes by worker
Current saved views for per-worker sec-database writes:
- [Per-job write p99 by Sidekiq worker class](https://log.gprd.gitlab.net/app/r/s/yFacm)
- [Writes by worker class, including the all-workers total](https://log.gprd.gitlab.net/app/r/s/nsCBr)
Original 2026-09-10 views:
- [Kibana source (per-job writes)](https://log.gprd.gitlab.net/app/r/s/fKE7c)
- [Kibana source (total writes)](https://log.gprd.gitlab.net/app/r/s/zeaJX)
### Persistent noisy worker, 2026-09-15
{{width=900}}
`Sec DB writes per job - p99 by worker class (gprd)`, aggregating the 99th percentile of
`json.db_sec_write_count`, over 01:58 to 05:11 on 2026-09-15. This panel is genuinely a p99:
its legend series are prefixed `(99)`, unlike the 2026-09-12 panel whose series were `(100)`.
`Sbom::IngestReportsWorker` reaches a p99 of 15,797 writes in a single job, roughly 42 times
the next-highest worker:
| Worker | p99 writes per job |
|---|---|
| `Sbom::IngestReportsWorker` | 15,797 |
| `Security::StoreSecurityReportsByProjectWorker` | 372 |
| `Security::StoreScansWorker` | 74.4 |
| `Sbom::BuildDependencyGraphWorker` | 26.1 |
| `Sbom::RemoveOldDependencyGraphsWorker` | 25.4 |
The shape matters as much as the peak: it spikes to between 8,000 and 10,000 writes per job
every few minutes across the whole three-hour window, so this is sustained behaviour rather
than a single burst.
- [Kibana source](https://log.gprd.gitlab.net/app/r/s/Z5uLS)
## Related sources
- [Slack investigation thread](https://gitlab.slack.com/archives/C07TM9WFQJY/p1789080198423539)
- [WAL saturation runbook](https://runbooks.gitlab.com/patroni/primary_db_node_wal_generation_saturation/)
- [Runbook MR !11560](https://gitlab.com/gitlab-com/runbooks/-/merge_requests/11560)
## Definition of done
- The worker deferral and autovacuum connection fixes are rolled out and monitored.
- The revised WAL alert query is implemented, validated against live data, and tuned so soft-SLO breaches alert without reproducing the below-SLO false positives.
- The alert does not fire below the soft SLO, and reaching the soft SLO does alert — the saturation framework currently alerts only at the hard SLO, so there is no soft-SLO coverage today. See [runbooks!11560](https://gitlab.com/gitlab-com/runbooks/-/merge_requests/11560).
- The updated alert behaviour and operational dashboards/runbook are documented.
epic
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