# Elastic Cloud: Major incident: Replication bug causing slow recoveries

**Summary:** Elastic Cloud Hosted reported major degradation from 2026-09-01 08:16 UTC to 2026-09-30 20:44 UTC (29 days 12 h). In Elasticsearch 9.5.0, 9.5.1 and 9.5.2, bulk indexing could cause replica divergence, high disk usage and long-running recoveries. Elastic fixed the bug in 9.5.3 and advised affected customers to upgrade and follow workaround steps. _(machine-written, sol)_
- Kind: Major incident · Label: degradation (model (Jev))
- Changed: 2026-09-01 08:16 UTC · Detected: 2026-10-17 18:22 UTC
- [Source: https://stspg.io/nx73hprsrgph](https://stspg.io/nx73hprsrgph)
- [Company: Elastic Cloud](https://rewindex.com/company/elastic-cloud.md)
- Versions: before (none: first archived) → after incident\_version:276/l6zgdnvvg41j@8b8fa21479c1
- Change 1 of 1 for this incident

## What changed

**1. Added: Title**

```diff
+ Replication bug causing slow recoveries
```

**2. Added: Impact**

```diff
+ major
```

**3. Added: Status**

```diff
+ resolved
```

**4. Added: Start time**

```diff
+ 2026-09-01 08:16 UTC
```

**5. Added: Resolved time**

```diff
+ 2026-09-30 20:44 UTC
```

**6. Added: Affected components**

```diff
+ Elastic Cloud Hosted
```

**7. Added: Update** (investigating) · 2026-09-01 08:16 UTC

```diff
+ We are aware of a bug affecting customers on Elasticsearch versions 9.5.0, 9.5.1 and 9.5.2 where bulk index operations processed on the primary shard can result in divergence on the replicas resulting in high disk usage and long-running recoveries. The team is working on a fix. More information can be found on https://www.elastic.co/docs/release-notes/elasticsearch/known-issues#elasticsearch-9.5.2-known-issues The next update will be in the next 2 hours or sooner if needed.
```

**8. Added: Update** (identified) · 2026-09-01 11:07 UTC

```diff
+ We have identified the root cause and the team is working on a fix scheduled to be released in Elasticsearch version 9.5.3 What you can do: - If you have not yet upgraded to 9.5.*, you are not affected as upgrades to 9.5 have been disabled until 9.5.3 is released - If you are already running 9.5 and experience the symptoms of this issue, please contact Elastic Support. More information can be found on https://www.elastic.co/docs/release-notes/elasticsearch/known-issues#elasticsearch-9.5.2-known-issues
```

**9. Added: Update** (identified) · 2026-09-01 15:46 UTC

```diff
+ The fix has been identified and backported to the Elasticsearch 9.5 patch branch. The teams are performing the needed validations before scheduling and rolling out the 9.5.3 release.
```

**10. Added: Update** (monitoring) · 2026-09-03 12:13 UTC

```diff
+ Elasticsearch 9.5.3 has been released and all customers currently running 9.5.0, 9.5.1 or 9.5.2 are advised to update to this new version as soon as possible.
```

**11. Added: Update** (monitoring) · 2026-09-03 15:47 UTC

```diff
+ Elasticsearch 9.5.3 has been released and all customers currently running 9.5.0, 9.5.1 or 9.5.2 are advised to update to this new version as soon as possible. Impacted customers are advised to follow the workaround steps from https://github.com/elastic/elasticsearch/issues/158212 after the upgrade.
```

**12. Added: Update** (resolved) · 2026-09-30 20:44 UTC

```diff
+ This issue was resolved in the 9.5.3 release of Elasticsearch.  Customers running versions 9.5.0, 9.5.1, or 9.5.2 of Elasticsearch are advised to update to a newer version as soon as possible.
```

## History of this incident

| When (UTC) | Change | Label |
| --- | --- | --- |
| 2026-09-01 08:16 UTC | Major incident: Replication bug causing slow recoveries (this change) | degradation |

All Elastic Cloud changes: [timeline](https://rewindex.com/company/elastic-cloud/changes.md)
_Diff excerpts are shown on normalized text: dates, counters and tokens appear as ‹date›, ‹count›, ‹tok›; noise-only edits are hidden. Rewindex shows the changed passages, not a copy of the page._


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Canonical: https://rewindex.com/change/iedeb5464aab1e4 · Markdown: https://rewindex.com/change/iedeb5464aab1e4.md · JSON: https://rewindex.com/api/v1/changes/iedeb5464aab1e4 · Generated 2026-10-18T02:54:56.276Z