# Big drop in indexing rate when reindexing

**URL:** <https://discuss.elastic.co/t/big-drop-in-indexing-rate-when-reindexing/377310>\
**Category:** Elasticsearch\
**Created:** [April 19, 2025, 8:18am UTC](https://discuss.elastic.co/t/big-drop-in-indexing-rate-when-reindexing/377310 "2025-04-19T08:18:04Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![parameter](https://avatars.discourse-cdn.com/v4/letter/p/7c8e57/32.png) [@parameter](https://discuss.elastic.co/u/parameter)\
**Post date:** [April 19, 2025, 8:18am UTC](https://discuss.elastic.co/t/big-drop-in-indexing-rate-when-reindexing/377310/1 "2025-04-19T08:18:04Z")

</div>

I'm reindexing timeseries data into bigger indices. I have daily indices like `logs-yyyy-MM-dd` and I'm reindexing it to bigger indices using:

```json
POST _reindex
{
  "source": {
    "index": "logs-2024-08-*"
  },
  "dest": {
    "index": "logs-2024-08"
  }
}

```

I've done this by one month at a time and it has taken some time it has generally worked fine. The document count for each month has been 50-60 M.

For more recent indices the document count is higher - 80-120 M. The index rate seems to have dropped abruptly around 45-50 M documents, and steadily decreasing after...

 ![Pasted image 20250419095030](https://us1.discourse-cdn.com/elastic/original/3X/a/8/a83ad62d3d774c60b3ea807d0a57813551a8e88d.png)

When starting new reindex jobs now, the index rate never approaches the rates I had earlier.

It's a cluster with 3 EC2 nodes - using EBS gp3 volumes. I can see that Volume IOPS exceeded check has been 1 since about the same time as the abrupt drop in index rate, but since gp3 are not burstable I don't think this is the issue? (I'm not allowed to include more screenshot since I'm a new user).

---

<div class="post-metadata">

**Author:** ![parameter](https://avatars.discourse-cdn.com/v4/letter/p/7c8e57/32.png) [@parameter](https://discuss.elastic.co/u/parameter)\
**Post date:** [April 19, 2025, 9:40am UTC](https://discuss.elastic.co/t/big-drop-in-indexing-rate-when-reindexing/377310/2 "2025-04-19T09:40:18Z")

</div>

I had ~10 re-indexing jobs running so I canceled 3 (those with most documents remaining). After this Volume IOPS exceeded metric changed from 1 to 0 (only one of the 3 had exceeded this) and the indexing rate boosted up to 2000-3000/s. So, problem solved - and volume IOPS exceeeded is crucial to watch out for!