Untested pseudo-code:
```rb
def last_posted_topic
[sitemap_topics.maximum(:bumped_at), sitemap_topics.maximum(:updated_at)].max
end
```
---
### Author:  [@sam](https://meta.discourse.org/u/sam)
#### Post date: [March 18, 2024, 12:25am UTC](https://meta.discourse.org/t/sitemap-lastmod-for-sitemaps-wrong/299702/2 "2024-03-18T00:25:05Z")
I am worried that an optimisation here complicates stuff enormously for very little benefit.
Think it through …
Say there are 6 chunks on meta. If a topic from the last chunk is touched… the entire chunk becomes invalid, you got to remove the topic from there and put it in the front chunk.
Optimising here is a little pointless for a site that sees any kind of activity and the dates inside the chunk on the actual topics are fine.
---
### Author:  [@rrit](https://meta.discourse.org/u/rrit)
#### Post date: [March 19, 2024, 1:33pm UTC](https://meta.discourse.org/t/sitemap-lastmod-for-sitemaps-wrong/299702/3 "2024-03-19T13:33:07Z")
It’s not about moving topics into different sitemap-chunks. The topics can stay in the same sitemap-chunk where they are already in.
(The mapping topic-to-sitemap-chunk is arbitrary anyway as the db `select`-statement with `limit` has no `order` defined.)
The bug report is about that the lastmod date of each sitemap-chunk should represent the lastmod date of the latest topic which the sitemap-chunk contains.
The way for Google should be:
1. Load `sitemap.xml`
→ Check `lastmod` of sitemap-chunks and queue sitemap-chunks which need an update
(lastmod date is newer than last time downloaded)
2. Load queued sitemap-chunks `sitemap_[1-5].xml`
→ Check `lastmod` of topic-urls and queue topic-urls which need an update
(lastmod date is newer than last time downloaded)
3. Load queued topic-urls.
If in `sitemap.xml` the lastmod of the sitemap-chunks is wrong:
→ Google does not queue changed sitemaps-chunks (step 1)
→ Google does not update changed sitemap-chunks in a timely manner (step 2)
→ Google does not update changed topics in a timely manner (step 3)
Right now [https://meta.discourse.org/sitemap.xml](https://meta.discourse.org/sitemap.xml) looks like this:
- [https://meta.discourse.org/sitemap\_1.xml](https://meta.discourse.org/sitemap_1.xml)
lastmod: 2024-03-19T **12** :50:09Z
All topics inside have older or same date? :github_check:
- [https://meta.discourse.org/sitemap\_2.xml](https://meta.discourse.org/sitemap_2.xml)
lastmod: 2024-03- **16** T12:59:17Z
All topics inside have older or same date? ❌
- [https://meta.discourse.org/sitemap\_3.xml](https://meta.discourse.org/sitemap_3.xml)
lastmod: 2024-03- **16** T12:59:17Z
All topics inside have older or same date? ❌
- [https://meta.discourse.org/sitemap\_4.xml](https://meta.discourse.org/sitemap_4.xml)
lastmod: 2024-03- **16** T12:59:17Z
All topics inside have older or same date? ❌
- [https://meta.discourse.org/sitemap\_5.xml](https://meta.discourse.org/sitemap_5.xml)
lastmod: 2024-03- **16** T12:59:17Z
All topics inside have older or same date? ❌
- [https://meta.discourse.org/sitemap\_recent.xml](https://meta.discourse.org/sitemap_recent.xml)
2024-03-19T13: **03** :41Z
All topics inside have older or same date? :github_check:
---
### Author:  [@sam](https://meta.discourse.org/u/sam)
#### Post date: [March 20, 2024, 1:18am UTC](https://meta.discourse.org/t/sitemap-lastmod-for-sitemaps-wrong/299702/4 "2024-03-20T01:18:38Z")
Again this is not strictly true … last\_mod is meant to be the last date the sitemap was modified not max date of topics.
If a topic dropped out of the sitemap section today and last modified in the chunk is a week a go… the chunk changed today. A topic dropped out of it today.
---
### Author:  [@rrit](https://meta.discourse.org/u/rrit)
#### Post date: [March 20, 2024, 12:59pm UTC](https://meta.discourse.org/t/sitemap-lastmod-for-sitemaps-wrong/299702/5 "2024-03-20T12:59:13Z")
> [@sam](#):
>
> If a topic dropped out of the sitemap section today and last modified in the chunk is a week a go… the chunk changed today _[note: not 3 days ago]_. A topic dropped out of it today.
This is totally true.
So the very same logic results in:
If a topic in the sitemap section changed today and last modified in the chunk is today… the chunk changed today _[note: not 3 days ago]_. A topic in it changed today.
For your and my example above the implementation right now says:
sitemap-chunks `sitemap_[2-5].xml` changed 3 days ago. This is wrong. It should say ‘changed today’.
---
### Author:  [@rrit](https://meta.discourse.org/u/rrit)
#### Post date: [March 20, 2024, 2:12pm UTC](https://meta.discourse.org/t/sitemap-lastmod-for-sitemaps-wrong/299702/6 "2024-03-20T14:12:52Z")
Here is the bigger picture behind all this:
`sitemap_recent.xml`:
- Only includes all the changed topics from the last 3 days
- Is renewed every 1 h (Internal Rails cache time of 1 h)
- Has correct lastmod date in `sitemap.xml`
`sitemap_[1-5].xml`:
- Really includes all and every topic, and also includes all the changed topics from the last 3 days
- Is renewed every 24 h (Internal Rails cache time of 24 h)
- `sitemap_[2-5].xml` have wrong lastmod date of `3.days.ago` in `sitemap.xml`
The wrong lastmod date for `sitemap_[2-5].xml` does not matter, as Google will get all recent topic changes via `sitemap_recent.xml` in a timely manner.