Re: type cache cleanup improvements

Aleksander Alekseev <aleksander@timescale.com>

From: Aleksander Alekseev <aleksander@timescale.com>

To: Pgsql Hackers <pgsql-hackers@postgresql.org>

Cc: Teodor Sigaev <teodor@sigaev.ru>

Date: 2024-03-08T15:31:45Z

Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

Maintain RelIdToTypeIdCacheHash in TypeCacheOpcCallback()
- bb78e4267817 18.0 landed
Fix concurrrently in typcache_rel_type_cache.sql
- aa1e898dea66 18.0 landed
Avoid looping over all type cache entries in TypeCacheRelCallback()
- b85a9d046efd 18.0 landed
- c14d4acb8134 18.0 landed
Update header comment for lookup_type_cache()
- c1500a1ba7e1 18.0 landed
Revert: Avoid looping over all type cache entries in TypeCacheRelCallback()
- 8daa62a10c91 18.0 landed
Introduce hash_search_with_hash_value() function
- d0f020037e19 18.0 landed
Optimize InvalidateAttoptCacheCallback() and TypeCacheTypCallback()
- 40064a8ee1b3 18.0 landed
Refactor initial hash lookup in dynahash.c
- cc5ef90edd80 17.0 landed
Rationalize and improve error messages for some jsonpath items
- 92d2ab7554f9 17.0 cited
Avoid race in RelationBuildDesc() affecting CREATE INDEX CONCURRENTLY.
- fdd965d074d4 15.0 cited
Represent Lists as expansible arrays, not chains of cons-cells.
- 1cff1b95ab6d 13.0 cited

Attachments

v3-0001-Improve-performance-of-type-cache-cleanup.patch (application/octet-stream) patch v3-0001

Hi,

> > I would like to tweak the patch a little bit - change some comments,
> > add some Asserts, etc. Don't you mind?
> You are welcome!

Thanks. PFA the updated patch with some tweaks by me. I added the
commit message as well.

One thing that I couldn't immediately figure out is why 0 hash value
is treated as a magic invalid value in TypeCacheTypCallback():

```
-       hash_seq_init(&status, TypeCacheHash);
+       if (hashvalue == 0)
+               hash_seq_init(&status, TypeCacheHash);
+       else
+               hash_seq_init_with_hash_value(&status, TypeCacheHash,
hashvalue);
```

Is there anything that prevents the actual hash value from being zero?
I don't think so, but maybe I missed something.

If zero is indeed an invalid hash value I would like to reference the
corresponding code. If zero is a correct hash value we should either
change this by adding something like `if(!hash) hash++` or use an
additional boolean argument here.

-- 
Best regards,
Aleksander Alekseev