Re: ZStandard (with dictionaries) compression support for TOAST compression

Hi Robert,

> I think that solving the problems around using a dictionary is going
> to be really hard. Can we see some evidence that the results will be
> worth it?

With the latest patch I've shared,

Using a Kaggle dataset of Nintendo-related tweets[1], we leveraged
PostgreSQL's acquire_sample_rows function to quickly gather just 1,000
sample rows for a specific attribute out of 104695 rows. These raw
samples were passed into Zstd's sampling buffer, generating a custom
dictionary. This dictionary was then directly used to compress the
documents, resulting in 62% of space savings after compressed:

```
test=# \dt+
List of tables
Schema | Name | Type | Owner | Persistence | Access
method | Size | Description
--------+----------------+-------+----------+-------------+---------------+--------+-------------
public | lz4 | table | nikhilkv | permanent | heap
| 297 MB |
public | pglz | table | nikhilkv | permanent | heap
| 259 MB |
public | zstd_with_dict | table | nikhilkv | permanent | heap
| 114 MB |
public | zstd_wo_dict | table | nikhilkv | permanent | heap
| 210 MB |
(4 rows)
```

We've observed similarly strong results on other datasets as well with
using dictionaries.

[1] https://www.kaggle.com/code/dcalambas/nintendo-tweets-analysis/data

---
Nikhil Veldanda