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

06.03.2025 19:29, Nikhil Kumar Veldanda пишет:
> Hi,
>
>> Overall idea is great.
>>
>> I just want to mention LZ4 also have API to use dictionary. Its dictionary
>> will be as simple as "virtually prepended" text (in contrast to complex
>> ZStd dictionary format).
>>
>> I mean, it would be great if "dictionary" will be common property for
>> different algorithms.
>>
>> On the other hand, zstd have "super fast" mode which is actually a bit
>> faster than LZ4 and compresses a bit better. So may be support for
>> different algos is not essential. (But then we need a way to change
>> compression level to that "super fast" mode.)
>>
>
> zstd compression level and zstd dictionary size is configurable at
> attribute level using ALTER TABLE. Default zstd level is 3 and dict
> size is 4KB. For super fast mode level can be set to 1.

No. Super-fast mode levels are negative. See parsing "--fast" parameter in
`programs/zstdcli.c` in zstd's repository and definition of ZSTD_minCLevel().

So, to support "super-fast" mode you have to accept negative compression
levels. I didn't check, probably you're already support them?

-------
regards
Yura Sokolov aka funny-falcon