| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com> |
| Cc: | Andrey Borodin <x4mmm(at)yandex-team(dot)ru>, Robert Haas <robertmhaas(at)gmail(dot)com>, Daniil Zakhlystov <usernamedt(at)yandex-team(dot)ru>, Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru>, Denis Smirnov <sd(at)arenadata(dot)io>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: libpq compression |
| Date: | 2020-12-22 19:33:22 |
| Message-ID: | 630701.1608665602@sss.pgh.pa.us |
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Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com> writes:
> On 12/22/20 8:03 PM, Tom Lane wrote:
>> The link Ken pointed at suggests that restricting the window size to
>> 8MB is a common compromise. It's not clear to me what that does to
>> the achievable compression ratio. Even 8MB could be an annoying cost
>> if it's being paid per-process, on both the server and client sides.
> Possibly, but my understanding is that's merely a recommendation for the
> decoder library (e.g. libzstd), and it's not clear to me if/how that
> relates to the compression level or how to influence it.
> From the results shared by Daniil, the per-client overhead seems way
> higher than 8MB, so either libzstd does not respect this recommendation
> or maybe there's something else going on.
I'd assume that there's a direct correlation between the compression level
setting and the window size; but I've not studied the libzstd docs in
enough detail to know what it is.
regards, tom lane
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