| From: | Paul Ramsey <pramsey(at)cleverelephant(dot)ca> |
|---|---|
| To: | Andrey Borodin <x4mmm(at)yandex-team(dot)ru> |
| Cc: | Владимир Лесков <vladimirlesk(at)yandex-team(dot)ru>, Stephen Frost <sfrost(at)snowman(dot)net>, Daniel Verite <daniel(at)manitou-mail(dot)org>, Simon Riggs <simon(at)2ndquadrant(dot)com>, rafia(dot)sabih(at)enterprisedb(dot)com, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Compressed TOAST Slicing |
| Date: | 2019-04-09 17:12:56 |
| Message-ID: | 9136FFD1-EE77-4D90-9856-AFFDF117BCB8@cleverelephant.ca |
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| Lists: | pgsql-hackers |
> On Apr 9, 2019, at 10:09 AM, Andrey Borodin <x4mmm(at)yandex-team(dot)ru> wrote:
>
> He advised me to use algorithm that splits copied regions into smaller non-overlapping subregions with exponentially increasing size.
>
> while (off <= len)
> {
> memcpy(dp, dp - off, off);
> len -= off;
> dp += off;
> off *= 2;
> }
> memcpy(dp, dp - off, len);
>
> On original Paul's test without patch of this thread this optimization gave about x2.5 speedup.
> I've composed more detailed tests[0] and tested against current master. Now it only gives 20%-25% of decompression speedup, but I think it is still useful.
Wow, well beyond slicing, just being able to decompress 25% faster is a win for pretty much any TOAST use case. I guess the $100 question is: portability? The whole reason for the old-skool code that’s there now was concerns about memcpy’ing overlapping addresses and Bad Things happening.
P.
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