| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
| Cc: | Jan Wieck <jan(at)wi3ck(dot)info>, Craig Ringer <craig(at)2ndquadrant(dot)com>, Peter Geoghegan <pg(at)heroku(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, "Claudio Freire" <klaussfreire(at)gmail(dot)com>, "David E(dot) Wheeler" <david(at)justatheory(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Andrew Dunstan <andrew(at)dunslane(dot)net> |
| Subject: | Re: jsonb format is pessimal for toast compression |
| Date: | 2014-09-24 11:51:10 |
| Message-ID: | 13003.1411559470@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> writes:
> On 09/24/2014 08:16 AM, Tom Lane wrote:
>> Heikki's patch would eat up the high-order JEntry bits, but the other
>> points remain.
> If we don't need to be backwards-compatible with the 9.4beta on-disk
> format, we don't necessarily need to eat the high-order JEntry bit. You
> can just assume that that every nth element is stored as an offset, and
> the rest as lengths. Although it would be nice to have the flag for it
> explicitly.
If we go with this approach, I think that we *should* eat the high bit
for it. The main reason I want to do that is that it avoids having to
engrave the value of N on stone tablets. I think that we should use
a pretty large value of N --- maybe 32 or so --- and having the freedom
to change it later based on experience seems like a good thing.
regards, tom lane
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