Re: jsonb format is pessimal for toast compression

On Mon, Sep 15, 2014 at 4:09 PM, Josh Berkus <josh(at)agliodbs(dot)com> wrote:
> On 09/15/2014 10:23 AM, Claudio Freire wrote:
>> Now, large small keys could be 200 or 2000, or even 20k. I'd guess
>> several should be tested to find the shape of the curve.
>
> Well, we know that it's not noticeable with 200, and that it is
> noticeable with 100K. It's only worth testing further if we think that
> having more than 200 top-level keys in one JSONB value is going to be a
> use case for more than 0.1% of our users. I personally do not.

Yes, but bear in mind that the worst case is exactly at the use case
jsonb was designed to speed up: element access within relatively big
json documents.

Having them uncompressed is expectable because people using jsonb will
often favor speed over compactness if it's a tradeoff (otherwise
they'd use plain json).

So while you're right that it's perhaps above what would be a common
use case, the range "somewhere between 200 and 100K" for the tipping
point seems overly imprecise to me.