Re: jsonb format is pessimal for toast compression

Josh Berkus <josh(at)agliodbs(dot)com> writes:
> On 09/25/2014 10:26 AM, Andres Freund wrote:
>> On 2014-09-25 10:25:24 -0700, Josh Berkus wrote:
>>> If Heikki says it's ready, I'll test. So far he's said that it wasn't
>>> done yet.

>> http://www.postgresql.org/message-id/541C242E.3030004@vmware.com

> Yeah, and that didn't include some of Tom's bug fixes apparently, per
> the succeeding message. Which is why I asked Heikki if he was done, to
> which he has not replied.

I took a quick look at the two patches Heikki posted. I find the
"separate offsets array" approach unappealing. It takes more space
than the other approaches, and that space will be filled with data
that we already know will not be at all compressible. Moreover,
AFAICS we'd have to engrave the stride on stone tablets, which as
I already mentioned I'd really like to not do.

The "offsets-and-lengths" patch seems like the approach we ought to
compare to my patch, but it looks pretty unfinished to me: AFAICS it
includes logic to understand offsets sprinkled into a mostly-lengths
array, but no logic that would actually *store* any such offsets,
which means it's going to act just like my patch for performance
purposes.

In the interests of pushing this forward, I will work today on
trying to finish and review Heikki's offsets-and-lengths patch
so that we have something we can do performance testing on.
I doubt that the performance testing will tell us anything we
don't expect, but we should do it anyway.

regards, tom lane