Re: jsonb format is pessimal for toast compression

Stephen Frost <sfrost@snowman.net> writes:
> * Tom Lane (tgl@sss.pgh.pa.us) wrote:

> I'm rather disinclined to change the on-disk format because of this
> specific test, that feels a bit like the tail wagging the dog to me,
> especially as I do hope that some day we'll figure out a way to use a
> better compression algorithm than pglz.

I'm unimpressed by that argument too, for a number of reasons:

1. The real problem here is that jsonb is emitting quite a bit of
fundamentally-nonrepetitive data, even when the user-visible input is very
repetitive.  That's a compression-unfriendly transformation by anyone's
measure.  Assuming that some future replacement for pg_lzcompress() will
nonetheless be able to compress the data strikes me as mostly wishful
thinking.  Besides, we'd more than likely have a similar early-exit rule
in any substitute implementation, so that we'd still be at risk even if
it usually worked.