Re: jsonb format is pessimal for toast compression

On 08/13/2014 09:01 PM, Tom Lane wrote:
> I wrote:
>> That's a fair question.  I did a very very simple hack to replace the item
>> offsets with item lengths -- turns out that that mostly requires removing
>> some code that changes lengths to offsets ;-).  I then loaded up Larry's
>> example of a noncompressible JSON value, and compared pg_column_size()
>> which is just about the right thing here since it reports datum size after
>> compression.  Remembering that the textual representation is 12353 bytes:
>> json:                382 bytes
>> jsonb, using offsets:        12593 bytes
>> jsonb, using lengths:        406 bytes
> Oh, one more result: if I leave the representation alone, but change
> the compression parameters to set first_success_by to INT_MAX, this
> value takes up 1397 bytes.  So that's better, but still more than a
> 3X penalty compared to using lengths.  (Admittedly, this test value
> probably is an outlier compared to normal practice, since it's a hundred
> or so repetitions of the same two strings.)
>
>             



What does changing to lengths do to the speed of other operations?

cheers

andrew