| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Andrew Dunstan <andrew(at)dunslane(dot)net> |
| Cc: | Bruce Momjian <bruce(at)momjian(dot)us>, Peter Geoghegan <pg(at)heroku(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Robert Haas <robertmhaas(at)gmail(dot)com>, Kevin Grittner <kgrittn(at)ymail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>, Larry White <ljw1001(at)gmail(dot)com> |
| Subject: | Re: jsonb format is pessimal for toast compression |
| Date: | 2014-08-14 02:36:45 |
| Message-ID: | 22146.1407983805@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
> On 08/13/2014 09:01 PM, Tom Lane 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 ;-).
> What does changing to lengths do to the speed of other operations?
This was explicitly *not* an attempt to measure the speed issue. To do
a fair trial of that, you'd have to work a good bit harder, methinks.
Examining each of N items would involve O(N^2) work with the patch as
posted, but presumably you could get it down to less in most or all
cases --- in particular, sequential traversal could be done with little
added cost. But it'd take a lot more hacking.
regards, tom lane
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