From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
---|---|
To: | Nicolas Barbier <nicolas(dot)barbier(at)gmail(dot)com> |
Cc: | Peter Geoghegan <pg(at)heroku(dot)com>, Leonardo Francalanci <m_lists(at)yahoo(dot)it>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Fast insertion indexes: why no developments |
Date: | 2013-11-12 22:14:00 |
Message-ID: | CA+U5nMK5F-M_nwLLXQ-DhVLGR=6+hVDwBNfH3429tbKQ1jL8Yw@mail.gmail.com |
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Lists: | pgsql-hackers |
On 12 November 2013 21:41, Nicolas Barbier <nicolas(dot)barbier(at)gmail(dot)com> wrote:
> Look-up speed is as follows: Each look-up must look through all
> B-trees.
That can be optimised by using a min max approach, so we need only
look at sub-trees that may contain data.
> Index size: I think (didn’t calculate) that the combined size of the
> B-trees will be about the same as (a little bit more than) the size of
> a single big B-tree containing the same entries.
Agreed
> Major missing piece in PostgreSQL (I think):
>
> * Functionality to merge K indexes into one (bigger) combined index.
Good analysis.
I would add that it is possible to optimise large DELETEs from a table
if complete sub-trees of the btree can be easily removed. This for me
would be the compelling benefit of this approach.
I still think we need to look at this from a query perspective though.
We need to check whether there is a class of real world queries that
are not well optimised by minmax indexes, or cannot be made to be in
future releases. For example, large DELETEs from a table are almost
trivially optimised for min max.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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