| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi> |
| Cc: | Pierre C <lists(at)peufeu(dot)com>, francois(dot)perou(at)free(dot)fr, Josh Berkus <josh(at)agliodbs(dot)com>, Craig Ringer <craig(at)postnewspapers(dot)com(dot)au>, Andrew Dunstan <andrew(at)dunslane(dot)net>, pgsql-hackers(at)postgresql(dot)org, dpage(at)pgadmin(dot)org |
| Subject: | Re: SQL compatibility reminder: MySQL vs PostgreSQL |
| Date: | 2010-03-08 14:44:51 |
| Message-ID: | 603c8f071003080644t2400ef0r4263b0ac12e3cec6@mail.gmail.com |
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On Mon, Mar 8, 2010 at 4:58 AM, Marko Tiikkaja
<marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi> wrote:
> On 2010-03-08 11:47 +0200, Pierre C wrote:
>>> As far as I can tell, we already do index skip scans:
>>
>> This feature is great but I was thinking about something else, like SELECT
>> DISTINCT, which currently does a seq scan, even if x is indexed.
>>
>> Here is an example. In both cases it could use the index to skip all
>> non-interesting rows, pulling only 69 rows from the heap instead of 120K.
>
> Oh, this is what I believe MySQL calls "loose index scans". I'm
> actually looking into this as we speak, but there seems to be a
> non-trivial amount of work to be done in order for this to work.
We should probably have a TODO for this, if we don't already.
...Robert
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