Re: Index Skip Scan

On 3/1/19 12:03 AM, Thomas Munro wrote:
> On Fri, Mar 1, 2019 at 11:23 AM Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:
>> On Thu, Jan 31, 2019 at 1:32 AM Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>>> At Wed, 30 Jan 2019 18:19:05 +0100, Dmitry Dolgov <9erthalion6(at)gmail(dot)com> wrote in <CA+q6zcVP18wYiO=aa+fz3GuncuTF52q1sufB7ise37TJPSDK1w(at)mail(dot)gmail(dot)com>
>>>> A bit of adjustment after nodes/relation -> nodes/pathnodes.
>>>
>>> I had a look on this.
>>>
>>> The name "index skip scan" is a different feature from the
>>> feature with the name on other prodcuts, which means "index scan
>>> with postfix key (of mainly of multi column key) that scans
>>> ignoring the prefixing part" As Thomas suggested I'd suggest that
>>> we call it "index hop scan". (I can accept Hopscotch, either:p)
>>
>>
>> I think that what we have proposed here is just an incomplete implementation of what other products call a skip scan, not a fundamentally different thing. They don't ignore the prefix part, they use that part in a way to cancel itself out to give the same answer, but faster. I think they would also use this skip method to get distinct values if that is what is requested. But they would go beyond that to also use it to do something similar to the plan we get with this:
>
> Hi Jeff,
>
> "Hop scan" was just a stupid joke that occurred to me when I saw that
> DB2 had gone for "jump scan". I think "skip scan" is a perfectly good
> name and it's pretty widely used by now (for example, by our friends
> over at SQLite to blow us away at these kinds of queries).
>

+1 to "hop scan"

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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