| From: | Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> |
|---|---|
| To: | Mladen Gogala <mladen(dot)gogala(at)vmsinfo(dot)com> |
| Cc: | Igor Neyman <ineyman(at)perceptron(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, David Wilson <david(dot)t(dot)wilson(at)gmail(dot)com>, Kenneth Marshall <ktm(at)rice(dot)edu>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: Postgres 9.0 has a bias against indexes |
| Date: | 2011-01-27 20:59:15 |
| Message-ID: | AANLkTi=UR69=XG9=ttuVbyBJE847NiPYYzR2yp8S_Mok@mail.gmail.com |
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| Lists: | pgsql-performance |
On Thu, Jan 27, 2011 at 1:44 PM, Mladen Gogala
<mladen(dot)gogala(at)vmsinfo(dot)com> wrote:
> On 1/27/2011 3:37 PM, Scott Marlowe wrote:
>>
>> On Thu, Jan 27, 2011 at 1:31 PM, Mladen Gogala
>> <mladen(dot)gogala(at)vmsinfo(dot)com> wrote:
>>>
>>> There is INDEX UNIQUE SCAN PK_EMP. Oracle will use an index.
>>
>> That's because Oracle has covering indexes.
>>
> I am not sure what you mean by "covering indexes" but I hope that for the
> larger table I have in mind, indexes will be used. For a small table like
In Oracle you can hit JUST the index to get the data you need (and
maybe rollback logs, which are generally pretty small)
In Pgsql, once you hit the index you must then hit the actual data
store to get the right version of your tuple. So, index access in pg
is more expensive than in Oracle. However, updates are cheaper.
Always a trade off
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