Re: [JDBC] is a good practice to create an index on the oid?

От:

Dave Cramer <pg@fastcrypt.com>

Дата:

26 апреля 2004 г. в 20:00:08

Yes, you can create an index on the oid, but unless you are selecting on
it, it is of little use.

you would have to do select * from foo where oid=? to get any value out
of the index.

Dave
On Mon, 2004-04-26 at 12:38, Edoardo Ceccarelli wrote:
> I am using the oid of the table as the main key and I've found that is 
> not indexed (maybe because I have declared another primary key in the table)
> 
> it is a good practice to create an index like this on the oid of a table?
> CREATE INDEX idoid annuncio400 USING btree (oid);
> 
> 
> does it work as a normal index?
> 
> Thank you
> Edoardo
> 
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Dave Cramer
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Re: [JDBC] is a good practice to create an index on the

От:

Dave Cramer <pg@fastcrypt.com>

Дата:

27 апреля 2004 г. в 08:55:40

AFAIK, oids aren't used for anything internally, so duplicates don't
really matter. Besides, what would you do about duplicate oid's ?

The best suggestion is of course his last, don't use them.


On Mon, 2004-04-26 at 22:48, Christopher Kings-Lynne wrote:
> > I am using the oid of the table as the main key and I've found that is 
> > not indexed (maybe because I have declared another primary key in the 
> > table)
> > 
> > it is a good practice to create an index like this on the oid of a table?
> > CREATE INDEX idoid annuncio400 USING btree (oid);
> 
> Yes it is - in fact you really should add a unique index, not just a 
> normal index, as you want to enforce uniqueness of the oid column.  It 
> is theoretically possible to end up with duplicate oids in wraparound 
> situations.
> 
> Even better though is to not use oids at all, of course...
> 
> Chris
> 
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Dave Cramer
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Re: [JDBC] is a good practice to create an index on the

От:

Dave Cramer <pg@fastcrypt.com>

Дата:

27 апреля 2004 г. в 12:14:32

Edoardo, 

Are you using them for referential integrity? If so you would be wise to
use sequences instead. 

Christopher: yes you are correct, I wasn't sure if that is what he was
doing.

Dave
On Tue, 2004-04-27 at 11:01, Christopher Kings-Lynne wrote:
> > AFAIK, oids aren't used for anything internally, so duplicates don't
> > really matter. Besides, what would you do about duplicate oid's ?
> 
> If he's using them _externally_, then he does have to worry about 
> duplicates.
> 
> Chris
> 
> 
> 
> !DSPAM:408e75e0137721921318500!
> 
> 
-- 
Dave Cramer
519 939 0336
ICQ # 14675561

Re: [JDBC] is a good practice to create an index on the

От:

Bruno Wolff III <bruno@wolff.to>

Дата:

28 апреля 2004 г. в 05:39:44

On Wed, Apr 28, 2004 at 10:13:14 +0200,
  Edoardo Ceccarelli  wrote:
> do you mean that, declaring an index serial, I'd never have to deal with 
> incrementing its primary key? good to know!

That isn't what is happening. Serial is a special type. It is int plus
a default rule linked to a sequence. No index is created by default
for the serial type. Declaring a column as a primary key will however
create a unique index on that column.

Also note that you should only assume that the serial values are unique.
(This assumes that you don't use setval and that you don't roll a sequence
over.) Within a single session you can assume the sequence values will
be monotonicly increasing. The values that end up in your table can have
gaps. Typically this happens when a transaction rolls back after obtaining
a new value from a sequence. It can also happen if you grab sequence
values in larger blocks (which might be more efficient if a session normally
acquires mulitple values from a particular sequence) than the default 1.

> anyway  in this particular situation I don't need such accurate 
> behaviour: this table is filled up with a lot of data twice per week and 
> it's used only to answer queries.
> I could drop it whenever I want :)

You really don't want to use oids.

is a good practice to create an index on the oid?

От:

Edoardo Ceccarelli <eddy@axa.it>

Дата:

26 апреля 2004 г. в 17:57:46

I am using the oid of the table as the main key and I've found that is 
not indexed (maybe because I have declared another primary key in the table)

it is a good practice to create an index like this on the oid of a table?
CREATE INDEX idoid annuncio400 USING btree (oid);


does it work as a normal index?

Thank you
Edoardo

Re: is a good practice to create an index on the oid?

От:

Christopher Kings-Lynne <chriskl@familyhealth.com.au>

Дата:

26 апреля 2004 г. в 23:43:17

> I am using the oid of the table as the main key and I've found that is 
> not indexed (maybe because I have declared another primary key in the 
> table)
> 
> it is a good practice to create an index like this on the oid of a table?
> CREATE INDEX idoid annuncio400 USING btree (oid);

Yes it is - in fact you really should add a unique index, not just a 
normal index, as you want to enforce uniqueness of the oid column.  It 
is theoretically possible to end up with duplicate oids in wraparound 
situations.

Even better though is to not use oids at all, of course...

Chris

Re: [JDBC] is a good practice to create an index on the

От:

Christopher Kings-Lynne <chriskl@familyhealth.com.au>

Дата:

27 апреля 2004 г. в 12:01:34

> AFAIK, oids aren't used for anything internally, so duplicates don't
> really matter. Besides, what would you do about duplicate oid's ?

If he's using them _externally_, then he does have to worry about 
duplicates.

Chris

Re: [JDBC] is a good practice to create an index on the

От:

Edoardo Ceccarelli <eddy@axa.it>

Дата:

27 апреля 2004 г. в 18:43:45

I am going to use them as primary key of the table, so I'll surely need 
them unique :)
thank you for you help
Edoardo

Dave Cramer ha scritto:

>Edoardo, 
>
>Are you using them for referential integrity? If so you would be wise to
>use sequences instead. 
>
>Christopher: yes you are correct, I wasn't sure if that is what he was
>doing.
>
>Dave
>On Tue, 2004-04-27 at 11:01, Christopher Kings-Lynne wrote:
>  
>
>>>AFAIK, oids aren't used for anything internally, so duplicates don't
>>>really matter. Besides, what would you do about duplicate oid's ?
>>>      
>>>
>>If he's using them _externally_, then he does have to worry about 
>>duplicates.
>>
>>Chris
>>
>>
>>
>>!DSPAM:408e75e0137721921318500!
>>
>>
>>    
>>

Re: [JDBC] is a good practice to create an index on the

От:

Christopher Kings-Lynne <chriskl@familyhealth.com.au>

Дата:

27 апреля 2004 г. в 22:25:23

> I am going to use them as primary key of the table, so I'll surely need 
> them unique :)

Eduoardo, I REALLY suggest you don't use them at all.  You should make a 
primary key like this:

CREATE TABLE blah (
   id SERIAL PRIMARY KEY,
   ...
);

Also note that by default, OIDs are NOT dumped by pg_dump.  You will 
need to add extra switches to your pg_dump backup to ensure that they are.

Chris

Re: [JDBC] is a good practice to create an index on the

От:

Edoardo Ceccarelli <eddy@axa.it>

Дата:

28 апреля 2004 г. в 05:13:54

do you mean that, declaring an index serial, I'd never have to deal with 
incrementing its primary key? good to know!
anyway  in this particular situation I don't need such accurate 
behaviour: this table is filled up with a lot of data twice per week and 
it's used only to answer queries.
I could drop it whenever I want :)

Thanks again,
eddy

Christopher Kings-Lynne ha scritto:

>> I am going to use them as primary key of the table, so I'll surely 
>> need them unique :)
>
>
> Eduoardo, I REALLY suggest you don't use them at all.  You should make 
> a primary key like this:
>
> CREATE TABLE blah (
>   id SERIAL PRIMARY KEY,
>   ...
> );
>
> Also note that by default, OIDs are NOT dumped by pg_dump.  You will 
> need to add extra switches to your pg_dump backup to ensure that they 
> are.
>
> Chris
>
>
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Re: [JDBC] is a good practice to create an index on the

От:

Christopher Kings-Lynne <chriskl@familyhealth.com.au>

Дата:

28 апреля 2004 г. в 05:31:54

> do you mean that, declaring an index serial, I'd never have to deal with 
> incrementing its primary key? good to know!

Yep. You can use 'DEFAULT' as the value, eg:

INSERT INTO blah (DEFAULT, ...);

> anyway  in this particular situation I don't need such accurate 
> behaviour: this table is filled up with a lot of data twice per week and 
> it's used only to answer queries.
> I could drop it whenever I want :)

Sure.

Chris