Re: Tow kinds of different result while using create index concurrently

Thanks Jeff

But What I can't understand is:
In My first test, the "create index concurrently" works well.
In My second test, the "create index concurrently" can not work.

The difference is only on ecpg's select statement :
One use host variable of char (its value is of integer 14) in select
statement,
While the other is just a simple select.

If the transaction will potentially the index, it should be same on my
first test and second test.

My customer want to use PG on their 7x24 environment, while rebuilding
index periodically.
If I can't do it on PG, it really confused me...

sincerely yours
Jian

2013/6/21 Jeff Janes <jeff(dot)janes(at)gmail(dot)com>

> On Thu, Jun 20, 2013 at 1:27 AM, 高健 <luckyjackgao(at)gmail(dot)com> wrote:
>
>> Hello:
>>
>>
>>
>> I have question about PG's "create index concurrently". I think it is a
>> bug perhaps.
>>
>>
>>
>> I make two tables tab01 and tab02, they have no relationships.
>>
>> I think "create index concurrently " on tab02 will not be influenced by
>> transaction on tab01.
>>
>> But the result differs:
>>
>
> This is expected. In order to not interfere with "normal" activity, a
> concurrent index build has to volunteer to be blocked by such activity
> instead. From the doc: "When this option is used, PostgreSQL must
> perform two scans of the table, and in addition it must wait for all
> existing transactions that could potentially use the index to terminate."
>
> Now in your case, perhaps the argument could be made that the transaction
> hosting the 1st concurrent build could not potentially use the 2nd-building
> index, but there is no convenient way for PostgreSQL to detect that fact.
>
> Cheers,
>
> Jeff
>