От: Chris Browne
Тема: Re: the XID question
Дата: ,
Msg-id: 878vyg9399.fsf@cbbrowne.afilias-int.info
(см: обсуждение, исходный текст)
Ответ на: the XID question  ("Charles.Hou")
Ответы: Re: the XID question  (Andres Freund)
Список: pgsql-performance

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the XID question  ("Charles.Hou", )
 Re: the XID question  ("Charles.Hou", )
 Re: the XID question  (Filip Rembiałkowski, )
  Re: the XID question  ("Kevin Grittner", )
 Re: the XID question  (Chris Browne, )
  Re: the XID question  (Andres Freund, )
   Re: the XID question  ("Kevin Grittner", )
    Re: the XID question  (Greg Smith, )
 Re: the XID question  ("Charles.Hou", )
  Re: the XID question  ("Kevin Grittner", )
   Re: the XID question  (Robert Haas, )
 Re: the XID question  ("Charles.Hou", )

 ("Kevin Grittner") writes:
> Filip Rembia*kowski<> wrote:
>> 2011/1/19 Charles.Hou <>:
>
>>> " select * from mybook" SQL command also increase the XID ?
>>
>> Yes. Single SELECT is a transaction. Hence, it needs a transaction
>> ID.
>
> No, not in recent versions of PostgreSQL.  There's virtual
> transaction ID, too; which is all that's needed unless the
> transaction writes something.
>
> Also, as a fine point, if you use explicit database transactions
> (with BEGIN or START TRANSACTION) then you normally get one XID for
> the entire transaction, unless you use SAVEPOINTs.

Erm, "not *necessarily* in recent versions of PostgreSQL."

A read-only transaction won't consume XIDs, but if you don't expressly
declare it read-only, they're still liable to get eaten...
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