Re: the XID question

Kevin(dot)Grittner(at)wicourts(dot)gov ("Kevin Grittner") writes:
> Filip Rembia*kowski<plk(dot)zuber(at)gmail(dot)com> wrote:
>> 2011/1/19 Charles.Hou <givemeegn(at)gmail(dot)com>:
>
>>> " 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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