From: Kevin Grittner <Kevin.Grittner@wicourts.gov>
To: Charles.Hou <givemeegn@gmail.com>
To: Filip Rembia*kowski <plk.zuber@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: the XID question
Date: Wed, 19 Jan 2011 08:39:47 -0600
Message-ID: <4D36A35302000025000397CC@gw.wicourts.gov> (raw)
In-Reply-To: <AANLkTim8MsWWPw3hL_U_U2cdv3us24MgP7TwcFJp2hVy@mail.gmail.com>
References: <ca4f167a-0c04-4c59-9dec-a10d8f43437b@i25g2000prd.googlegroups.com>
<AANLkTim8MsWWPw3hL_U_U2cdv3us24MgP7TwcFJp2hVy@mail.gmail.com>
Filip Rembia*kowski<plk.zuber@gmail.com> wrote:
> 2011/1/19 Charles.Hou <givemeegn@gmail.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.
-Kevin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: Kevin.Grittner@wicourts.gov, givemeegn@gmail.com, plk.zuber@gmail.com
Subject: Re: the XID question
In-Reply-To: <4D36A35302000025000397CC@gw.wicourts.gov>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox