Re: What is the difference between cmin and cmax - Mailing list pgsql-general

From Luca Ferrari
Subject Re: What is the difference between cmin and cmax
Date
Msg-id CAKoxK+6Z248ur31PFMv460OagMOaZBVLRkd7k4bDfmXuUdsE4Q@mail.gmail.com
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In response to Re: What is the difference between cmin and cmax  (高健 <luckyjackgao@gmail.com>)
List pgsql-general
On Tue, Jul 2, 2013 at 5:19 AM, 高健 <luckyjackgao@gmail.com> wrote:
> Hello:
> I looked into the source code, and I think I now understand it:
> cmin and cmax are same! The documentation is too old now.

Yes, you figured it out.
For short: cmin and cmax are overlapped fields and are used within the
same transaction to identify the command that changed a tuple, so that
in-transaction commands can be ordered and, therefore, tuple
visibility can be calculated.

Luca


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