Re: [GENERAL] Is the row version available in SQL? - Mailing list pgsql-general

From Chris Travers
Subject Re: [GENERAL] Is the row version available in SQL?
Date
Msg-id CAKt_Zfs6Lz02XO4=C9pw1wcM2AraFCiu2_ss53XEt9AnrQG0nA@mail.gmail.com
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In response to [GENERAL] Is the row version available in SQL?  (Rob Nikander <rob.nikander@gmail.com>)
Responses Re: [GENERAL] Is the row version available in SQL?
List pgsql-general


On Wed, Jun 28, 2017 at 4:54 PM, Rob Nikander <rob.nikander@gmail.com> wrote:
Hi,


In some cases I can use these transaction isolation modes, but in other cases, I may want to manage the versions and concurrency manually. Is there a way to select the “version” of a row, or is that data hidden to ordinary SQL statements?

I’m thinking about a sequence of actions, which are logically a transaction, but start on one thread and complete later on another thread. I don’t think I can tie up a JDBC database connection for that long. I can add a `version bigint` column to my table, and the final update will look like:

     update ... where id = ? and version = the_version_selected_earlier_in_a_different_thread

… and if that gets 0 rows, it can handle the conflict.
 
For that, you could use xmin.  That tracks the transaction where the row first became visible.

Best Wishes,
Chris Travers 

Rob





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Best Wishes,
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